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Re: Snapshot synchronization, again...

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Joachim Wieland <joe(at)mcknight(dot)de>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Snapshot synchronization, again...
Date: 2011-02-28 17:59:56
Message-ID: 26171.1298915996@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Sun, Feb 27, 2011 at 8:33 PM, Joachim Wieland <joe(at)mcknight(dot)de> wrote:
>> Remember that it's not only about saving shared memory, it's also
>> about making sure that the snapshot reflects a state of the database
>> that has actually existed at some point in the past.

> But you can do all of this with files too, can't you?  Just remove or
> truncate the file when the snapshot is no longer valid.

Yeah.  I think adopting a solution similar to 2PC state files is a very
reasonable way to go here.  This isn't likely to be a high-usage or
performance-critical feature, so it's not essential to keep the
information in shared memory for performance reasons.

			regards, tom lane

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