這篇文章主要講解了“分析PostgreSQL DBA中新增的WAL選項(xiàng)”,文中的講解內(nèi)容簡(jiǎn)單清晰,易于學(xué)習(xí)與理解,下面請(qǐng)大家跟著小編的思路慢慢深入,一起來(lái)研究和學(xué)習(xí)“分析PostgreSQL DBA中新增的WAL選項(xiàng)”吧!
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在PG 13中,explain命令增加了WAL選項(xiàng),可查看命令執(zhí)行過(guò)程中產(chǎn)生的WAL日志大小,對(duì)于寫(xiě)敏感的應(yīng)用來(lái)說(shuō),可通過(guò)該命令觀(guān)察WAL日志的統(tǒng)計(jì)信息.
新增的WAL選項(xiàng)
[local:/data/run/pg13]:5130 pg13@masterdb=# \help explain Command: EXPLAIN Description: show the execution plan of a statement Syntax: EXPLAIN [ ( option [, ...] ) ] statement EXPLAIN [ ANALYZE ] [ VERBOSE ] statement where option can be one of: ANALYZE [ boolean ] VERBOSE [ boolean ] COSTS [ boolean ] SETTINGS [ boolean ] BUFFERS [ boolean ] WAL [ boolean ] TIMING [ boolean ] SUMMARY [ boolean ] FORMAT { TEXT | XML | JSON | YAML } URL: https://www.postgresql.org/docs/devel/sql-explain.html [local:/data/run/pg13]:5130 pg13@masterdb=#
試用體驗(yàn)
執(zhí)行checkpoint后運(yùn)行SQL,WAL日志會(huì)寫(xiě)full page
[local:/data/run/pg13]:5130 pg13@masterdb=# checkpoint; CHECKPOINT [local:/data/run/pg13]:5130 pg13@masterdb=# explain (analyze,wal) update tmp set id = 1; QUERY PLAN ----------------------------------------------------------------------------------------------- ----------------------- Update on tmp (cost=0.00..23275.00 rows=1000000 width=10) (actual time=1636.839..1636.839 row s=0 loops=1) WAL: records=1999840 full page writes=8851 bytes=172345779 -> Seq Scan on tmp (cost=0.00..23275.00 rows=1000000 width=10) (actual time=4.686..100.211 rows=1000000 loops=1) Planning Time: 0.149 ms Execution Time: 1636.923 ms (5 rows)
再次執(zhí)行SQL,沒(méi)有寫(xiě)full page,日志大小相應(yīng)的減少
[local:/data/run/pg13]:5130 pg13@masterdb=# explain (analyze,wal) update tmp set id = 1; QUERY PLAN ----------------------------------------------------------------------------------------------- ---------------------- Update on tmp (cost=0.00..23275.00 rows=1000000 width=10) (actual time=3661.261..3661.261 row s=0 loops=1) WAL: records=1999719 bytes=131982016 -> Seq Scan on tmp (cost=0.00..23275.00 rows=1000000 width=10) (actual time=3.920..98.921 rows=1000000 loops=1) Planning Time: 0.088 ms Execution Time: 3661.310 ms (5 rows)
節(jié)省23%的空間,38KB大小
[local:/data/run/pg13]:5130 pg13@masterdb=# select (172345779-131982016)/172345779::float; ?column? --------------------- 0.23420221391090756 (1 row) [local:/data/run/pg13]:5130 pg13@masterdb=# select (172345779-131982016)/1024/1024; ?column? ---------- 38 (1 row)
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