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Re: WAL file questions - how to relocate on Windows, how to replay after total loss, etc

From: "Douglas McNaught" <doug(at)mcnaught(dot)org>
To: "John T(dot) Dow" <john(at)johntdow(dot)com>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: WAL file questions - how to relocate on Windows, how to replay after total loss, etc
Date: 2008-08-28 19:45:41
Message-ID: 5ded07e00808281245j6c6fc7b6s99cf22ebb1feef11@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-general
On Thu, Aug 28, 2008 at 3:35 PM, John T. Dow <john(at)johntdow(dot)com> wrote:

> However, it would really be nice if the WAL files could be used to make the restored data more current, even if not everything can be restored. Are we certain that useful information can't be gleaned from them to apply changes made since the last pg_dump?

The WAL files contain changes at the disk block level, not the SQL
level.  A freshly created and restored database will have a totally
different block layout so WAL files would be useless.

The other thing you can do with WAL is "warm standby" -- creating a
duplicate server by copying the data files from the primary, then
arranging for the primary to ship each WAL file, once it's filled, to
the standby server, which is running in "permanent PITR" mode.  If the
primary server takes a dirt nap, you can bring up the standby and it
will be current as of the last WAL file that was shipped over.

For this to work, both machines must be the same architecture and have
identical versions of Postgres.

-Doug

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