Skip site navigation (1) Skip section navigation (2)

Re: cheaper snapshots

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: cheaper snapshots
Date: 2011-07-29 00:15:06
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Thu, Jul 28, 2011 at 8:12 PM, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> wrote:
> On Fri, Jul 29, 2011 at 2:20 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> Well, again, there are three levels:
>> (A) synchronous_commit=off.  No waiting!
>> (B) synchronous_commit=local transactions, and synchronous_commit=on
>> transactions when sync rep is not in use.  Wait for xlog flush.
>> (C) synchronous_commit=on transactions when sync rep IS in use.  Wait
>> for xlog flush and replication.
> ...
>> So basically, you can't be more asynchronous than the guy in front of
>> you.
> (A) still gives a guarantee - transactions that begin after the commit
> returns see
> the commited transaction. A weaker variant would say that if the commit
> returns, and the server doesn't crash in the meantime, the commit would at
> some point become visible. Maybe even that transactions that begin after the
> commit returns become visible after that commit.

Yeah, you could do that.  But that's such a weak guarantee that I'm
not sure it has much practical utility.

Robert Haas
The Enterprise PostgreSQL Company

In response to

pgsql-hackers by date

Next:From: Noah MischDate: 2011-07-29 03:05:15
Subject: Re: sinval synchronization considered harmful
Previous:From: Robert HaasDate: 2011-07-29 00:14:53
Subject: Re: cheaper snapshots

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group