# Lock: applytransaction

> 等待获取逻辑复制订阅端正在应用的远程事务上的锁。
---

<div class="event-kicker">PostgreSQL 等待事件档案</div>
<div class="event-identity">
  <span>类别<strong>Lock</strong></span>
  <span>事件<strong><code>applytransaction</code></strong></span>
  <span>版本<strong>PG 16-18</strong></span>
  <span>证据<strong>3 个源码位置</strong></span>
</div>

## 官方描述译文 {#official-description}

等待获取逻辑复制订阅端正在应用的远程事务上的锁。

| PG 13 | PG 14 | PG 15 | PG 16 | PG 17 | PG 18 |
| :---: | :---: | :---: | :---: | :---: | :---: |
| — | — | — | ✓ | ✓ | ✓ |

## 触发机制 {#mechanism}

`PG_WAIT_LOCK` 位于 `src/backend/storage/lmgr/proc.c:1487`，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:429`。探针覆盖的操作是：等待获取逻辑复制订阅端正在应用的远程事务上的锁。锁管理器无法立即授予 applytransaction 重量级锁；ProcSleep 报告等待，并把后端挂到该锁的等待队列，直到持有者释放或请求被取消。

## 正常还是麻烦？ {#normal-vs-trouble}

- <span class="severity-normal">**正常:**</span> 普通写入或计划内 DDL 的亚秒级锁交接可能正常。
- <span class="severity-watch">**需要调查:**</span> 面向用户的等待超过延迟目标、阻塞链持续增长，或根持有者处于 idle in transaction 时，应当调查。

## 诊断 SQL {#diagnostic-sql}

```sql {title="正在等待 Lock/applytransaction 的会话"}
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 = 'Lock'
  AND wait_event = 'applytransaction'
ORDER BY query_age DESC NULLS LAST;
```

```sql {title="当前 Lock 等待分布"}
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 = 'Lock'
GROUP BY wait_event
ORDER BY waiting_sessions DESC, wait_event;
```

```sql {title="这些会话的锁与关系上下文"}
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 = 'Lock'
  AND a.wait_event = 'applytransaction'
ORDER BY a.pid, l.granted, l.locktype, l.mode;
```

## 处置建议 {#response}

1. 沿 pg_blocking_pids 构建到根节点的阻塞图。
2. 检查根持有者状态、事务年龄与业务目的。
3. 确认最安全的根动作后，再选择取消、超时或调整负载顺序。

## 源码证据 {#source}

- [PostgreSQL 18.6 · src/backend/storage/lmgr/proc.c:1487](https://github.com/postgres/postgres/blob/REL_18_6/src/backend/storage/lmgr/proc.c#L1487) — `PG_WAIT_LOCK`
- [PostgreSQL 18.6 · src/backend/utils/activity/wait_event_names.txt:429](https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L429) — `applytransaction`
- [PostgreSQL 18.6 · src/backend/utils/adt/lockfuncs.c:40](https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/adt/lockfuncs.c#L40) — `applytransaction`

## 关联控制项与信号 {#related}

- **GUC:** [[guc:lock_timeout]](/zh/guc/lock-timeout/) · [[guc:deadlock_timeout]](/zh/guc/deadlock-timeout/)
- **指标:** [[metric:waiting_sessions]](/zh/metric/waiting-sessions/) · [[metric:wait_event_share]](/zh/metric/wait-event-share/) · [[metric:blocked_sessions]](/zh/metric/blocked-sessions/) · [[metric:locks_per_backend]](/zh/metric/locks-per-backend/)