# Timeout: VacuumTruncate

> 等待获取独占锁，以截去正在执行 vacuum 的表末尾所有空页。
---

<div class="event-kicker">PostgreSQL 等待事件档案</div>
<div class="event-identity">
  <span>类别<strong>Timeout</strong></span>
  <span>事件<strong><code>VacuumTruncate</code></strong></span>
  <span>版本<strong>PG 15-18</strong></span>
  <span>证据<strong>2 个源码位置</strong></span>
</div>

## 官方描述译文 {#official-description}

等待获取独占锁，以截去正在执行 vacuum 的表末尾所有空页。

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

## 触发机制 {#mechanism}

`WAIT_EVENT_VACUUM_TRUNCATE` 位于 `src/backend/access/heap/vacuumlazy.c:3280`，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:183`。探针覆盖的操作是：等待获取独占锁，以截去正在执行 vacuum 的表末尾所有空页。VacuumTruncate 路径有意等待计时器、重试间隔、节流或安全退避；latch 超时后才重新评估工作。

## 正常还是麻烦？ {#normal-vs-trouble}

- <span class="severity-normal">**正常:**</span> 当配置策略是有意的，而且有效工作按预期速率推进时，这项等待正常。
- <span class="severity-watch">**需要调查:**</span> 策略导致维护、恢复、备份或延迟目标无法达成，或者 spin delay 持续时，应当调查。

## 诊断 SQL {#diagnostic-sql}

```sql {title="正在等待 Timeout/VacuumTruncate 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 = 'Timeout'
  AND wait_event = 'VacuumTruncate'
ORDER BY query_age DESC NULLS LAST;
```

```sql {title="当前 Timeout 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 = 'Timeout'
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 = 'Timeout'
  AND a.wait_event = 'VacuumTruncate'
ORDER BY a.pid, l.granted, l.locktype, l.mode;
```

## 处置建议 {#response}

1. 确认拥有该计时器的 GUC 或函数。
2. 比较有效工作量与延迟时间。
3. 先检查它原本要控制的 CPU、I/O 与持久性压力，再调整策略。

## 源码证据 {#source}

- [PostgreSQL 18.6 · src/backend/access/heap/vacuumlazy.c:3280](https://github.com/postgres/postgres/blob/REL_18_6/src/backend/access/heap/vacuumlazy.c#L3280) — `WAIT_EVENT_VACUUM_TRUNCATE`
- [PostgreSQL 18.6 · src/backend/utils/activity/wait_event_names.txt:183](https://github.com/postgres/postgres/blob/REL_18_6/src/backend/utils/activity/wait_event_names.txt#L183) — `VACUUM_TRUNCATE`

## 关联控制项与信号 {#related}

- **GUC:** [[guc:autovacuum_naptime]](/zh/guc/autovacuum-naptime/)
- **指标:** [[metric:waiting_sessions]](/zh/metric/waiting-sessions/) · [[metric:wait_event_share]](/zh/metric/wait-event-share/) · [[metric:oldest_transaction_age]](/zh/metric/oldest-transaction-age/)