| From: | Вадим Акбашев <ufaowl(at)gmail(dot)com> |
|---|---|
| To: | Pg Bugs <pgsql-bugs(at)postgresql(dot)org> |
| Subject: | Strange influence of default_statistics_target |
| Date: | 2017-01-18 07:54:43 |
| Message-ID: | CALoKji-qHPvXAL7omEoB0n2g5WudFDmqXf3tsMBUwYdtiiQRVA@mail.gmail.com |
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| Thread: | |
| Lists: | pgsql-bugs |
Hello!
I have encountered a problem with querry plan building:
I'd set default_statistics_target=700, run analyze. Postgres optimize had
chosen plan with hash_join and it took ~1 min for qerry to complete.
Then i set default_statistics_target=500 and the plan was significantly
changed and was using merge_join instead, complition time reduced in
hundreds times, cost reduced drastically.
Now i can't understand why more precise statistics leads to less optimized
plan and what is the right way to use default_statistics_target parameter?
I attach both good and bad querry plans and the querry itself
| Attachment | Content-Type | Size |
|---|---|---|
| dst500.txt | text/plain | 5.3 KB |
| dst700.txt | text/plain | 5.8 KB |
| querry.sql | application/sql | 4.1 KB |
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