Re: [HACKERS] Dead code in _bt_split?

Your patch has been added to the PostgreSQL unapplied patches list at:

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It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.

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Heikki Linnakangas wrote:
> Tom Lane wrote:
> > While testing it I realized that there seems to be a nearby bug in
> > _bt_findsplitloc: it fails to consider the possibility of moving all the
> > extant items to the left side. It will always return a firstright <=
> > maxoff. ISTM this would mean that it could choose a bad split if the
> > incoming item goes at the end and both it and the last extant item are
> > large: in this case they should be split apart, but they won't be.
> >
> > Heikki, do you feel like looking at that, or shall I?
>
> I refactored findsplitloc and checksplitloc so that the division of
> labor is more clear IMO. I pushed all the space calculation inside the
> loop to checksplitloc.
>
> I also fixed the off by 4 in free space calculation caused by
> PageGetFreeSpace subtracting sizeof(ItemIdData), even though it was
> harmless, because it was distracting and I felt it might come back to
> bite us in the future if we change the page layout or alignments.
> There's now a new function PageGetExactFreeSpace that doesn't do the
> subtraction.
>
> findsplitloc now tries the "just the new item to right page" split as
> well. If people don't like the refactoring, I can write a patch to just
> add that.
>
> Some of the long variable names look ugly. camelCase or underscores
> between words would be more readable, but I retained the old style for
> the sake of consistency.
>
> --
> Heikki Linnakangas
> EnterpriseDB http://www.enterprisedb.com

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

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