pg.ddx.io  pgsql-performance@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Daniel Farina <daniel@heroku.com>
Cc: Craig Ringer <ringerc@ringerc.id.au>
Cc: Harold A. Giménez <harold.gimenez@gmail.com>
Subject: Re: [PERFORM] DELETE vs TRUNCATE explanation
Date: Mon, 16 Jul 2012 12:36:31 -0400
Message-ID: <11952.1342456591@sss.pgh.pa.us> (raw)
In-Reply-To: <CA+Tgmoa4ta60Y-rZpEPDRCQKJV8-Uqe0P610Jgj2q7e+fondig@mail.gmail.com>
References: <4FFCCAC4.4030503@ringerc.id.au>
	<CAAZKuFZ9tYeC1K5ZayZgztm3re_7ytbsEYFa0wwXirB6Hfm+EQ@mail.gmail.com>
	<23853.1342015548@sss.pgh.pa.us>
	<CAAZKuFYsK+ZQuC=zf0xE=M-LNa02tB7RBy3CHEUyq7LWCkK6jQ@mail.gmail.com>
	<CAMkU=1ydaypgAeZxyaMc=KhJJw5riGMBiLpvSqOO42=qArRZmQ@mail.gmail.com>
	<32078D4B40DD40ECB739D0ECD7D95996@gmail.com>
	<CAMkU=1zJK6WiS9-6eO8rNmRpKSSB4=uw2mTsD=k64mNh__=Dcg@mail.gmail.com>
	<CAMkU=1w7vLA63hf-+Uc_j61CvOdKixsOHph9d0H-aLNBYgfX=w@mail.gmail.com>
	<CAMkU=1yLXvODRZZ_=fgrEeJfk2tvZPTTD-8n8BwrAhNz_WBT0A@mail.gmail.com>
	<19949.1342376967@sss.pgh.pa.us>
	<CA+TgmoaTf=zjP37-oG7fr1VbGfuvHSfpajgLZ65EeSJX2mmquA@mail.gmail.com>
	<9603.1342454919@sss.pgh.pa.us>
	<CA+Tgmoa4ta60Y-rZpEPDRCQKJV8-Uqe0P610Jgj2q7e+fondig@mail.gmail.com>

Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Jul 16, 2012 at 12:08 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Uh, that's exactly what's under discussion.  Not sending useless fsync
>> requests when fsync is off is just one part of it; a part that happens
>> to be quite useful for some test scenarios, even if not so much for
>> production.  (IIRC, the original complainant in this thread was running
>> fsync off.)

> My point is that if sending fsync requests is cheap enough, then not
> sending them won't save anything meaningful.

Well, that argument is exactly why the code is designed the way it is...
but we are now finding out that sending useless fsync requests isn't as
cheap as all that.

The larger point here, in any case, is that I don't believe anyone wants
to expend a good deal of skull sweat and possibly performance on
ensuring that transitioning from fsync off to fsync on in an active
database is a reliable operation.  It does not seem like something we
are ever going to recommend, and we have surely got nine hundred ninety
nine other things that are more useful to spend development time on.

			regards, tom lane



view thread (46+ messages)  latest in thread

Message-ID: <11952.1342456591@sss.pgh.pa.us>
Permalink:  ../11952.1342456591@sss.pgh.pa.us/
Also on:    postgresql.org/message-id/11952.1342456591@sss.pgh.pa.us

 · 

reply
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-performance@postgresql.org
  Cc: tgl@sss.pgh.pa.us, robertmhaas@gmail.com, jeff.janes@gmail.com, pgsql-hackers@postgresql.org, daniel@heroku.com, ringerc@ringerc.id.au, harold.gimenez@gmail.com
  Subject: Re: [PERFORM] DELETE vs TRUNCATE explanation
  In-Reply-To: <11952.1342456591@sss.pgh.pa.us>

* 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