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45.3. pg_am
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45.3. pg_am #

目录pg_am存储关于索引访问方法的信息。系统支持的每种索引访问方法在这个目录中都有一行。此目录的内容在第 52 章中详细讨论。

表 45.3. pg_am 列

Name Type References Description
amname name   Name of the access method
amstrategies int2   Number of operator strategies for this access method, or zero if access method does not have a fixed set of operator strategies
amsupport int2   Number of support routines for this access method
amcanorder bool   Does the access method support ordered scans sorted by the indexed column's value?
amcanorderbyop bool   Does the access method support ordered scans sorted by the result of an operator on the indexed column?
amcanbackward bool   Does the access method support backward scanning?
amcanunique bool   Does the access method support unique indexes?
amcanmulticol bool   Does the access method support multicolumn indexes?
amoptionalkey bool   Does the access method support a scan without any constraint for the first index column?
amsearcharray bool   访问方法是否支持ScalarArrayOpExpr搜索？
amsearchnulls bool   Does the access method support IS NULL/NOT NULL searches?
amstorage bool   Can index storage data type differ from column data type?
amclusterable bool   Can an index of this type be clustered on?
ampredlocks bool   Does an index of this type manage fine-grained predicate locks?
amkeytype oid pg_type.oid Type of data stored in index, or zero if not a fixed type
aminsert regproc pg_proc.oid “Insert this tuple” function
ambeginscan regproc pg_proc.oid “Prepare for index scan” function
amgettuple regproc pg_proc.oid “Next valid tuple” function, or zero if none
amgetbitmap regproc pg_proc.oid “Fetch all valid tuples” function, or zero if none
amrescan regproc pg_proc.oid “(Re)start index scan” function
amendscan regproc pg_proc.oid “Clean up after index scan” function
ammarkpos regproc pg_proc.oid “Mark current scan position” function
amrestrpos regproc pg_proc.oid “Restore marked scan position” function
ambuild regproc pg_proc.oid “Build new index” function
ambuildempty regproc pg_proc.oid “Build empty index” function
ambulkdelete regproc pg_proc.oid Bulk-delete function
amvacuumcleanup regproc pg_proc.oid Post-VACUUM cleanup function
amcanreturn regproc pg_proc.oid 检查索引列是否支持仅索引扫描的函数。如果从不支持仅索引扫描，可以为零。
amcostestimate regproc pg_proc.oid Function to estimate cost of an index scan
amoptions regproc pg_proc.oid Function to parse and validate reloptions for an index

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