Thread: Is the attribute options cache actually worth anything?
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
On Tue, Mar 1, 2011 at 1:15 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > 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. No, I have to admit I didn't do that. Might be worth doing some before you commit the rip-out, though. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
Tom Lane wrote: > 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. Did we decide to keep the cache in attoptcache.c? Is this a TODO? -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +
Bruce Momjian <bruce@momjian.us> writes:
> Tom Lane wrote:
>> 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.
> Did we decide to keep the cache in attoptcache.c? Is this a TODO?
It's still a TODO, I think --- the code's still there, and nobody's done
any performance measurements either way.
regards, tom lane