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Re: lazy vxid locks, v3

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: lazy vxid locks, v3
Date: 2011-08-01 16:12:41
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Lists: pgsql-hackers
On Mon, Aug 1, 2011 at 11:21 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Mon, 2011-08-01 at 08:12 -0400, Robert Haas wrote:
>> > Is the "&& LocalTransactionIdIsValid(lxid)" a guard against calling
>> > VirtualXactLockTableCleanup twice? Can that happen? Or is it just
>> > defensive coding to avoid making an additional assumption?
>> lxid there is just a local variable storing the value that we
>> extracted from fpLocalTransactionId while holding the lock.  I named
>> it that way just as a mnemonic for the type of value that it was, not
>> intending to imply that it was copied from MyProc->lxid.
> I know, this is the other purpose of fpLocalTransactionId that I was
> talking about. Is it just a guard against calling
> VirtualXactLockTableCleanup twice?

I guess you could look at that way.  It just seemed like the obvious
way to write the code: we do LockRefindAndRelease() only if we have a
fast-path lock that someone else has pushed into the main table.

Robert Haas
The Enterprise PostgreSQL Company

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