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Date: Mon, 14 Apr 2014 12:39:57 -0400
From: Jim Mercer <jim@reptiles.org>
To: pgsql-admin@postgresql.org
Subject: streaming replication - pgsql 9.2.3
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Hi,

I have set up streaming replication between two servers, using the various
walkthroughs the googlepedia found for me.

At this point, it certainly seems that the replication is working, and I am
able to actually blow away the slave, and have it rebuild, resync and be back
in action as a read-only source.

I am confused about the purpose and/or point of the WAL files in the context
of streaming replication.

The documentation seems to be quite insistent that the 'archive_command' should
be enabled on the master, and the 'restore_command' should be enabled on the
slave.

On the master, I made my own script which is fairly pedantic:
- copy the WAL file from $PGDATA/pg_xlog into $MASTER:$ARCHDIR
- rsync file(s) from $MASTER:$ARCHDIR to $SLAVE:$ARCHDIR
- remove copy of file in $MASTER:$ARCHDIR
(i don't have a network share between then, so, i am rsyncing)

On the slave, I made a similarly pedandic script:
- copy the file from $SLAVE:$ARCHDIR to $PGDATA/pg_xlog/RECOVERYXLOG

The script on the master runs with regularity, and i am seeing the WAL files
show up in $SLAVE:$ARCHDIR

however, on the slave side, i'm seeing some issues:

- the filename being handed to the script is sometimes for a non-existent file
- it appears to be the next file in sequence, but that filename hasn't even
been generated on the master yet.
- it appears, that if there are multiple files in $SLAVE:$ARCHDIR, they might
actually overwrite themselves when copied to pg_xlog/RECOVERYXLOG

these are the logs my script is generating, if i do a stop/start of postgres:

Apr 14 12:19:20 dt-pgsql-001 archive-slave.sh: notice: rtn=0 - cp [/export/pg-archive/00000001000000220000007F] /export/postgresql/data/main/[pg_xlog/RECOVERYXLOG]
Apr 14 12:19:20 dt-pgsql-001 archive-slave.sh: notice: rtn=0 - cp [/export/pg-archive/000000010000002200000080] /export/postgresql/data/main/[pg_xlog/RECOVERYXLOG]
Apr 14 12:19:23 dt-pgsql-001 archive-slave.sh: error: no such file[/export/pg-archive/000000010000002200000081]
Apr 14 12:19:23 dt-pgsql-001 archive-slave.sh: error: no such file[/export/pg-archive/000000010000002200000081]


am i doing something wrong?

please advise.


-- 
Jim Mercer     Reptilian Research      jim@reptiles.org    +1 416 410-5633
"He who dies with the most toys is nonetheless dead"


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