Re: FOR KEY LOCK foreign keys

Hackers,

This is an updated version of the patch I introduced here:

http://archives.postgresql.org/message-id/1294953201-sup-2099@alvh.no-ip.org

Mainly, this patch addresses the numerous comments by Noah Misch here:
http://archives.postgresql.org/message-id/20110211071322.GB26971@tornado.leadboat.com
My thanks to Noah for the very exhaustive review and ideas.

I also removed the bit about copying the ComboCid to the new version of
the tuple during an update.  I think that must have been the result of
very fuzzy thinking; I cannot find any reasoning that leads to it being
necessary, or even correct.

I also included Marti Raudsepp's patch to consider only indexes usable
in foreign keys.

One thing I have not addressed is Noah's idea about creating a new lock
mode, KEY UPDATE, that would let us solve the initial problem that this
patch set to resolve in the first place.  I am not clear on exactly how
that is to be implemented, because currently heap_update and heap_delete
do not grab any kind of lock but instead do their own ad-hoc waiting.  I
think that might need to be reshuffled a bit, to which I haven't gotten
yet, and is a radical enough idea that I would like it to be discussed
by the hackers community at large before setting sail on developing it.
In the meantime, this patch does improve the current situation quite a
lot.

--
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
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