IO/RelationMapWrite

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. 10–20

   IO/RelationMapWrite

   等待对关系映射文件的写入。

   Waiting for a write to the relation map file.

触发机制

WAIT_EVENT_RELATION_MAP_WRITE 位于 src/backend/utils/cache/relmapper.c:939，是经 grep 核验的报告路径。公共身份/资源映射位于 src/backend/utils/activity/wait_event_names.txt:238。探针覆盖的操作是：等待向 relation map 文件写入数据。PostgreSQL 在 RelationMapWrite 所表示的文件或异步 I/O 操作周围报告此事件；内核、存储栈或 I/O worker 完成该步骤后，后端继续执行。

WAIT_EVENT_RELATION_MAP_WRITE at src/backend/utils/cache/relmapper.c:939 is the grep-verified reporting path. The public identity/resource is mapped at src/backend/utils/activity/wait_event_names.txt:238. The instrumented operation is: Waiting for a write to the relation map file. PostgreSQL reports RelationMapWrite around the instrumented file or asynchronous-I/O operation named by this event. The backend resumes after the kernel, storage stack, or I/O worker completes that step.

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 = 'RelationMapWrite'
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 = 'RelationMapWrite'
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

waiting_sessionswait_event_shareio_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 10 ← 9.6 新增此事件

   该版起出现

   等待对关系映射文件的写入。

同类事件