| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: XLogInsert scaling, revisited |
| Date: | 2013-07-02 17:15:23 |
| Message-ID: | 20130702171523.GA27409@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2013-07-02 19:48:40 +0300, Heikki Linnakangas wrote:
> >If so, why isn't it sufficient to
> >initialize it in ReserveXLogInsertLocation?
>
> It would be, but then ReserveXLogInsertLocation would need to hold the
> slot's spinlock at the same time with insertpos_lck, so that it could
> atomically read the current CurrBytePos value and copy it to
> xlogInsertingAt. It's important to keep ReserveXLogInsertLocation() as
> lightweight as possible, to maximize concurrency.
If you make it so that you always acquire the slot's spinlock first and
insertpos_lck after, the scalability shouldn't be any different from
now? Both the duration during which insertpos_lck is held and the
overall amount of atomic ops should be the same?
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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