PG数据库如何检查膨胀的表和索引

栏目：云苍穹知识作者：金蝶来源：金蝶云社区发布：2024-09-23浏览：1

PG数据库如何检查膨胀的表和索引

一检查表膨胀

select

to_char(now(),'yyyy-mm-dd hh24:mi:ss') "time"

,current_database() current_database

,relname as "table_name(表名)"

,schemaname as "schema_name(模式名)"

,pg_size_pretty(pg_relation_size('"'||schemaname|| '"."'||relname||'"')) as "table_size(表大小)"

,n_dead_tup as "n_dead_tup(无效记录数)"

,n_live_tup as "n_live_tup(有效记录数)"

,to_char(round(n_dead_tup*1.0/(n_live_tup+n_dead_tup)*100,2),'fm990.00') as "dead_rate(无效记录比例%)"

from

pg_stat_all_tables

where n_live_tup+n_dead_tup <> 0 ;

正常不存在表膨胀，因为有自动清理垃圾的进程。

异常处理，对膨胀表做vacuum analyze操作。

二检查索引膨胀

select to_char(now(),'yyyy-mm-dd hh24:mi:ss') "time", current_database() AS db, schemaname, tablename,bs, reltuples::bigint AS tups, relpages::bigint AS pages, otta, ROUND(CASE WHEN otta=0 OR sml.relpages=0 OR sml.relpages=otta THEN 0.0 ELSE sml.relpages/otta::numeric END,1) AS tbloat, CASE WHEN relpages < otta THEN 0 ELSE relpages::bigint - otta END AS wastedpages, CASE WHEN relpages < otta THEN 0 ELSE bs*(sml.relpages-otta)::bigint END AS wastedbytes, CASE WHEN relpages < otta THEN $$0 bytes$$::text ELSE (bs*(relpages-otta))::bigint || $$ bytes$$ END AS wastedsize, iname, ituples::bigint AS itups, ipages::bigint AS ipages, iotta, ROUND(CASE WHEN iotta=0 OR ipages=0 OR ipages=iotta THEN 0.0 ELSE ipages/iotta::numeric END,1) AS ibloat, CASE WHEN ipages < iotta THEN 0 ELSE ipages::bigint - iotta END AS wastedipages, CASE WHEN ipages < iotta THEN 0 ELSE bs*(ipages-iotta) END AS wastedibytes, CASE WHEN ipages < iotta THEN $$0 bytes$$ ELSE (bs*(ipages-iotta))::bigint || $$ bytes$$ END AS wastedisize, CASE WHEN relpages < otta THEN CASE WHEN ipages < iotta THEN 0 ELSE bs*(ipages-iotta::bigint) END ELSE CASE WHEN ipages < iotta THEN bs*(relpages-otta::bigint) ELSE bs*(relpages-otta::bigint + ipages-iotta::bigint) END END AS totalwastedbytesFROM ( SELECT nn.nspname AS schemaname, cc.relname AS tablename, COALESCE(cc.reltuples,0) AS reltuples, COALESCE(cc.relpages,0) AS relpages, COALESCE(bs,0) AS bs, COALESCE(CEIL((cc.reltuples*((datahdr+ma- (CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))/(bs-20::float)),0) AS otta, COALESCE(c2.relname,$$?$$) AS iname, COALESCE(c2.reltuples,0) AS ituples, COALESCE(c2.relpages,0) AS ipages, COALESCE(CEIL((c2.reltuples*(datahdr-12))/(bs-20::float)),0) AS iotta -- very rough approximation, assumes all cols FROM pg_class cc JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname <> $$information_schema$$ LEFT JOIN ( SELECT ma,bs,foo.nspname,foo.relname, (datawidth+(hdr+ma-(case when hdr%ma=0 THEN ma ELSE hdr%ma END)))::numeric AS datahdr, (maxfracsum*(nullhdr+ma-(case when nullhdr%ma=0 THEN ma ELSE nullhdr%ma END))) AS nullhdr2 FROM ( SELECT ns.nspname, tbl.relname, hdr, ma, bs, SUM((1-coalesce(null_frac,0))*coalesce(avg_width, 2048)) AS datawidth, MAX(coalesce(null_frac,0)) AS maxfracsum, hdr+( SELECT 1+count(*)/8 FROM pg_stats s2 WHERE null_frac<>0 AND s2.schemaname = ns.nspname AND s2.tablename = tbl.relname ) AS nullhdr FROM pg_attribute att JOIN pg_class tbl ON att.attrelid = tbl.oid JOIN pg_namespace ns ON ns.oid = tbl.relnamespace LEFT JOIN pg_stats s ON s.schemaname=ns.nspname AND s.tablename = tbl.relname AND s.inherited=false AND s.attname=att.attname, ( SELECT (SELECT current_setting($$block_size$$)::numeric) AS bs, CASE WHEN SUBSTRING(SPLIT_PART(v, $$ $$, 2) FROM $$#"[0-9]+.[0-9]+#"%$$ for $$#$$) IN ($$8.0$$,$$8.1$$,$$8.2$$) THEN 27 ELSE 23 END AS hdr, CASE WHEN v ~ $$mingw32$$ OR v ~ $$64-bit$$ THEN 8 ELSE 4 END AS ma FROM (SELECT version() AS v) AS foo ) AS constants WHERE att.attnum > 0 AND tbl.relkind=$$r$$ GROUP BY 1,2,3,4,5 ) AS foo ) AS rs ON cc.relname = rs.relname AND nn.nspname = rs.nspname LEFT JOIN pg_index i ON indrelid = cc.oid LEFT JOIN pg_class c2 ON c2.oid = i.indexrelid) AS sml ;

索引膨胀依赖于统计信息。统计信息未更新，索引膨胀信息不准确。一般每年统一做一次重建索引即可。

异常处理，重建索引。

reindex index 索引名；