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Inspect the same-build implementation and its expressions or provider.", "/versions/10/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/10/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/10/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/10/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/10/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/10/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/10/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/10/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/10/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/10/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. 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"/versions/11/sections/3/title": "Same-version manual discussion", "/versions/11/sections/4/title": "Executor implementation notes", "/versions/11/sections/5/title": "EXPLAIN identity in core source", "/versions/11/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/11/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/11/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/11/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/11/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/11/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/11/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/11/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/11/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/11/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/11/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. 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["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/12/parallel-plans.html", "method": "same-major semantic node", "sha256": "4aaca92475f243dcddffd80d9af558330f8f3b0ac3cbe8872b0d2901e14fe684", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/12/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/12/facts/0/label": "Core node tag", "/versions/12/facts/1/label": "Structured EXPLAIN Node Type", "/versions/12/facts/2/label": "Inputs", "/versions/12/facts/2/value": "One ordered parallel child plan", "/versions/12/facts/3/label": "Output", "/versions/12/facts/3/value": "Merged ordered tuples", "/versions/12/facts/4/label": "Executor initializer", "/versions/12/facts/5/label": "Memory mechanism", "/versions/12/tables/0/title": "EXPLAIN labels in this source build", "/versions/12/related/1/label": "Using EXPLAIN", "/versions/12/related/2/label": "Parallel plans", "/versions/12/sections/0/title": "EXPLAIN names and attributes", "/versions/12/sections/1/title": "Memory and temporary storage", "/versions/12/sections/2/title": "Parallel execution and instrumentation", "/versions/12/sections/3/title": "Same-version manual discussion", "/versions/12/sections/4/title": "Executor implementation notes", "/versions/12/sections/5/title": "EXPLAIN identity in core source", "/versions/12/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/12/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/12/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/12/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/12/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/12/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/12/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/12/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/12/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/12/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/12/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/12/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/12/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/12/tables/0/columns/0/label": "Text-format label", "/versions/12/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "1a3b3778f0d1773131f3bea08ebcc80bacf4c6dd6fbad79d686fc4d7b3a76231"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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\u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/13/parallel-plans.html", "method": "same-major semantic node", "sha256": "bbbbbd9cc27db6811c388e9c4951a9641c48871942bc709cec203e4271518c50", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/13/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/13/facts/0/label": "Core node tag", "/versions/13/facts/1/label": "Structured EXPLAIN Node Type", "/versions/13/facts/2/label": "Inputs", "/versions/13/facts/2/value": "One ordered parallel child plan", "/versions/13/facts/3/label": "Output", "/versions/13/facts/3/value": "Merged ordered tuples", "/versions/13/facts/4/label": "Executor initializer", "/versions/13/facts/5/label": "Memory mechanism", "/versions/13/tables/0/title": "EXPLAIN labels in this source build", "/versions/13/related/1/label": "Using EXPLAIN", "/versions/13/related/2/label": "Parallel plans", "/versions/13/sections/0/title": "EXPLAIN names and attributes", "/versions/13/sections/1/title": "Memory and temporary storage", "/versions/13/sections/2/title": "Parallel execution and instrumentation", "/versions/13/sections/3/title": "Same-version manual discussion", "/versions/13/sections/4/title": "Executor implementation notes", "/versions/13/sections/5/title": "EXPLAIN identity in core source", "/versions/13/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/13/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/13/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/13/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/13/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/13/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/13/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/13/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/13/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/13/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/13/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/13/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/13/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/13/tables/0/columns/0/label": "Text-format label", "/versions/13/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "ba907fb914c962dccc2fe952635d486912b7daa1e030fd58e4567e2ec160ca92"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/14/parallel-plans.html", "method": "same-major semantic node", "sha256": "27ba0fab61ef7b5aa518b18597a7cd30f9560e5cf2b383016d31e59518892f88", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/14/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/14/facts/0/label": "Core node tag", "/versions/14/facts/1/label": "Structured EXPLAIN Node Type", "/versions/14/facts/2/label": "Inputs", "/versions/14/facts/2/value": "One ordered parallel child plan", "/versions/14/facts/3/label": "Output", "/versions/14/facts/3/value": "Merged ordered tuples", "/versions/14/facts/4/label": "Executor initializer", "/versions/14/facts/5/label": "Memory mechanism", "/versions/14/tables/0/title": "EXPLAIN labels in this source build", "/versions/14/related/1/label": "Using EXPLAIN", "/versions/14/related/2/label": "Parallel plans", "/versions/14/sections/0/title": "EXPLAIN names and attributes", "/versions/14/sections/1/title": "Memory and temporary storage", "/versions/14/sections/2/title": "Parallel execution and instrumentation", "/versions/14/sections/3/title": "Same-version manual discussion", "/versions/14/sections/4/title": "Executor implementation notes", "/versions/14/sections/5/title": "EXPLAIN identity in core source", "/versions/14/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/14/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/14/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/14/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/14/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/14/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/14/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/14/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/14/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/14/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/14/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/14/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/14/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/14/tables/0/columns/0/label": "Text-format label", "/versions/14/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "76232322a89c6dc0b12a461acb433395eea3607416cc75dd19853434459c5d9c"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/15/parallel-plans.html", "method": "same-major semantic node", "sha256": "f854eb236b7b7015acb3d4356b2199700ef6396672fbb271f4325b656c16e6c3", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/15/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/15/facts/0/label": "Core node tag", "/versions/15/facts/1/label": "Structured EXPLAIN Node Type", "/versions/15/facts/2/label": "Inputs", "/versions/15/facts/2/value": "One ordered parallel child plan", "/versions/15/facts/3/label": "Output", "/versions/15/facts/3/value": "Merged ordered tuples", "/versions/15/facts/4/label": "Executor initializer", "/versions/15/facts/5/label": "Memory mechanism", "/versions/15/tables/0/title": "EXPLAIN labels in this source build", "/versions/15/related/1/label": "Using EXPLAIN", "/versions/15/related/2/label": "Parallel plans", "/versions/15/sections/0/title": "EXPLAIN names and attributes", "/versions/15/sections/1/title": "Memory and temporary storage", "/versions/15/sections/2/title": "Parallel execution and instrumentation", "/versions/15/sections/3/title": "Same-version manual discussion", "/versions/15/sections/4/title": "Executor implementation notes", "/versions/15/sections/5/title": "EXPLAIN identity in core source", "/versions/15/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/15/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/15/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/15/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/15/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/15/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/15/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/15/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/15/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/15/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/15/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/15/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/15/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/15/tables/0/columns/0/label": "Text-format label", "/versions/15/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "061482c8bebb71484382898c335fd242cdf368c762d565e285d0c11bce1d004f"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/16/parallel-plans.html", "method": "same-major semantic node", "sha256": "ebdab5889ade652e62c92fd2e4361d8aa32ae8132faccfdcafab869292fc4392", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/16/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/16/facts/0/label": "Core node tag", "/versions/16/facts/1/label": "Structured EXPLAIN Node Type", "/versions/16/facts/2/label": "Inputs", "/versions/16/facts/2/value": "One ordered parallel child plan", "/versions/16/facts/3/label": "Output", "/versions/16/facts/3/value": "Merged ordered tuples", "/versions/16/facts/4/label": "Executor initializer", "/versions/16/facts/5/label": "Memory mechanism", "/versions/16/tables/0/title": "EXPLAIN labels in this source build", "/versions/16/related/1/label": "Using EXPLAIN", "/versions/16/related/2/label": "Parallel plans", "/versions/16/sections/0/title": "EXPLAIN names and attributes", "/versions/16/sections/1/title": "Memory and temporary storage", "/versions/16/sections/2/title": "Parallel execution and instrumentation", "/versions/16/sections/3/title": "Same-version manual discussion", "/versions/16/sections/4/title": "Executor implementation notes", "/versions/16/sections/5/title": "EXPLAIN identity in core source", "/versions/16/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/16/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/16/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/16/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/16/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/16/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/16/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/16/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/16/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/16/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/16/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/16/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/16/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/16/tables/0/columns/0/label": "Text-format label", "/versions/16/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "86b7c0bc61abc435c39eb283505ade63dc55b1ce09824cd1b1fa87b64fab3df8"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/17/parallel-plans.html", "method": "same-major semantic node", "sha256": "bc44e48acadcea02ac72779d59456e07d8600160357ceacdc258da2cbc891e23", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/17/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/17/facts/0/label": "Core node tag", "/versions/17/facts/1/label": "Structured EXPLAIN Node Type", "/versions/17/facts/2/label": "Inputs", "/versions/17/facts/2/value": "One ordered parallel child plan", "/versions/17/facts/3/label": "Output", "/versions/17/facts/3/value": "Merged ordered tuples", "/versions/17/facts/4/label": "Executor initializer", "/versions/17/facts/5/label": "Memory mechanism", "/versions/17/tables/0/title": "EXPLAIN labels in this source build", "/versions/17/related/1/label": "Using EXPLAIN", "/versions/17/related/2/label": "Parallel plans", "/versions/17/sections/0/title": "EXPLAIN names and attributes", "/versions/17/sections/1/title": "Memory and temporary storage", "/versions/17/sections/2/title": "Parallel execution and instrumentation", "/versions/17/sections/3/title": "Same-version manual discussion", "/versions/17/sections/4/title": "Executor implementation notes", "/versions/17/sections/5/title": "EXPLAIN identity in core source", "/versions/17/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/17/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/17/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/17/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/17/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/17/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/17/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/17/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/17/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/17/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/17/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/17/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/17/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/17/tables/0/columns/0/label": "Text-format label", "/versions/17/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "e1b2531457ed94c376f69168759732d8fbe07979e8f12eb2b2ea098d36d3eaf1"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/18/parallel-plans.html", "method": "same-major semantic node", "sha256": "7fa104623c0b4cd22acf0929e40518fbed8fe368af3e3b124cf693bd7ab69f0c", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/18/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/18/facts/0/label": "Core node tag", "/versions/18/facts/1/label": "Structured EXPLAIN Node Type", "/versions/18/facts/2/label": "Inputs", "/versions/18/facts/2/value": "One ordered parallel child plan", "/versions/18/facts/3/label": "Output", "/versions/18/facts/3/value": "Merged ordered tuples", "/versions/18/facts/4/label": "Executor initializer", "/versions/18/facts/5/label": "Memory mechanism", "/versions/18/tables/0/title": "EXPLAIN labels in this source build", "/versions/18/related/1/label": "Using EXPLAIN", "/versions/18/related/2/label": "Parallel plans", "/versions/18/sections/0/title": "EXPLAIN names and attributes", "/versions/18/sections/1/title": "Memory and temporary storage", "/versions/18/sections/2/title": "Parallel execution and instrumentation", "/versions/18/sections/3/title": "Same-version manual discussion", "/versions/18/sections/4/title": "Executor implementation notes", "/versions/18/sections/5/title": "EXPLAIN identity in core source", "/versions/18/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/18/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/18/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/18/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/18/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/18/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/18/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/18/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/18/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/18/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/18/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/18/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/18/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/18/tables/0/columns/0/label": "Text-format label", "/versions/18/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "7e5f2fc119f356d9e1690874d8faf212ed4bbf214530fe9d99b1b4e29b8fd808"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/19/parallel-plans.html", "method": "same-major semantic node", "sha256": "c162417a8d7d4bf4b4b79ba445207cd01020c24ca11178e13a9fa3d7d8ca8e2e", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/19/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/19/facts/0/label": "Core node tag", "/versions/19/facts/1/label": "Structured EXPLAIN Node Type", "/versions/19/facts/2/label": "Inputs", "/versions/19/facts/2/value": "One ordered parallel child plan", "/versions/19/facts/3/label": "Output", "/versions/19/facts/3/value": "Merged ordered tuples", "/versions/19/facts/4/label": "Executor initializer", "/versions/19/facts/5/label": "Memory mechanism", "/versions/19/tables/0/title": "EXPLAIN labels in this source build", "/versions/19/related/1/label": "Using EXPLAIN", "/versions/19/related/2/label": "Parallel plans", "/versions/19/sections/0/title": "EXPLAIN names and attributes", "/versions/19/sections/1/title": "Memory and temporary storage", "/versions/19/sections/2/title": "Parallel execution and instrumentation", "/versions/19/sections/3/title": "Same-version manual discussion", "/versions/19/sections/4/title": "Executor implementation notes", "/versions/19/sections/5/title": "EXPLAIN identity in core source", "/versions/19/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/19/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/19/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/19/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/19/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/19/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/19/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/19/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/19/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/19/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/19/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/19/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/19/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/19/tables/0/columns/0/label": "Text-format label", "/versions/19/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "168fdef6b3f85814a4b5456646c9cf92dd2ef2ed06ea1b159130583ac50ca687"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/devel/parallel-plans.html", "method": "same-major semantic node", "sha256": "322333100879d0971d33685d4924d0c6b79bc429a74a35f9cca60c247e02b545", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/summary": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/category": "Parallelism", "/versions/20/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/20/facts/0/label": "Core node tag", "/versions/20/facts/1/label": "Structured EXPLAIN Node Type", "/versions/20/facts/2/label": "Inputs", "/versions/20/facts/2/value": "One ordered parallel child plan", "/versions/20/facts/3/label": "Output", "/versions/20/facts/3/value": "Merged ordered tuples", "/versions/20/facts/4/label": "Executor initializer", "/versions/20/facts/5/label": "Memory mechanism", "/versions/20/tables/0/title": "EXPLAIN labels in this source build", "/versions/20/related/1/label": "Using EXPLAIN", "/versions/20/related/2/label": "Parallel plans", "/versions/20/sections/0/title": "EXPLAIN names and attributes", "/versions/20/sections/1/title": "Memory and temporary storage", "/versions/20/sections/2/title": "Parallel execution and instrumentation", "/versions/20/sections/3/title": "Same-version manual discussion", "/versions/20/sections/4/title": "Executor implementation notes", "/versions/20/sections/5/title": "EXPLAIN identity in core source", "/versions/20/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/20/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/20/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/20/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/20/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/20/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/20/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/20/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/20/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/20/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/20/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/20/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/20/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/20/tables/0/columns/0/label": "Text-format label", "/versions/20/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "1cf420bba9ed1a3d80c71c82180da06d5b414f46cd2a317dda8d08f372285a32"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": 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"62207d207bead82b01b59dc119c4f95856f08655cc11d4699a05a40867ed2070", "language": "en", "original_url": "/docs/18/parallel-plans.html#PARALLEL-AGGREGATION"}], "node_tag": "T_GatherMerge", "sections": [{"title": "EXPLAIN \u540d\u79f0\u4e0e\u5c5e\u6027", "paragraphs": ["\u7ed3\u6784\u5316\u683c\u5f0f\u4f7f\u7528\u4e0a\u8ff0 Node Type\u3002\u6587\u672c\u683c\u5f0f\u540d\u79f0\u8fd8\u53ef\u80fd\u5305\u542b\u64cd\u4f5c\u3001\u7b56\u7565\u3001\u8fde\u63a5\u7c7b\u578b\u3001\u626b\u63cf\u65b9\u5411\u6216\u805a\u5408\u9636\u6bb5\u5c5e\u6027\u3002", "\u6b64\u6e90\u7801\u8bb0\u5f55\u7684\u6587\u672c\u540d\u79f0\uff1aGather Merge.", "\u5e76\u884c\u611f\u77e5\u4e0e\u5e76\u884c\u5b89\u5168\u662f\u4e0d\u540c\u7684\u8ba1\u5212\u5c5e\u6027\u3002\u5728\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u5185\u8fd0\u884c\u7684\u8282\u70b9\u4e0d\u4e00\u5b9a\u662f\u5e76\u884c\u611f\u77e5\u8282\u70b9\u3002"]}, {"title": "\u5185\u5b58\u4e0e\u4e34\u65f6\u5b58\u50a8", "paragraphs": ["\u672c\u6b21\u62bd\u53d6\u4e0d\u4e3a\u6b64\u8282\u70b9\u8bbe\u5b9a\u7edf\u4e00\u7684\u5185\u5b58\u4e0a\u9650\u6216\u843d\u76d8\u7b56\u7565\u3002\u8bf7\u67e5\u770b\u540c\u4e00\u6784\u5efa\u7684\u5b9e\u73b0\u3001\u76f8\u5173\u8868\u8fbe\u5f0f\u6216\u63d0\u4f9b\u65b9\u3002"]}, {"title": "\u5e76\u884c\u6267\u884c\u4e0e\u8fd0\u884c\u4fe1\u606f\u91c7\u96c6", "paragraphs": ["\u4ee5\u4e0b\u6e90\u7801\u56de\u8c03\u53ef\u4ee5\u534f\u8c03\u6267\u884c\u6216\u6536\u96c6\u5de5\u4f5c\u8fdb\u7a0b\u7684\u6d4b\u91cf\u6570\u636e\u3002\u56de\u8c03\u5b58\u5728\u4e0d\u4ee3\u8868\u8be5\u8282\u70b9\u666e\u904d\u652f\u6301\u5171\u4eab\u5e76\u884c\u626b\u63cf\u6216\u5171\u4eab\u72b6\u6001\u3002", "\u6b64\u6784\u5efa\u7684\u56de\u8c03\uff1anone extracted from this node implementation."]}, {"title": "\u540c\u7248\u672c\u624b\u518c\u8bf4\u660e", "paragraphs": ["PostgreSQL \u901a\u8fc7\u5206\u4e24\u4e2a\u9636\u6bb5\u8fdb\u884c\u805a\u5408\u6765\u652f\u6301\u5e76\u884c\u805a\u5408\u3002\u9996\u5148\uff0c\u6bcf\u4e2a\u53c2\u4e0e\u67e5\u8be2\u5e76\u884c\u90e8\u5206\u7684\u8fdb\u7a0b\u6267\u884c\u4e00\u4e2a\u805a\u5408\u6b65\u9aa4\uff0c\u4e3a\u8be5\u8fdb\u7a0b\u6240\u89c1\u5230\u7684\u6bcf\u4e2a\u5206\u7ec4\u4ea7\u751f\u4e00\u4e2a\u90e8\u5206\u7ed3\u679c\u3002\u8fd9\u5728\u8ba1\u5212\u4e2d\u4f53\u73b0\u4e3a\u4e00\u4e2a Partial Aggregate \u8282\u70b9\u3002\u7136\u540e\uff0c\u90e8\u5206\u7ed3\u679c\u901a\u8fc7 Gather \u6216 Gather Merge \u4f20\u9001\u7ed9\u9886\u5bfc\u8005\u3002\u6700\u540e\uff0c\u9886\u5bfc\u8005\u4f1a\u628a\u6765\u81ea\u6240\u6709\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u518d\u6b21\u805a\u5408\uff0c\u4ee5\u4ea7\u751f\u6700\u7ec8\u7ed3\u679c\u3002\u8fd9\u5728\u8ba1\u5212\u4e2d\u4f53\u73b0\u4e3a\u4e00\u4e2a Finalize Aggregate \u8282\u70b9\u3002"]}, {"title": "\u6267\u884c\u5668\u5b9e\u73b0\u8bf4\u660e", "paragraphs": ["nodeGatherMerge.c\uff1a\u5728\u591a\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u4e2d\u626b\u63cf\u8ba1\u5212\u5e76\u4fdd\u6301\u987a\u5e8f\u5730\u5f52\u5e76\u3002", "\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u5143\u7ec4\u65f6\uff0c\u5c3d\u53ef\u80fd\u4e00\u6b21\u8bfb\u53d6\u591a\u4e2a\u53ef\u964d\u4f4e\u4e0a\u4e0b\u6587\u5207\u6362\u5f00\u9500\u3002\u4f46\u4e00\u6b21\u8bfb\u53d6\u8fc7\u591a\u4f1a\u6d6a\u8d39\u5185\u5b58\u800c\u65e0\u52a9\u4e8e\u6027\u80fd\u3002\u56e0\u6b64\u9664\u7b2c\u4e00\u4e2a\u5143\u7ec4\u5916\uff0c\u6700\u591a\u518d\u8bfb\u53d6 MAX_TUPLE_STORE \u4e2a\u3002", "\u6bcf\u4e2a\u5de5\u4f5c\u8fdb\u7a0b\u7684\u5f85\u5904\u7406\u5143\u7ec4\u6570\u7ec4\uff0c\u4fdd\u5b58\u5df2\u4ece\u5de5\u4f5c\u8fdb\u7a0b\u8bfb\u53d6\u4f46\u5c1a\u4e0d\u80fd\u5904\u7406\u7684\u989d\u5916\u5143\u7ec4\u3002\u6b64\u7ed3\u6784\u8fd8\u4fdd\u5b58 done \u6807\u5fd7\uff0c\u8868\u793a\u5df2\u77e5\u8be5\u5de5\u4f5c\u8fdb\u7a0b\u4e0d\u518d\u6709\u5143\u7ec4\u3002\uff08\u9886\u5bfc\u8fdb\u7a0b\u4e0d\u4f7f\u7528\u6b64\u7ed3\u6784\uff1a\u4e0d\u4e3a\u5176\u4fdd\u5b58\u5f85\u5904\u7406\u5143\u7ec4\uff0c\u5e76\u7528 need_to_scan_locally \u6807\u5fd7\u8868\u793a\u662f\u5426\u5b8c\u6210\u3002\uff09", "GatherMerge \u4e0d\u652f\u6301\u68c0\u67e5\u6761\u4ef6\uff0c\u56e0\u4e3a\u5728\u5b50\u8282\u70b9\u4e2d\u68c0\u67e5\u603b\u662f\u66f4\u9ad8\u6548\u3002", "\u9886\u5bfc\u8fdb\u7a0b\u53ef\u80fd\u76f4\u63a5\u8bbf\u95ee ExecProcNode \u7684\u7ed3\u679c\uff08need_to_scan_locally \u4e3a\u771f\u65f6\uff09\uff0c\u4e5f\u53ef\u80fd\u901a\u8fc7\u5143\u7ec4\u961f\u5217\u63a5\u6536\u5de5\u4f5c\u8fdb\u7a0b\u7684\u7ed3\u679c\u3002\u56e0\u6b64\uff0c\u4e0d\u80fd\u7b80\u5355\u5047\u5b9a\u5728\u6b64\u8282\u70b9\u5185\u8ba1\u7b97\u8868\u8fbe\u5f0f\u65f6\uff0c\u5143\u7ec4\u69fd\u7c7b\u578b\u59cb\u7ec8\u56fa\u5b9a\u3002"]}, {"code": "case T_GatherMerge:\n\t\t\tpname = sname = \"Gather Merge\";\n\t\t\tbreak;", "title": "\u6838\u5fc3\u6e90\u7801\u4e2d\u7684 EXPLAIN \u6807\u8bc6"}], "strategies": [], "description": ["\u5bf9\u5e76\u884c\u5de5\u4f5c\u8fdb\u7a0b\u53ca\u53c2\u4e0e\u6267\u884c\u7684\u4e3b\u8fdb\u7a0b\u4ea7\u751f\u7684\u6709\u5e8f\u5143\u7ec4\u6d41\u8fdb\u884c\u5f52\u5e76\u3002"], "localization": {"status": "complete", "sources": [{"url": "/docs/18/parallel-plans.html", "method": "same-major semantic node", "sha256": "7fa104623c0b4cd22acf0929e40518fbed8fe368af3e3b124cf693bd7ab69f0c", "language": "zh", "matched_nodes": ["#PARALLEL-PLANS/div[5]/p[1]"]}], "language": "zh", "original_text": {"/versions/18/description/0": "Merges ordered tuple streams from parallel workers and any participating leader execution.", "/versions/18/facts/0/label": "Core node tag", "/versions/18/facts/1/label": "Structured EXPLAIN Node Type", "/versions/18/facts/2/label": "Inputs", "/versions/18/facts/2/value": "One ordered parallel child plan", "/versions/18/facts/3/label": "Output", "/versions/18/facts/3/value": "Merged ordered tuples", "/versions/18/facts/4/label": "Executor initializer", "/versions/18/facts/5/label": "Memory mechanism", "/versions/18/tables/0/title": "EXPLAIN labels in this source build", "/versions/18/related/1/label": "Using EXPLAIN", "/versions/18/related/2/label": "Parallel plans", "/versions/18/sections/0/title": "EXPLAIN names and attributes", "/versions/18/sections/1/title": "Memory and temporary storage", "/versions/18/sections/2/title": "Parallel execution and instrumentation", "/versions/18/sections/3/title": "Same-version manual discussion", "/versions/18/sections/4/title": "Executor implementation notes", "/versions/18/sections/5/title": "EXPLAIN identity in core source", "/versions/18/memory/description": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/18/sections/0/paragraphs/0": "Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.", "/versions/18/sections/0/paragraphs/1": "Text names recorded by this source: Gather Merge.", "/versions/18/sections/0/paragraphs/2": "Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.", "/versions/18/sections/1/paragraphs/0": "This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.", "/versions/18/sections/2/paragraphs/0": "The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.", "/versions/18/sections/2/paragraphs/1": "Callbacks in this build: none extracted from this node implementation.", "/versions/18/sections/3/paragraphs/0": "PostgreSQL supports parallel aggregation by aggregating in two stages. First, each process participating in the parallel portion of the query performs an aggregation step, producing a partial result for each group of which that process is aware. This is reflected in the plan as a Partial Aggregate node. Second, the partial results are transferred to the leader via Gather or Gather Merge . Finally, the leader re-aggregates the results across all workers in order to produce the final result. This is reflected in the plan as a Finalize Aggregate node.", "/versions/18/sections/4/paragraphs/0": "nodeGatherMerge.c Scan a plan in multiple workers, and do order-preserving merge.", "/versions/18/sections/4/paragraphs/1": "When we read tuples from workers, it's a good idea to read several at once for efficiency when possible: this minimizes context-switching overhead. But reading too many at a time wastes memory without improving performance. We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).", "/versions/18/sections/4/paragraphs/2": "Pending-tuple array for each worker. This holds additional tuples that we were able to fetch from the worker, but can't process yet. In addition, this struct holds the \"done\" flag indicating the worker is known to have no more tuples. (We do not use this struct for the leader; we don't keep any pending tuples for the leader, and the need_to_scan_locally flag serves as its \"done\" indicator.)", "/versions/18/sections/4/paragraphs/3": "GatherMerge doesn't support checking a qual (it's always more efficient to do it in the child node).", "/versions/18/sections/4/paragraphs/4": "Leader may access ExecProcNode result directly (if need_to_scan_locally), or from workers via tuple queue. So we can't trivially rely on the slot type being fixed for expressions evaluated within this node.", "/versions/18/tables/0/columns/0/label": "Text-format label", "/versions/18/tables/0/columns/1/label": "Structured node identity"}, "fallback_fields": [], "source_language": "en", "original_snapshot_sha256": "7e5f2fc119f356d9e1690874d8faf212ed4bbf214530fe9d99b1b4e29b8fd808"}, "evidence_kind": "source and documentation", "explain_names": ["Gather Merge"], "partial_modes": [], "comparison_data": {"node_tag": "T_GatherMerge", "strategies": [], "text_names": ["Gather Merge"], "initializer": "ExecInitGatherMerge", "partial_modes": [], "memory_mechanism": "unclassified", "parallel_callbacks": []}, "comparison_hash": "7a1c97656626af0791de9743def719924b5c292f47f0634adc2b0e6e4fd2ad21", "explain_prefixes": ["Parallel", "Async"], "runtime_verified": false, "source_inventory": {"explain": "src/backend/commands/explain.c", "executor": "src/backend/executor/execProcnode.c", "implementation": "src/backend/executor/nodeGatherMerge.c"}, "parallel_callbacks": []}, "comparison": {"left": "17", "right": "18", "status": "unchanged", "diff": ""}}