Horton

Re: foreign key locks, 2nd attempt

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Simon Riggs <simon@2ndquadrant.com>, Noah Misch <noah@leadboat.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2012-02-23T15:28:20Z
Lists: pgsql-hackers

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  1. Try to avoid running with a full fsync request queue.

Alvaro Herrera <alvherre@commandprompt.com> writes:
> Sure.  The problem is that we are allowing updated rows to be locked (and
> locked rows to be updated).  This means that we need to store extended
> Xmax information in tuples that goes beyond mere locks, which is what we
> were doing previously -- they may now have locks and updates simultaneously.

> (In the previous code, a multixact never meant an update, it always
> signified only shared locks.  After a crash, all backends that could
> have been holding locks must necessarily be gone, so the multixact info
> is not interesting and can be treated like the tuple is simply live.)

Ugh.  I had not been paying attention to what you were doing in this
patch, and now that I read this I wish I had objected earlier.  This
seems like a horrid mess that's going to be unsustainable both from a
complexity and a performance standpoint.  The only reason multixacts
were tolerable at all was that they had only one semantics.  Changing
it so that maybe a multixact represents an actual updater and maybe
it doesn't is not sane.

			regards, tom lane