PITR - "Rewind to snapshot" scheme

"Martin Langhoff" <martin.langhoff@gmail.com> writes:

I have been following and experimenting a bit with PITR for a while,
and I wonder whether it is practical to use the PITR hooks to roll
back the database to a known state. The scenario is that I am
developing a script that will be massaging data in a medium size
database. A pg_restore of the pristine data takes ~35 minutes to
complete, if I can take a snapshot right after pg_restore, and use it
to later "rewind" to that point, I'll save 35 minutes every time I
need to test it.

Seems overly complicated --- why don't you just shut down the postmaster
and take a tarball archive of the PGDATA tree? Then to revert, stop
postmaster and untar.

regards, tom lane

On 4/17/07, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Seems overly complicated --- why don't you just shut down the postmaster
and take a tarball archive of the PGDATA tree? Then to revert, stop
postmaster and untar.

Thanks for the tip!

cheers

martin

Martin Langhoff wrote:

I have been following and experimenting a bit with PITR for a while,
and I wonder whether it is practical to use the PITR hooks to roll
back the database to a known state. The scenario is that I am
developing a script that will be massaging data in a medium size
database. A pg_restore of the pristine data takes ~35 minutes to
complete, if I can take a snapshot right after pg_restore, and use it
to later "rewind" to that point, I'll save 35 minutes every time I
need to test it.

The dev box where Pg runs has plenty of disk space to spare - and
it'll be a dedicated Pg instance. I've already raised wal_buffers to
20000 and also disabled wal fsync.

So my back-of-the-envelope plan is to

- run pg_restore
- setup wal archiving so that the logs aren't deleted
- pg_start_backup('label'); cp -pr pgdata pgdata-snapshot ;
pg_stop_backup('label')
- somehow remeber the transaction identifier

If it's the only database in the cluster (or you can make it so) then
it's probably simpler just to:
1. Get database to state you want
2. Stop postgresql
3. Take file-level backup of everything in $PGDATA
4. Restart postgresql
5. Run tests
6. Stop postgresql
7. Restore file-level backup
8. Go to step 4

--
Richard Huxton
Archonet Ltd

Or use a SAVEPOINT. I don't know about the impact on resources if you
leave it hanging around for a long time, but I use these for exactly
the scenario you are talking about.

- Ian