From: Josh Berkus <josh@agliodbs.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Greg Stark <gsstark@mit.edu>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Simplifying replication
Date: Fri, 22 Oct 2010 10:18:06 -0700
Message-ID: <4CC1C74E.8080409@agliodbs.com> (raw)
In-Reply-To: <AANLkTi=Nz06NGkUAEzJ7r=CMRsiUAJXRsWALqw-jZ62A@mail.gmail.com>
References: <201010220058.o9M0waa06053@momjian.us>
<4CC0E465.4000700@agliodbs.com>
<AANLkTineXrnRAkRV4Cs=rmSo0QkWkFRVYQpj0AWXGn2=@mail.gmail.com>
<4CC0F10D.3000201@agliodbs.com>
<AANLkTi=Nz06NGkUAEzJ7r=CMRsiUAJXRsWALqw-jZ62A@mail.gmail.com>
> Please see
> http://archives.postgresql.org/pgsql-docs/2010-10/msg00038.php
Ye gods and little fishes!
You really want to talk arcane formulas. I've re-read that
three times, and am still not sure that I could tell someone
definitively how much disk space WAL needs for a given group of
settings. I'll also point out that that formula is not in our docs --
what's an appropriate location?
I think this needs to be corrected in 9.1, *even if it means breaking
backwards compatibility*.
What would be sensible for DBAs is to have two settings:
max_wal_size
min_wal_size
These would be expresses in MB or GB and would be simple direct
quantities, which our formulas would work backwards from. max_wal_size
would be a hard limit (i.e. Postgres would stop accepting writes if we
hit it), and Admins would not be allowed to set min_wal_size to more
than max_wal_size - 2.
Even better would be to replace min_wal_size with min_wal_time, which
would set a time span for the oldest WAL segment to be kept (up to
max_wal_size - 2). Hmmm. That doesn't seem that hard to implement.
Is it?
(BTW, Robert, that e-mail is what I meant by "relationship")
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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To: pgsql-hackers@postgresql.org
Cc: josh@agliodbs.com, masao.fujii@gmail.com, robertmhaas@gmail.com, bruce@momjian.us, gsstark@mit.edu
Subject: Re: Simplifying replication
In-Reply-To: <4CC1C74E.8080409@agliodbs.com>
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