On Tue, Oct 17, 2017 at 2:29 AM, Thomas Munro
<thomas.mu...@enterprisedb.com> wrote:
> Vik Fearing asked off-list why hash joins appear to read slightly more
> temporary data than they write.  The reason is that we notch up a
> phantom block read when we hit the end of each file.  Harmless but it
> looks a bit weird and it's easily fixed.
> Unpatched, a 16 batch hash join reports that we read 30 more blocks
> than we wrote (2 per batch after the first, as expected):
>    Buffers: shared hit=434 read=16234, temp read=5532 written=5502
> With the attached patch:
>    Buffers: shared hit=547 read=16121, temp read=5502 written=5502

Committed.  Arguably we ought to back-patch this, but it's minor so I didn't.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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