Re: Why would a scan take so long?
От | Satoshi Nagayasu |
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Тема | Re: Why would a scan take so long? |
Дата | |
Msg-id | 2142884826-1286260582-cardhu_decombobulator_blackberry.rim.net-980892208-@bda007.bisx.prodap.on.blackberry обсуждение исходный текст |
Ответ на | Why would a scan take so long? (Michal Politowski <mpol+pg@meep.pl>) |
Список | pgsql-general |
These three queries may help you to understand what's going on. EXPLAIN ANALYZE SELECT count(catalog.id) FROM catalog; EXPLAIN ANALYZE SELECT count(catalog.id) FROM catalog WHERE flag=false; EXPLAIN ANALYZE SELECT count(DISTINCT catalog.id) FROM catalog WHERE flag=false; Regards, -- NAGAYASU Satoshi <satoshi.nagayasu@gmail.com> ------元のメッセージ------ 送信者 : Michal Politowski 送信者: pgsql-general-owner@postgresql.org To: pgsql-general@postgresql.org 件名: [GENERAL] Why would a scan take so long? 送信: 2010/10/2 12:13 AM EXPLAIN SELECT count(DISTINCT catalog.id) FROM catalog WHERE flag=false; QUERY PLAN ----------------------------------------------------------------------------------------- Aggregate (cost=1615927.27..1615927.28 rows=1 width=8) -> Seq Scan on catalog (cost=0.00..1603214.56 rows=5085084 width=8) Filter: (NOT flag) SELECT pg_size_pretty(pg_relation_size('catalog')); pg_size_pretty ---------------- 9380 MB Nothing else is going on the system, during the query disk reads rise from around 0 to > 100MB/s, so I would assume it should take a couple minutes and it takes ten times longer: Time: 1495549.716 ms What am I missing? -- Michal Politowski -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
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