LWLock/WALInsert

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. 9.6

   LWLockTranche/wal_insert曾用名

   等待将 WAL 插入内存缓冲区。

   Waiting to insert WAL into a memory buffer.

2. 10–12

   LWLock/wal_insert曾用名

   等待将 WAL 插入内存缓冲区。

   Waiting to insert WAL into a memory buffer.

3. 13–20

   LWLock/WALInsert

   等待将WAL数据插入内存缓冲区。

   Waiting to insert WAL data into a memory buffer.

触发机制

后端在共享 WAL 缓冲区中预留空间并复制 WAL 记录时，必须持有一个 WAL insertion lock。并发 WAL 生产者很多、插入临界区变长时，会在此排队。

A backend must hold one of the WAL insertion locks while reserving and copying a WAL record into shared WAL buffers. High concurrent WAL producers can queue when insertion critical sections lengthen.

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 = 'LWLock'
  AND wait_event = 'WALInsert'
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 = 'LWLock'
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 = 'LWLock'
  AND a.wait_event = 'WALInsert'
ORDER BY a.pid, l.granted, l.locktype, l.mode;

处置步骤

1. 按 WAL 生成量与调用频率排序语句。
2. 检查检查点/全页镜像时机与并发写会话数量。
3. 批量合并微小写入、减少无效索引抖动，并处理 WAL 写延迟。

相关参数与指标

wal_buffersfull_page_writescheckpoint_timeout waiting_sessionswait_event_sharewal_byteswal_fpistatement_wal_bytes

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 13 ← 12 更名

   更名 wal_insert→WALInsert 描述措辞更新

   等待将WAL数据插入内存缓冲区。

   描述前后对照

   Waiting to insert WAL into a memory buffer. Waiting to insert WAL data into a memory buffer.

2. PostgreSQL 10 ← 9.6 类型变动

   类型 LWLockTranche→LWLock

   等待将 WAL 插入内存缓冲区。

3. PostgreSQL 9.6 新增此事件

   9.6 引入等待事件机制，此为本事件的首个版本

   等待将 WAL 插入内存缓冲区。

同类事件