On 07-Nov-2012, at 15:46, Amit Kapila <amit.kap...@huawei.com> wrote:
>> From: pgsql-hackers-ow...@postgresql.org [mailto:pgsql-hackers- >> ow...@postgresql.org] On Behalf Of Merlin Moncure >> Sent: Wednesday, November 07, 2012 5:26 AM >> To: PostgreSQL-development >> Cc: Atri Sharma >> Subject: [HACKERS] WIP patch for hint bit i/o mitigation >> >> Following the sig is a first cut at a patch (written by Atri) that >> attempts to mitigate hint bit i/o penalty when many pages worth of >> tuples are sequentially written out with the same transaction id. >> There have been other attempts to deal with this problem that fit >> niche cases (especially those that create the table in the same >> transaction as the one inserting) that work but don't really solve the >> problem generally. >> >> I previously attacked this problem ([1], [2]) and came up with a patch >> that cached hint bits inside tqual.c. The patch was pulled for a few >> reasons: >> >> 1) a lot of complexity without proper justification >> 2) sketchy cache replacement algorithm >> 3) I manged to misspell 'committed' just about everywhere >> 4) invalidation? >> >> Issues 1-3 could have been worked out but #4 was making me think the >> problem was a nonstarter, or at least, 'too much too soon'. The tuple >> visibility routines are in a very tight code path and having to deal >> with various things in the backend that could cause the xid to become >> stale were making me nervous. A smaller, simpler patch might be the >> ticket. > > About invalidation, I think the cached xid can become invalid due to xid > wraparound. > So for that one way could be to invalidate it through Vacuum. > > Though I am not sure what all other things can make cached id as invalid, > but I think once we > can think what other ways can make cached id invalid, then we can see if > there is a solution to address > them. > > > With Regards, > Amit Kapila. > > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers As we are now dealing with only the last xid(please refer to the details of the patch attached), the invalidation issues are not significant any more. Regards, Atri -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
