|From:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|To:||"Robert Haas" <robertmhaas(at)gmail(dot)com>|
|Cc:||"Gregory Stark" <stark(at)enterprisedb(dot)com>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Postgres <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: posix_fadvise v22|
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"Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
> OK, here's an update of Greg's patch with the runtime configure test
> ripped out, some minor documentation tweaks, and a few unnecessary
> whitespace diff hunks quashed. I think this is about ready for
> committer review.
I've started to look through this, and the only part I seriously don't
like is the nbtsearch.c changes. I've got three complaints about that:
* Doing it inside the index AMs is wrong, or at the very least forces
us to do it over for each index AM (which the patch fails to do).
* As coded, it generates prefetch bursts that are much too large and too
widely spaced to be effective, not to mention that they entirely
ignore the effective_io_concurrency control knob as well as the order
in which the pages will actually be needed. I wonder now whether
Robert's inability to see any benefit came because he was testing
indexscans and not bitmap scans.
* It's only accidental that it's not kicking in during a bitmap
indexscan and bollixing up the much-more-carefully-written
nodeBitmapHeapscan prefetch logic.
What I intend to do over the next day or so is commit the prefetch
infrastructure and the bitmap scan prefetch logic, but I'm bouncing the
indexscan part back for rework. I think that it should be implemented
in or near index_getnext() and pay attention to
regards, tom lane
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