Re: SSI heap_insert and page-level predicate locks

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: "Dan Ports" <drkp(at)csail(dot)mit(dot)edu>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: SSI heap_insert and page-level predicate locks
Date: 2011-06-08 22:29:13
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> heap_insert() calls CheckForSerializableConflictIn(), which checks if

> there is a predicate lock on the whole relation, or on the page we're

> inserting to. It does not check for tuple-level locks, because there

> can't be any locks on a tuple that didn't exist before.
> AFAICS, the check for page lock is actually unnecessary. A page-level

> lock on a heap only occurs when tuple-level locks are promoted. It is

> just a coarser-grain representation of holding locks on all tuples on

> the page, *that exist already*. It is not a "gap" lock like the index

> locks are, it doesn't need to conflict with inserting new tuples on
> page. In fact, if heap_insert chose to insert the tuple on some other

> heap page, there would have been no conflict.

Absolutely correct. Patch attached.


Attachment Content-Type Size
ssi-heap-insert-fix-1.patch text/plain 1.1 KB

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