Re: dsa_allocate() faliure

On Sun, Feb 10, 2019 at 2:37 AM Thomas Munro
<thomas.munro@enterprisedb.com> wrote:
> ... but why would it do that?  I can reproduce cases where (for
> example) FreePageManagerPutInternal() returns 179, and then
> FreePageManagerLargestContiguous() returns 179, but then after
> FreePageBtreeCleanup() it returns 178.  At that point FreePageDump()
> says:
>
>     btree depth 1:
>       77@0 l: 27(1) 78(178)
>     freelists:
>       1: 27
>       129: 78(178)
>
> But at first glance it shouldn't be allocating pages, because it just
> does consolidation to try to convert to singleton format, and then it
> does recycle list cleanup using soft=true so that no allocation of
> btree pages should occur.

I think I see what's happening.  At the moment the problem occurs,
there is no btree - there is only a singleton range.  So
FreePageManagerInternal() takes the fpm->btree_depth == 0 branch and
then ends up in the section with the comment  /* Not contiguous; we
need to initialize the btree. */.  And that section, sadly, does not
respect the 'soft' flag, so kaboom.  Something like the attached might
fix it.

Boy, I love FreePageManagerDump!

-- 
Robert Haas
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