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

help / color / mirror / Atom feed
From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Robert Haas <robertmhaas@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] WAL logging problem in 9.4.3?
Date: Wed, 18 Jul 2018 17:58:16 +0300
Message-ID: <c7d2ca8a-d376-f19b-e95e-b879efc3b860@iki.fi> (raw)
In-Reply-To: <CA+Tgmob_aF_rQmczNDUXZz2z+MksFmCyP7-3KvuauuWoS9400g@mail.gmail.com>
References: <20180704045912.GG1672@paquier.xyz>
	<df32e286-ae2b-f45a-8f2e-4fa02684300b@iki.fi>
	<20180711033241.GQ1661@paquier.xyz>
	<aac8e19b-9159-e473-77be-53f80b658190@2ndQuadrant.com>
	<08b11907-d0b2-c396-2978-ba5aac1972df@iki.fi>
	<CA+TgmoZGn7MmMGRu4NkfxyXKSCzmvq1JvqsWm=hN=GJDMTfTKg@mail.gmail.com>
	<026AD6A1-3396-47F4-B87E-77E3F139D166@iki.fi>
	<20180717000129.GA3388@paquier.xyz>
	<3c1cf991-8846-9a6f-c669-e21f8ea9a6a4@2ndQuadrant.com>
	<CA+TgmoZU9nBd6m3NQohzjpdvBNtw+6UGoz+uqoaawkXy76gYSg@mail.gmail.com>
	<20180718130622.GI8565@paquier.xyz>
	<CA+Tgmob_aF_rQmczNDUXZz2z+MksFmCyP7-3KvuauuWoS9400g@mail.gmail.com>

On 18/07/18 16:29, Robert Haas wrote:
> On Wed, Jul 18, 2018 at 9:06 AM, Michael Paquier <michael@paquier.xyz> wrote:
>>> What's wrong with the approach proposed in
>>> http://postgr.es/m/55AFC302.1060805@iki.fi ?
>>
>> For back-branches that's very invasive so that seems risky to me
>> particularly seeing the low number of complaints on the matter.
> 
> Hmm. I think that if you disable the optimization, you're betting that
> people won't mind losing performance in this case in a maintenance
> release.  If you back-patch Heikki's approach, you're betting that the
> committed version doesn't have any bugs that are worse than the status
> quo.  Personally, I'd rather take the latter bet.  Maybe the patch
> isn't all there yet, but that seems like something we can work
> towards.  If we just give up and disable the optimization, we won't
> know how many people we ticked off or how badly until after we've done
> it.

Yeah. I'm not happy about backpatching a big patch like what I proposed, 
and Kyotaro developed further. But I think it's the least bad option we 
have, the other options discussed seem even worse.

One way to review the patch is to look at what it changes, when 
wal_level is *not* set to minimal, i.e. what risk or overhead does it 
pose to users who are not affected by this bug? It seems pretty safe to me.

The other aspect is, how confident are we that this actually fixes the 
bug, with least impact to users using wal_level='minimal'? I think it's 
the best shot we have so far. All the other proposals either don't fully 
fix the bug, or hurt performance in some legit cases.

I'd suggest that we continue based on the patch that Kyotaro posted at 
https://www.postgresql.org/message-id/20180330.100646.86008470.horiguchi.kyotaro%40lab.ntt.co.jp.

- Heikki




view thread (244+ messages)  latest in thread

Message-ID: <c7d2ca8a-d376-f19b-e95e-b879efc3b860@iki.fi>
Permalink:  ../c7d2ca8a-d376-f19b-e95e-b879efc3b860@iki.fi/
Also on:    postgresql.org/message-id/c7d2ca8a-d376-f19b-e95e-b879efc3b860@iki.fi

 · 

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: hlinnaka@iki.fi, robertmhaas@gmail.com, michael@paquier.xyz, andrew.dunstan@2ndquadrant.com
  Subject: Re: [HACKERS] WAL logging problem in 9.4.3?
  In-Reply-To: <c7d2ca8a-d376-f19b-e95e-b879efc3b860@iki.fi>

* 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