IO/LogicalSubxactWrite

各版本描述

相邻版本里类型、名称与英文描述都相同的合并成一段，旧的在前。中文取自图谱或本站手册译文，没有译文的只给英文原文。

1. 14

   IO/LogicalSubxactWrite

   等待向逻辑子事务文件写入数据。

   Waiting for a write to a logical subxact file.

触发机制

目录中仍保留该身份，但源码审计确认在 14 已没有活动报告点。已知曾可触发范围：none。下方定义位置作为负面证据保留；当前精确版本不会从核心代码路径发出此事件。 证据：[pgsql-hackers confirmation](https://www.postgresql.org/message-id/ff077840-3ab2-04dd-bbe4-4f5dfd2ad481%40oss.nttdata.com)。

The catalog identity is present, but source audit found no live reporter in 14. Known active ranges: none. The definition location below is retained as negative evidence; this exact release cannot emit the event from a core code path. Evidence: [pgsql-hackers confirmation](https://www.postgresql.org/message-id/ff077840-3ab2-04dd-bbe4-4f5dfd2ad481%40oss.nttdata.com).

诊断 SQL

直接在 psql 里跑；标注的是语句里用到的视图与列所要求的最低版本。

SELECT pid, backend_type, usename, datname, application_name,
       state, now() - query_start AS query_age,
       now() - xact_start AS xact_age,
       wait_event_type, wait_event,
       pg_blocking_pids(pid) AS blocking_pids,
       left(query, 160) AS query
FROM pg_stat_activity
WHERE wait_event_type = 'IO'
  AND wait_event = 'LogicalSubxactWrite'
ORDER BY query_age DESC NULLS LAST;

SELECT wait_event, count(*) AS waiting_sessions,
       count(*) FILTER (WHERE state = 'active') AS active_waiters,
       max(now() - query_start) AS oldest_query
FROM pg_stat_activity
WHERE wait_event_type = 'IO'
GROUP BY wait_event
ORDER BY waiting_sessions DESC, wait_event;

SELECT a.pid, l.locktype, l.mode, l.granted, l.fastpath,
       d.datname, n.nspname, c.relname,
       l.page, l.tuple, l.virtualxid, l.transactionid,
       l.classid, l.objid, l.objsubid
FROM pg_stat_activity AS a
LEFT JOIN pg_locks AS l ON l.pid = a.pid
LEFT JOIN pg_database AS d ON d.oid = l.database
LEFT JOIN pg_class AS c
  ON c.oid = l.relation
 AND l.database = (
       SELECT oid FROM pg_database WHERE datname = current_database()
     )
LEFT JOIN pg_namespace AS n ON n.oid = c.relnamespace
WHERE a.wait_event_type = 'IO'
  AND a.wait_event = 'LogicalSubxactWrite'
ORDER BY a.pid, l.granted, l.locktype, l.mode;

处置步骤

1. 确认当前负载阶段本来就应访问这类文件。
2. 在可用版本上关联 pg_stat_io 与具体设备延迟。
3. 先修复访问路径、突发形状或受影响存储层，再调整无关的内存参数。

相关参数与指标

autovacuum_freeze_max_agevacuum_freeze_table_age waiting_sessionswait_event_shareoldest_transaction_ageio_read_timeio_write_time

源码证据

图谱在各版本源码树里核对到的位置，新的在前。「触发点」是真正上报等待事件的调用处，「目录定义」只说明这个名字在枚举里存在。

演化历史

相邻两个大版本之间的差异，新的在前。版本号链到该版的变动清单。

1. PostgreSQL 15 ← 14 移除此事件

   该版起不再存在

2. PostgreSQL 14 ← 13 新增此事件

   该版起出现

   等待向逻辑子事务文件写入数据。

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