From: Andres Freund <andres@anarazel.de>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Martijn van Oosterhout <kleptog@svana.org>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: WAL logging problem in 9.4.3?
Date: Fri, 3 Jul 2015 19:02:29 +0200
Message-ID: <20150703170229.GJ3291@awork2.anarazel.de> (raw)
In-Reply-To: <20150703164931.GI3291@awork2.anarazel.de>
References: <20150702220524.GA9392@svana.org>
<20150702222102.GG30708@awork2.anarazel.de>
<20150703052048.GA20285@svana.org>
<CAHGQGwEXta1tMF6o-FcDcjMgCF=jnZLj3v3EoePvsEN4aexJnA@mail.gmail.com>
<20150703060137.GB20285@svana.org>
<CAHGQGwFtOMv5h8eKX6zf+9_0UxpcTsyH9xAnyv6KdGH4BonLiw@mail.gmail.com>
<28320.1435935120@sss.pgh.pa.us>
<CAHGQGwGzxAyKLUm+z2n43-ee6u976jLmQAz=pPBVzSueD3CAig@mail.gmail.com>
<20150703164931.GI3291@awork2.anarazel.de>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>
On 2015-07-03 18:49:31 +0200, Andres Freund wrote:
> But the more interesting question is why that's not hhappening
> today. RelationTruncateIndexes() does call the index_build() which
> should end up WAL logging the index creation.
So that's because there's an XLogIsNeeded() preventing it.
Maybe I'm just daft right now (35C outside, 32 inside, so ...), but I'm
right now missing how the whole "skip wal logging if relation has just
been truncated" optimization can ever actually be crashsafe unless we
use a new relfilenode (which we don't!).
Sure, we do an heap_sync() at the the end of the transaction. That's
nice and all. But it doesn't help if we crash and re-start WAL apply
from a checkpoint before the table was created. Because that'll replay
the truncation.
That's much worse than just the indexes - the rows added by a COPY
without WAL logging will also be truncated away, no?
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
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: andres@anarazel.de, masao.fujii@gmail.com, tgl@sss.pgh.pa.us, kleptog@svana.org
Subject: Re: WAL logging problem in 9.4.3?
In-Reply-To: <20150703170229.GJ3291@awork2.anarazel.de>
* 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