查看执行计划

explain analyze verbose select * from t2,t3 where t2.n1=t3.n2;

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QUERY PLAN                                                            ----------------------------------------------------------------------------------------------------------------------------------  Merge Join  (cost=85.58..257.60 rows=6950 width=82) (actual time=0.029..0.031 rows=1 loops=1)    Output: t2.n1, t3.n2    Merge Cond: (t2.n1 = (t3.n2)::bpchar)    ->  Index Only Scan using idx_t2 on public.t2  (cost=0.15..65.10 rows=1130 width=44) (actual time=0.013..0.014 rows=1 loops=1)          Output: t2.n1          Heap Fetches: 1    ->  Sort  (cost=85.43..88.50 rows=1230 width=38) (actual time=0.011..0.011 rows=2 loops=1)          Output: t3.n2          Sort Key: t3.n2 USING <          Sort Method: quicksort  Memory: 25kB          ->  Seq Scan on public.t3  (cost=0.00..22.30 rows=1230 width=38) (actual time=0.004..0.005 rows=2 loops=1)                Output: t3.n2  Planning Time: 0.078 ms  Execution Time: 0.049 ms (14 rows)

　　

analyze 实际执行一次语句

verbose 是否显示详细信息

 

收集统计信息

analyze t2;

\x

postgres=# select * from pg_stats where tablename='t2';
-[ RECORD 1 ]----------+-------
schemaname | public
tablename | t2
attname | n1
inherited | f
null_frac | 0
avg_width | 11
n_distinct | -1
most_common_vals |
most_common_freqs |
histogram_bounds |
correlation |
most_common_elems |
most_common_elem_freqs |
elem_count_histogram |

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postgres=# select * from pg_stat_user_tables where relname='t2'; -[ RECORD 1 ]-------+------------------------------ relid               | 24627 schemaname          | public relname             | t2 seq_scan            | 1 seq_tup_read        | 0 idx_scan            | 4 idx_tup_fetch       | 4 n_tup_ins           | 1 n_tup_upd           | 0 n_tup_del           | 0 n_tup_hot_upd       | 0 n_live_tup          | 1 n_dead_tup          | 0 n_mod_since_analyze | 0 last_vacuum         | last_autovacuum     | last_analyze        | 2023-03-27 18:17:12.591177+08 last_autoanalyze    | vacuum_count        | 0 autovacuum_count    | 0 analyze_count       | 1 autoanalyze_count   | 0

　　设置抓取慢日志

pg 参数设置途径：1、修改postgresql.conf  2、通过alter system 修改，alter system 写入postgresql.auto.conf文件中，此文件启动时会在postgresql.conf后加载

alter system set log_statement='all';

alter system set log_min_duration_statement=5000;

重启pg  pg_ctl restart

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postgres=# show log_statement; 2023-03-28 09:50:30.849 CST [4002] LOG:  statement: show log_statement;  log_statement ---------------  all (1 row)   postgres=# show log_min_duration_statement; 2023-03-28 09:50:41.863 CST [4002] LOG:  statement: show log_min_duration_statement;  log_min_duration_statement ----------------------------  5s (1 row)

　查看当前正在执行的慢sql

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1 2	postgres=# select * from pg_stat_activity where state<>'idle' and now()-query_start > interval '5 s' order by query_start ; (0 rows)