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文章目录
- 1.介绍
- 2.语法
- 3.实用的使用方法
- 3.1 慢sql监控
- 3.2 长wait事件
- 3.3 日志输出量
- 3.3结合pg_stat_database使用
- 3.4 结合pg_stat_bgwriter使用
- 3.5 其他
1.介绍
\watch Postgres 9.3 版带来的一个有用的命令，与linux watch指令类似，可以帮我们在指定间隔时间内持续观察db活动，如单位时间内的事务数，commit、rollback量、刷脏量、读写量、xlog写入量、长会话、wait等
2.语法
\watch [ seconds ]
\watch 不需要在每次执行查询时获取新连接，从而节省了一些执行开销。 此外，如果查询失败，\watch会自动停止。
注意， \watch 只能在要运行的查询末尾使用。
postgres=# postgres=# \watch 2 "SELECT 1"
ERROR: syntax error at or near "postgres"
LINE 1: postgres=# ^
\watch: extra argument ""SELECT 1"" ignored
正确的使用方法
postgres=# select 1; \watch 1; ?column?
----------1
如果未指定查询语句，它将使用缓冲区中最后的查询语句。
postgres=\watch 1;
Fri 18 Aug 2023 11:34:18 AM WIB (every 1s)?column?
----------1
3.实用的使用方法
3.1 慢sql监控
postgres=select query,wait_event_type,wait_event from pg_stat_activity
where wait_event is not null and now()-state_change>interval '5 second';
ostgres=#\watch 1
3.2 长wait事件
postgres=select query,wait_event_type,wait_event from pg_stat_activity where state='active' and wait_event is not null and now()-state_change>interval '5 second';
ostgres=#\watch
3.3 日志输出量
postgres=with wal_cte as (select pg_current_wal_lsn() last_wal_lsn), sleep_cte as (select pg_sleep(1)) SELECT pg_size_pretty(pg_wal_lsn_diff(pg_current_wal_lsn(),last_wal_lsn)) from wal_cte,sleep_cte;
ostgres=#\watch 0.000001
3.3结合pg_stat_database使用
可以结合pg_stat_database 了解block命中情况、insert、update、update情况，以及temp写入情况等等
先看一下，pg_stat_database有哪些字段
commondb=# \d pg_stat_database;View "pg_catalog.pg_stat_database"Column | Type | Collation | Nullable | Default
----------------+--------------------------+-----------+----------+---------datid | oid | | | datname | name | | | numbackends | integer | | | xact_commit | bigint | | | xact_rollback | bigint | | | blks_read | bigint | | | blks_hit | bigint | | | tup_returned | bigint | | | tup_fetched | bigint | | | tup_inserted | bigint | | | tup_updated | bigint | | | tup_deleted | bigint | | | conflicts | bigint | | | temp_files | bigint | | | temp_bytes | bigint | | | deadlocks | bigint | | | blk_read_time | double precision | | | blk_write_time | double precision | | | stats_reset | timestamp with time zone | | |
postgres=\c commondb
commondb=select pg_stat_reset();pg_stat_reset
---------------(1 row)
commondb=select datid,datname,pg_size_pretty(blks_read*8192) blks_read,pg_size_pretty(blks_hit*8192) blks_hit,round(blks_hit/(blks_read+blks_hit),2) hit_ratio from pg_stat_database where datname='commondb';datid | datname | blks_read | blks_hit | hit_ratio
--------+----------+-----------+----------+-----------525340 | commondb | 0 bytes | 1259 MB | 1.00
3.4 结合pg_stat_bgwriter使用
可以结合pg_stat_database分别了解checkpoint、bgwriter、backend三个进程完成的刷脏量
postgres=\c commondb
commondb=select pg_stat_reset();pg_stat_reset
---------------(1 row)
commondb=select checkpoints_timed,
checkpoints_req,
checkpoint_write_time,
checkpoint_sync_time,
buffers_checkpoint,
round(buffers_checkpoint/(buffers_checkpoint+buffers_clean+buffers_backend )::decimal,2) ratio_checkpoint,
buffers_clean,
round(buffers_clean/(buffers_checkpoint+buffers_clean+buffers_backend )::decimal,2) ratio_bgwriter,
buffers_backend,
round(buffers_backend/(buffers_checkpoint+buffers_clean+buffers_backend )::decimal,2) ratio_checkpoint
from pg_stat_bgwriter;
checkpoints_timed | checkpoints_req | checkpoint_write_time | checkpoint_sync_time | buffers_checkpoint | ratio_checkpoint | buffers_clean | ratio_bgwriter | buffers_backend | ratio_checkpoint
-------------------+-----------------+-----------------------+----------------------+--------------------+------------------+---------------+----------------+-----------------+------------------4812 | 35 | 367777342 | 3289494 | 10630385 | 0.32 | 10245413 | 0.30 | 12763415 | 0.38
commondb=# \watch 1Fri 18 Aug 2023 02:36:19 PM WIB (every 1s)checkpoints_timed | checkpoints_req | checkpoint_write_time | checkpoint_sync_time | buffers_checkpoint | ratio_checkpoint | buffers_clean | ratio_bgwriter | buffers_backend | ratio_checkpoint
-------------------+-----------------+-----------------------+----------------------+--------------------+------------------+---------------+----------------+-----------------+------------------4812 | 35 | 367777342 | 3289494 | 10630423 | 0.32 | 10245413 | 0.30 | 12763418 | 0.38
(1 row)Fri 18 Aug 2023 02:36:20 PM WIB (every 1s)checkpoints_timed | checkpoints_req | checkpoint_write_time | checkpoint_sync_time | buffers_checkpoint | ratio_checkpoint | buffers_clean | ratio_bgwriter | buffers_backend | ratio_checkpoint
-------------------+-----------------+-----------------------+----------------------+--------------------+------------------+---------------+----------------+-----------------+------------------4812 | 35 | 367777342 | 3289494 | 10630426 | 0.32 | 10245413 | 0.30 | 12763418 | 0.38
(1 row)
3.5 其他
当然也可以与pg_stat_statements、pg_statio_user_tables查看与query语句，table有关的情况，这里只抛砖引玉，希望能够举一反三