From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org, Hiroyuki Yamada <yamada@kokolink.net>
Subject: Re: Synchronization primitives (Was: Re: An example of bugs for Hot Standby)
Date: Wed, 20 Jan 2010 20:49:03 +0200
Message-ID: <4B57501F.8030804@enterprisedb.com> (raw)
In-Reply-To: <16135.1264011365@sss.pgh.pa.us>
References: <200912151111.AA00168@silver.kokolink.net>
<201001201740.22069.andres@anarazel.de>
<14578.1264006776@sss.pgh.pa.us>
<201001201841.15760.andres@anarazel.de>
<4B5744C1.40806@enterprisedb.com>
<16135.1264011365@sss.pgh.pa.us>
Tom Lane wrote:
> Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
>> Streaming Replication introduces a few places with a polling pattern
>> like this (in pseudocode):
>
>> while()
>> {
>> /* Check if variable in shared has advanced beoynd X */
>> SpinLockAcquire()
>> localvar = sharedvar;
>> SpinLockRelease()
>> if (localvar > X)
>> break;
>
>> /* Not yet. Sleep
>> pg_usleep(100);
>> }
>
> I trust there's a CHECK_FOR_INTERRUPTS in there ...
>
>> It would be nice to have a new synchronization primitive for that.
>
> Maybe. The lock, the variable, the comparison operation, and the sleep
> time all seem rather specific to each application. Not sure that it'd
> really buy much to try to turn it into a generic subroutine.
My point is that we should replace such polling loops with something
non-polling, using wait/signal or semaphores or something. That gets
quite a bit more complex. You'd probably still have the loop, but
instead of pg_usleep() you'd call some new primitive function that waits
until the shared variable changes.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: heikki.linnakangas@enterprisedb.com, tgl@sss.pgh.pa.us, andres@anarazel.de, simon@2ndquadrant.com, yamada@kokolink.net
Subject: Re: Synchronization primitives (Was: Re: An example of bugs for Hot Standby)
In-Reply-To: <4B57501F.8030804@enterprisedb.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox