Re: [RFC] Incremental backup v3: incremental PoC

Hi Marco,

On 16/01/15 16:55, Marco Nenciarini wrote:
> On 14/01/15 17:22, Gabriele Bartolini wrote:
> > 
> > My opinion, Marco, is that for version 5 of this patch, you:
> > 
> > 1) update the information on the wiki (it is outdated - I know you have
> > been busy with LSN map optimisation)
> 
> Done.
> 
> > 2) modify pg_basebackup in order to accept a directory (or tar file) and
> > automatically detect the LSN from the backup profile
> 
> New version of patch attached. The -I parameter now requires a backup
> profile from a previous backup. I've added a sanity check that forbid
> incremental file level backups if the base timeline is different from
> the current one.
> 
> > 3) add the documentation regarding the backup profile and pg_basebackup
> > 
> 
> Next on my TODO list.
> 
> > Once we have all of this, we can continue trying the patch. Some
> > unexplored paths are:
> > 
> > * tablespace usage
> 
> I've improved my pg_restorebackup python PoC. It now supports tablespaces.

About tablespaces, I noticed that any pointing to tablespace locations is lost during the recovery of an incremental backup changing the tablespace mapping (-T option). Here the steps I followed:

• creating and filling a test database obtained through pgbench
  

  psql -c "CREATE DATABASE pgbench" 
  pgbench -U postgres -i -s 5 -F 80 pgbench
  

• a first base backup with pg_basebackup:

  mkdir -p backups/$(date '+%d%m%y%H%M')/data && pg_basebackup -v -F p -D backups/$(date '+%d%m%y%H%M')/data -x
  

• creation of a new tablespace, alter the table "pgbench_accounts" to set the new tablespace:

  mkdir -p /home/gbroccolo/pgsql/tbls
  psql -c "CREATE TABLESPACE tbls LOCATION '/home/gbroccolo/pgsql/tbls'" 
  psql -c "ALTER TABLE pgbench_accounts SET TABLESPACE tbls" pgbench
  

• Doing some work on the database:

  pgbench -U postgres -T 120 pgbench
  

• a second incremental backup with pg_basebackup specifying the new location for the tablespace through the tablespace mapping:

  mkdir -p backups/$(date '+%d%m%y%H%M')/data backups/$(date '+%d%m%y%H%M')/tbls && pg_basebackup -v -F p -D backups/$(date '+%d%m%y%H%M')/data -x -I backups/2601151641/data/backup_profile -T /home/gbroccolo/pgsql/tbls=/home/gbroccolo/pgsql/backups/$(date '+%d%m%y%H%M')/tbls
  

• a recovery based on the tool pg_restorebackup.py attached in http://www.postgresql.org/message-id/54B9428E.9020001@2ndquadrant.it

  ./pg_restorebackup.py backups/2601151641/data backups/2601151707/data /tmp/data -T /home/gbroccolo/pgsql/backups/2601151707/tbls=/tmp/tbls
  

In the last step, I obtained the following stack trace:

Traceback (most recent call last):  File "./pg_restorebackup.py", line 74, in <module>    shutil.copy2(base_file, dest_file)  File "/home/gbroccolo/.pyenv/versions/2.7.5/lib/python2.7/shutil.py", line 130, in copy2    copyfile(src, dst)  File "/home/gbroccolo/.pyenv/versions/2.7.5/lib/python2.7/shutil.py", line 82, in copyfile    with open(src, 'rb') as fsrc:
IOError: [Errno 2] No such file or directory: 'backups/2601151641/data/base/16384/16406_fsm'