On 30/04/15 00:44, Tom Lane wrote:
Robert Haas <robertmh...@gmail.com> writes:
On Mon, Apr 20, 2015 at 9:03 AM, Tomas Vondra
<tomas.von...@2ndquadrant.com> wrote:
Sure, it's not an ultimate solution, but it might help a bit. I do have
other ideas how to optimize this, but in the planner every milisecond
counts. Looking at 'perf top' and seeing pglz_decompress() in top 3.
I suggested years ago that we should not compress data in
pg_statistic. Tom shot that down, but I don't understand why. It
seems to me that when we know data is extremely frequently accessed,
storing it uncompressed makes sense.
I've not been following this thread, but I do not think your argument here
holds any water. pg_statistic entries are generally fetched via the
syscaches, and we fixed things years ago so that toasted tuple entries
are detoasted before insertion in syscache. So I don't believe that
preventing on-disk compression would make for any significant improvement,
at least not after the first reference within a session.
AFAICS the syscache tuples are detoasted but not decompressed before
insertion to syscache (catcache calls toast_flatten_tuple which doesn't
do decompression) so the pglz_decompress is still called every time.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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