Re: Out of Memory errors are frustrating as heck!

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От Tom Lane
Тема Re: Out of Memory errors are frustrating as heck!
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Msg-id 14066.1555793163@sss.pgh.pa.us
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Ответ на Re: Out of Memory errors are frustrating as heck!  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
Ответы Re: Out of Memory errors are frustrating as heck!  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
Re: Out of Memory errors are frustrating as heck!  (Justin Pryzby <pryzby@telsasoft.com>)
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Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> I think it's really a matter of underestimate, which convinces the planner
> to hash the larger table. In this case, the table is 42GB, so it's
> possible it actually works as expected. With work_mem = 4MB I've seen 32k
> batches, and that's not that far off, I'd day. Maybe there are more common
> values, but it does not seem like a very contrived data set.

Maybe we just need to account for the per-batch buffers while estimating
the amount of memory used during planning.  That would force this case
into a mergejoin instead, given that work_mem is set so small.

            regards, tom lane



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