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Is the attribute options cache actually worth anything?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Is the attribute options cache actually worth anything?
Date: 2011-03-01 18:15:34
Message-ID: 22987.1299003334@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
So while poking at a recent example from Marc Cousin (hundreds of tables
each with 1000 attributes) I observed that a simple ANALYZE would bloat
the backend process to the tune of several hundred megabytes.  I think
there is a leak in CacheMemoryContext, but haven't tracked it down yet.
But I also noticed that tens of megabytes were disappearing into "Attopt
cache", and after reading the code to see what the heck that was, I am
wondering what the justification for having it is at all.  In the
presumably normal case where the attribute hasn't got options, all it's
saving us is a syscache access, which is probably not noticeably more
expensive than the hash lookup.  In the case where there is an option,
it's saving us an attribute_reloptions() call, but it's not apparent
to me that that's so expensive as to justify putting a cache in front
of it, especially not if we're going to do a palloc cycle anyway.

Did anybody do any performance measurements to demonstrate that this
code has a reason to live?  Because if I don't see some, I'm going
to rip it out.

			regards, tom lane

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