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Re: Clarification on pg_basebackup - Mailing list pgsql-admin

From Jason Mathis
Subject Re: Clarification on pg_basebackup
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Msg-id etPan.54219a5f.2eb141f2.14be7@palos
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In response to Clarification on pg_basebackup  ("Campbell, Lance" <lance@illinois.edu>)
Responses Re: Clarification on pg_basebackup
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Hi Lance,

Maybe you want another view on it but I fear there is a slight miscommunication from our back and forth last week. 

Using the -x will get you to ONE POINT IN TIME. So if you backed up at 9PM you can restore back to that point and that point ONLY. Some people call this point in time, but its only ONE point in time. 

If you are archiving the wal files then you can restore to ANY POINT IN TIME. See the difference, its a big deal:) So if you backed up at 9PM and you need your database back to the state at 10am, no problem! Restore your 9PM and all the wal files until 10am. This is ANY POINT IN TIME. I feel the term "point in time” has gotten diluted and now there is two different “point in time;” one or any and that a huge difference.    

In all honestly it sounds to me you want ANY POINT IN TIME. So forget about the “-x” and just archive your wal files and its all good. Just make sure you have the base backup + all wal files until the point in time you want. So in order to keep three days of base backups you need at least three days of wal files as well. 

Make sense? 

On September 23, 2014 at 9:18:37 AM, Campbell, Lance (lance@illinois.edu) wrote:

PostgreSQL 9.3

Would someone be able to clarify if one should use the –X option with pg_basebackup when your intention is to include all WAL files created?  There are two scenarios.  The first scenario listed below makes sense using the –X option.  Bus scenario #2 has me a little confused.  I don’t want to cause any issues when restoring.

 

1)      Use pg_basebackup for a fully standalone restorable snapshot of the database using the –X parameter.  When a failure occurs you restore the database to that exact point in time.

2)      You restore from a pg_basebackup and you also apply all of the WAL files since the last pg_basebackup.  Do you want to use the –X option when doing the pg_basebackup if your intention is to have all of the WAL files since you backed up last?  Or does it matter.  Would PostgreSQL just ignore the duplicate WAL files that were created by the –X option during the pg_basebackup? 

 

Thanks for your clarification.  This is a hard scenario to test.

 

Thanks,

 

Lance Campbell

Software Architect

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217-333-0382

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