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

help / color / mirror / Atom feed
From: Joshua D. Drake <jd@commandprompt.com>
To: Robert Haas <robertmhaas@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Greg Stark <stark@mit.edu>
Cc: Andres Freund <andres@2ndquadrant.com>
Cc: Rajeev rastogi <rajeev.rastogi@huawei.com>
Cc: Markus Wanner <markus@bluegap.ch>
Cc: Ants Aasma <ants@cybertec.at>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: obartunov <obartunov@postgrespro.ru>
Cc: Teodor Sigaev <teodor@postgrespro.ru>
Subject: Re: Proposal for CSN based snapshots
Date: Wed, 10 Aug 2016 08:54:48 -0700
Message-ID: <3406288c-9989-5c95-4445-5443b7a7b66f@commandprompt.com> (raw)
In-Reply-To: <CA+TgmoaZizCOkfJ4uuepBqJ0PSrBYnCDEaUk8xoK3SEbnSMGZQ@mail.gmail.com>
References: <51B6C97B.1070000@bluegap.ch>
	<CAM-w4HMG-YeTfWc3r_excej3Kd04q4zDDXR0hxShVbij211ABA@mail.gmail.com>
	<539AD153.9000004@vmware.com>
	<1409043789.2335.330.camel@jeff-desktop>
	<53FC6545.7000501@vmware.com>
	<1409116988.2335.463.camel@jeff-desktop>
	<53FD7D65.9040602@vmware.com>
	<53FD7DCC.5020005@vmware.com>
	<CAPpHfdsCUb4qBUHzfqNsUYALC_LEpHD9qB-ozvS_8esv1edCTw@mail.gmail.com>
	<CANP8+jLAe3Smtq3FF49DMvuxtfoRQcCPQn28GEKuwAb2J41XCA@mail.gmail.com>
	<CA+Tgmob1DmDsvc7iyd0SY5j4SFdesDwoef36bxG1pE_s1JQXOQ@mail.gmail.com>
	<CANP8+jLyhL92eJi7RVX_yvbKjxm9=OBKcmNnodaYmeE+o2i1+Q@mail.gmail.com>
	<CAPpHfdv7BMwGv=OfUg3S-jGVFKqHi79pR_ZK1Wsk-13oZ+cy5g@mail.gmail.com>
	<69041c5a-ec60-3c54-49d0-5df071b27f52@iki.fi>
	<a7e33ad4-cf1e-2e7c-6752-de91302292dc@iki.fi>
	<79213506-4c9c-7e7a-44c6-ae94484c1159@iki.fi>
	<6906.1470840684@sss.pgh.pa.us>
	<8c150c9d-6ba2-69fd-e908-ed2fc2775c05@iki.fi>
	<CA+TgmoaZizCOkfJ4uuepBqJ0PSrBYnCDEaUk8xoK3SEbnSMGZQ@mail.gmail.com>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>

On 08/10/2016 08:28 AM, Robert Haas wrote:
> On Wed, Aug 10, 2016 at 11:09 AM, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>>> Still, having to invent CSNs seems like a huge loss for this design.
>>> Personally I'd give up async commit first.  If we had only sync commit,
>>> the rule could be "xact LSN less than snapshot threshold and less than
>>> WAL flush position", and we'd not need CSNs.  I know some people like
>>> async commit, but it's there because it was easy and cheap in our old
>>> design, not because it's the world's greatest feature and worth giving
>>> up performance for.
>>
>> I don't think that's a very popular opinion (I disagree, for one).
>> Asynchronous commits are a huge performance boost for some applications. The
>> alternative is fsync=off, and I don't want to see more people doing that.
>> SSDs have made the penalty of an fsync much smaller, but it's still there.
>
> Uh, yeah.  Asynchronous commit can be 100 times faster on some
> realistic workloads.  If we remove it, many people will have to decide
> between running with fsync=off and abandoning PostgreSQL altogether.
> That doesn't strike me as a remotely possible line of attack.

+1 for Robert here, removing async commit is a non-starter. It is 
PostgreSQL performance 101 that you disable synchronous commit unless 
you have a specific data/business requirement that needs it. 
Specifically because of how much faster Pg is with async commit.

Sincerely,

jD


>


-- 
Command Prompt, Inc.                  http://the.postgres.company/
                         +1-503-667-4564
PostgreSQL Centered full stack support, consulting and development.
Everyone appreciates your honesty, until you are honest with them.
Unless otherwise stated, opinions are my own.


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers



view thread (113+ messages)  latest in thread

Message-ID: <3406288c-9989-5c95-4445-5443b7a7b66f@commandprompt.com>
Permalink:  ../3406288c-9989-5c95-4445-5443b7a7b66f@commandprompt.com/
Also on:    postgresql.org/message-id/3406288c-9989-5c95-4445-5443b7a7b66f@commandprompt.com

 · 

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-hackers@postgresql.org
  Cc: jd@commandprompt.com, robertmhaas@gmail.com, hlinnaka@iki.fi, tgl@sss.pgh.pa.us, a.korotkov@postgrespro.ru, simon@2ndquadrant.com, dilipbalaut@gmail.com, pgsql@j-davis.com, alvherre@2ndquadrant.com, stark@mit.edu, andres@2ndquadrant.com, rajeev.rastogi@huawei.com, markus@bluegap.ch, ants@cybertec.at, bruce@momjian.us, obartunov@postgrespro.ru, teodor@postgrespro.ru
  Subject: Re: Proposal for CSN based snapshots
  In-Reply-To: <3406288c-9989-5c95-4445-5443b7a7b66f@commandprompt.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