PostgreSQL DBA日常运维必备SQL大全

1. PostgreSQL DBA日常运维必备SQL大全

作为PostgreSQL数据库管理员，日常工作中需要频繁使用各种SQL来监控数据库状态、排查性能问题、优化资源使用。经过多年实战积累，我整理了一套非常实用的DBA常用SQL集合，涵盖了数据库监控、性能分析、资源优化等各个方面。

这些SQL大多以视图或存储过程的形式存在，可以直接在数据库中创建，方便日常调用。下面我将分类详细介绍这些SQL的使用场景和实现原理。

2. 数据库基础监控视图

2.1 无效索引检查

sql复制CREATE VIEW dba.invalid_index AS 
SELECT indisvalid, indexrelid::regclass, indrelid::regclass, pg_get_indexdef(indexrelid) 
FROM pg_index 
WHERE NOT indisvalid;

这个视图用于检查数据库中所有无效的索引。当索引被标记为无效(indisvalid=false)时，查询优化器会忽略这些索引，但它们仍然占用存储空间。定期检查并删除无效索引可以回收存储空间。

2.2 只读冲突统计

sql复制CREATE VIEW dba.ro_conflicts AS 
SELECT datname,
       pg_stat_get_db_conflict_all(oid) conflict_all,
       pg_stat_get_db_conflict_bufferpin(oid) conflict_bufferpin,
       pg_stat_get_db_conflict_lock(oid) conflict_lock,
       pg_stat_get_db_conflict_snapshot(oid) conflict_snapshot,
       pg_stat_get_db_conflict_startup_deadlock(oid) conflict_deadlock,
       pg_stat_get_db_conflict_tablespace(oid) conflict_tbs 
FROM pg_database;

该视图显示各数据库发生的冲突统计信息，包括：

• bufferpin冲突：由于缓冲区pin等待导致的冲突
• 锁冲突：由于锁等待导致的冲突
• 快照冲突：由于快照不一致导致的冲突
• 启动死锁：启动过程中的死锁
• 表空间冲突：表空间相关的冲突

高冲突率可能表明应用程序存在并发问题。

2.3 事务处理速率(TPS)监控

sql复制CREATE OR REPLACE PROCEDURE dba.tps() AS $$
DECLARE
  v1 int8;
  v2 int8;
BEGIN
  SELECT txid_snapshot_xmax(txid_current_snapshot()) INTO v1;
  COMMIT;
  PERFORM pg_sleep(1);
  SELECT txid_snapshot_xmax(txid_current_snapshot()) INTO v2;
  COMMIT;
  RAISE NOTICE 'tps: %', v2-v1;
END;
$$ LANGUAGE plpgsql;

这个存储过程通过比较1秒内事务ID的增长量来计算TPS(每秒事务数)。执行时会输出类似"NOTICE: tps: 125"的信息，表示当前TPS为125。

注意：这种方法计算的是数据库整体TPS，如果需要计算特定应用的TPS，应该使用应用层的监控指标。

3. 复制与高可用监控

3.1 主从复制延迟监控

在主节点上创建以下视图监控复制延迟：

sql复制CREATE VIEW dba.ro_delay AS 
SELECT application_name, client_addr, client_port, write_lag, replay_lag, sync_state 
FROM pg_stat_replication;

各字段含义：

• write_lag: 主库写入WAL到备库接收WAL的延迟
• replay_lag: 备库接收WAL到应用WAL的延迟
• sync_state: 复制同步状态(同步/异步)

在备节点上创建以下视图监控接收和回放延迟：

sql复制-- 检查备库replay比receive的延迟
CREATE VIEW dba.node_delay AS 
SELECT * FROM pg_size_pretty(pg_wal_lsn_diff(pg_last_wal_receive_lsn(), pg_last_wal_replay_lsn())) AS t(delay);

-- 检查备库接收WAL比主库产生WAL的延迟
CREATE VIEW dba.ro_delay_on_standby AS 
SELECT pg_size_pretty(pg_wal_lsn_diff(latest_end_lsn, received_lsn)) 
FROM pg_stat_wal_receiver;

3.2 备库WAL接收和回放带宽监控

sql复制-- 备库WAL接收带宽
CREATE OR REPLACE PROCEDURE dba.wal_receive_bw()
LANGUAGE plpgsql
AS $procedure$
DECLARE
  v1 pg_lsn;
  v2 pg_lsn;
BEGIN
  SELECT pg_last_wal_receive_lsn() INTO v1;
  COMMIT;
  PERFORM pg_sleep(1);
  SELECT pg_last_wal_receive_lsn() INTO v2;
  COMMIT;
  RAISE NOTICE 'wal receive bw: %/s', pg_size_pretty(pg_wal_lsn_diff(v2,v1));
END;
$procedure$;

-- 备库WAL回放带宽
CREATE OR REPLACE PROCEDURE dba.wal_replay_bw()
LANGUAGE plpgsql
AS $procedure$
DECLARE
  v1 pg_lsn;
  v2 pg_lsn;
BEGIN
  SELECT pg_last_wal_replay_lsn() INTO v1;
  COMMIT;
  PERFORM pg_sleep(1);
  SELECT pg_last_wal_replay_lsn() INTO v2;
  COMMIT;
  RAISE NOTICE 'wal replay bw: %/s', pg_size_pretty(pg_wal_lsn_diff(v2,v1));
END;
$procedure$;

这两个存储过程分别测量备库接收和应用WAL的速率，对于诊断复制性能问题非常有用。

4. 性能分析与SQL监控

4.1 高耗时SQL查询

sql复制CREATE VIEW dba.topsql AS 
SELECT calls, total_time, total_time/calls, query 
FROM pg_stat_statements 
WHERE query !~ 'rds' 
ORDER BY total_time DESC 
LIMIT 5;

此视图显示总耗时最高的5条SQL，基于pg_stat_statements扩展收集的统计信息。字段包括：

• calls: 执行次数
• total_time: 总耗时(毫秒)
• total_time/calls: 平均耗时
• query: SQL文本

注意：使用前需确保已安装pg_stat_statements扩展并正确配置。

4.2 QPS(每秒查询数)监控

sql复制CREATE VIEW dba.qps AS 
WITH a AS (SELECT sum(calls) s FROM pg_stat_statements),
     b AS (SELECT sum(calls) s FROM pg_stat_statements, pg_sleep(1))
SELECT b.s-a.s AS qps FROM a,b;

这个视图通过比较1秒前后SQL执行总数的差值来计算QPS。

4.3 活跃会话监控

sql复制-- 活跃会话数
CREATE VIEW dba.session_acting_cnt AS 
SELECT count(*) 
FROM pg_stat_activity 
WHERE wait_event IS NOT NULL 
AND (backend_xid IS NOT NULL OR backend_xmin IS NOT NULL);

-- 活跃会话详情
CREATE VIEW dba.sessions AS 
SELECT * 
FROM pg_stat_activity 
WHERE wait_event IS NOT NULL 
AND (backend_xid IS NOT NULL OR backend_xmin IS NOT NULL);

活跃会话数如果持续超过CPU核心数，说明数据库负载较高，可能需要优化。

4.4 锁等待分析

sql复制CREATE VIEW dba.locks AS 
WITH t_wait AS (
  SELECT a.mode, a.locktype, a.database, a.relation, a.page, a.tuple, a.classid, a.granted,
         a.objid, a.objsubid, a.pid, a.virtualtransaction, a.virtualxid, a.transactionid, a.fastpath,
         b.state, b.query, b.xact_start, b.query_start, b.usename, b.datname, b.client_addr, b.client_port, b.application_name
  FROM pg_locks a, pg_stat_activity b