Re: [GENERAL] Joining 16 tables seems slow
| От | Pavel Stehule |
|---|---|
| Тема | Re: [GENERAL] Joining 16 tables seems slow |
| Дата | |
| Msg-id | CAFj8pRDirLEjKjgEjv-0iCqxyJwtjOX8CCEaWaiyOR4S8BSx3w@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: [GENERAL] Joining 16 tables seems slow (Tom Lane <tgl@sss.pgh.pa.us>) |
| Список | pgsql-general |
2017-09-12 14:01 GMT+02:00 Tom Lane <tgl@sss.pgh.pa.us>:
"Frank Millman" <frank@chagford.com> writes:
> Pavel Stehule wrote:
>> 2017-09-12 8:45 GMT+02:00 Frank Millman <frank@chagford.com>:
>>> I am experimenting with optimising a SQL statement. One version uses 4 LEFT JOIN’s and a 5-way CASE statement in the body. The second moves the filtering into the JOIN section, and I end up with 16 LEFT JOIN’s and no CASE statements.
>> you can experimentally try increase FROM_COLLAPSE_LIMIT to some higher number 14 maybe 16
> I tried increasing FROM_COLLAPSE_LIMIT, but it made no difference.
For this you need to increase join_collapse_limit, not
from_collapse_limit. (Usually, though, there's little reason not to keep
them the same.)
sure - my mistake - I though it.
Thank you
Pavel
regards, tom lane
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