Re: [PERFORM] Very slow (2 tuples/second) sequential scan after bulk insert; speed returns to ~500 tuples/second after commit

This has been applied by Tom.

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Heikki Linnakangas wrote:
> Tom Lane wrote:
> > "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:
> >> Elsewhere in our codebase where we use arrays that are enlarged as
> >> needed, we keep track of the "allocated" size and the "used" size of the
> >> array separately, and only call repalloc when the array fills up, and
> >> repalloc a larger than necessary array when it does. I chose to just
> >> call repalloc every time instead, as repalloc is smart enough to fall
> >> out quickly if the chunk the allocation was made in is already larger
> >> than the new size. There might be some gain avoiding the repeated
> >> repalloc calls, but I doubt it's worth the code complexity, and calling
> >> repalloc with a larger than necessary size can actually force it to
> >> unnecessarily allocate a new, larger chunk instead of reusing the old
> >> one. Thoughts on that?
> >
> > Seems like a pretty bad idea to me, as the behavior you're counting on
> > only applies to chunks up to 8K or thereabouts.
>
> Oh, you're right. Though I'm sure libc realloc has all kinds of smarts
> as well, it does seem better to not rely too much on that.
>
> > In a situation where
> > you are subcommitting lots of XIDs one at a time, this is likely to have
> > quite awful behavior (or at least, you're at the mercy of the local
> > malloc library as to how bad it is). I'd go with the same
> > double-it-each-time-needed approach we use elsewhere.
>
> Yep, patch attached. I also changed xactGetCommittedChildren to return
> the original array instead of copying it, as Alvaro suggested.
>
> --
> Heikki Linnakangas
> EnterpriseDB http://www.enterprisedb.com

>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com

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