Re: Timestamp indexes
От | Mitch Vincent |
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Тема | Re: Timestamp indexes |
Дата | |
Msg-id | 004901bff33a$bd41ebd0$4100000a@doot обсуждение исходный текст |
Ответ на | Timestamp indexes ("Mitch Vincent" <mitch@venux.net>) |
Ответы |
Re: Timestamp indexes
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Список | pgsql-sql |
With enable_seqscan off (Same query) Sort (cost=9282.89..9282.89 rows=4880 width=611) -> Index Scan using applicants_created, applicants_resubmitted on applicants a (cost=0.00..8983.92 rows=4880 width=611) ...and.. ! system usage stats: ! 7.541906 elapsed 5.368217 user 2.062897 system sec ! [5.391668 user 2.070713 sys total] ! 1/543 [2/543] filesystem blocks in/out ! 0/9372 [0/9585] page faults/reclaims, 0 [0] swaps ! 0 [0] signals rcvd, 0/3 [4/7] messages rcvd/sent ! 7/101 [12/107] voluntary/involuntary context switches ! postgres usage stats: ! Shared blocks: 0 read, 0 written, buffer hit rate = 100.00% ! Local blocks: 0 read, 0 written, buffer hit rate = 0.00% ! Direct blocks: 0 read, 0 written CommitTransactionCommand Looks like that index scan is very unattractive... I'll look for some other ways to speed up the query a bit.. Thanks! -Mitch ----- Original Message ----- From: "Tom Lane" <tgl@sss.pgh.pa.us> To: "Mitch Vincent" <mitch@venux.net> Cc: <pgsql-sql@postgresql.org> Sent: Friday, July 21, 2000 1:26 PM Subject: Re: [SQL] Timestamp indexes > "Mitch Vincent" <mitch@venux.net> writes: > > select * from applicants as a where (a.created::date > '05-01-2000' or > > a.resubmitted::date > '05-01-2000') order by (case when a.resubmitted > > > a.created then a.resubmitted else a.created end) desc limit 10 offset 0 > > > There is one of the queries.. I just remembered that the order by was added > > since last time I checked it's PLAN (in the 6.5.X days) -- could that be the > > problem? > > Probably. With the ORDER BY in there, the LIMIT no longer applies > directly to the scan (since a separate sort step is going to be > necessary). Now it's looking at a lot more data to be fetched by > the scan, not just 10 records, so the indexscan becomes less attractive. > > Might be interesting to compare the estimated and actual runtimes > between this query and what you get with "set enable_seqscan to off;" > > regards, tom lane >
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