Re: advancing snapshot's xmin - Mailing list pgsql-hackers

From Neil Conway
Subject Re: advancing snapshot's xmin
Date
Msg-id 1206484813.32670.7.camel@goldbach
Whole thread Raw
In response to advancing snapshot's xmin  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: advancing snapshot's xmin  ("Heikki Linnakangas" <heikki@enterprisedb.com>)
List pgsql-hackers
On Tue, 2008-03-25 at 17:26 -0300, Alvaro Herrera wrote:
> There is one hole here: contention on ProcArrayLock.  Basically, for
> simple transactions we will need to update MyProc after every command.

If we're just updating MyProc->xmin, we only need to acquire
ProcArrayLock in shared mode, right?

> Another idea is to throttle the updating of Xmin so it only happens once
> in a while, but it's difficult to find a useful criterion and avoid
> falling into the trap that we just neglected to update it before a large
> command.

Using LWLockConditionalAcquire() might help also.

-Neil




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