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Re: Stuck trying to backup large database - best practice?

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On 01/12/2015 08:10 AM, Antony Gelberg wrote:
<some snippage>

On Mon, Jan 12, 2015 at 5:31 PM, Adrian Klaver
<adrian.klaver@xxxxxxxxxxx> wrote:

On 01/12/2015 07:20 AM, Antony Gelberg wrote:

pg_basebackup: could not get transaction log end position from server:
ERROR: requested WAL segment 0000000400002B9F000000B4 has already been
removed

This attempted backup reached 430GB before failing.


It fails because the WAL file it needs has been removed from under it.


Okay.  We simply understood that it took too long.  Clearly we have a
lot to learn about WAL and its intricacies.

See here:

http://www.postgresql.org/docs/9.4/interactive/wal.html


We were advised on IRC to try -Xs, but that only works with a plain
(uncompressed) backup, and as you'll note from above, we don't have
enough disk space for this.

Is there anything else we can do apart from get a bigger disk (not
trivial at the moment)?  Any best practice?

What is the purpose of the backup?

In other words do really want the data and the WALs together or do you
just want the data?

No, we just want to be able to restore our data at a later point.  (As
as secondary point, it's not that clear to me why it would be useful
to have both, I'd be interested for some insight.)

Seems you may be better served by pg_dump:

http://www.postgresql.org/docs/9.4/interactive/app-pgdump.html

pg_basebackup has additional features which in your case are creating issues. pg_dump on the other hand is pretty much a straight forward data dump and if you use -Fc you get compression.

Something I failed to ask in my previous post, how are you determining the size of the database?

In addition are you talking about a single database or the Postgres database cluster?


Antony




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Adrian Klaver
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