Re: increasing the default WAL segment size

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
Cc: David Steele <david(at)pgmasters(dot)net>, Stephen Frost <sfrost(at)snowman(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, tushar <tushar(dot)ahuja(at)enterprisedb(dot)com>, Prabhat Sahu <prabhat(dot)sahu(at)enterprisedb(dot)com>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: increasing the default WAL segment size
Date: 2017-03-24 01:47:45
Message-ID: CAMkU=1wdfFc_WQFzgVC-fNXPi+G3XmWPt_mUe0JKDgwaCSLepQ@mail.gmail.com
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On Thu, Mar 23, 2017 at 1:45 PM, Peter Eisentraut <
peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:

> On 3/22/17 17:33, David Steele wrote:
>
> > and I doubt that most tool writers would be quick to
> > add support for a feature that very few people (if any) use.
>
> I'm not one of those tool writers, although I have written my share of
> DBA scripts over the years, but I wonder why those tools would really
> care. They are handed files with predetermined names to archive, and
> for restore files with predetermined names are requested back from them.
> What else do they need? If something is missing that requires them to
> parse file names, then maybe that should be added.
>

I have a pg_restore which predicts the file 5 files ahead of the one it was
asked for, and initiates a pre-fetch and decompression of it. Then it
delivers the file it was asked for, either by pulling it out of the
pre-staging area set up by the N-5th invocation, or by going directly to
the archive to get it. This speeds up play-back dramatically when the
files are stored compressed and non-local.

That is why I need to know how the files are numbered. I don't think that
that makes much of a difference, though. Any change is going to break
that, no matter which change. Then I'll fix it.

If we are going to break it, I'd prefer to just do away with the 'segment'
thing altogether. You have timelines, and you have files. That's it.

Cheers,

Jeff

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