Simon Riggs <si...@2ndquadrant.com> writes: > On Wed, Nov 23, 2011 at 5:01 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> Simon Riggs <si...@2ndquadrant.com> writes: >>> Normal catalog access does not use HOT and never has.
>> You are mistaken. > Normal catalog access against shared catalogs via heap_scan does not > use HOT cleanup, because it uses SnapshotNow. Not sure what you are basing these statements on. Normal catalog access typically goes through indexam.c, which AFAICS will call heap_page_prune_opt on every heap page it visits, quite independently of what snapshot is used. There are no cases I know of where the system prefers heapscans on catalogs, except possibly pg_am which is known to be small. > However, since we're talking about these tables only > ... > then I think it's fair to say that they are seldom updated/deleted and > so the effect of HOT cleanup is not important for those tables. I agree with Alvaro that pg_shdepend is probably a bit too volatile to make such an assumption safe. > The real question is do we favour HOT cleanup on those small 8 tables, > or do we favour HOT cleanup of every other table? No, the real question is why not think a little harder and see if we can come up with a solution that doesn't involve making some cases worse to make others better. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers