Re: Replication Issues

bhargav kamineni wrote:
> Hi Team,
>
> I have configured replication using slot ,But it failed by throwing the
> ERROR pg_basebackup: could not get transaction log end position from server:
> ERROR: requested WAL segment 0000000100002C9D00000085 has already been removed ,
> which is unexpected because i have created the slot on master first
> and then issued the base backup command from slave's end
> the command is
> usr/lib/postgresql/9.5/bin/pg_basebackup -U user --max-rate='150 M' --progress --verbose --write-recovery-conf --status-interval='10 s' -D data_dir -h host_ip -p 5433
> These are the settings on my master
> archive_mode=on
> archive_command='/bin/true'
> wal_keep_segments=512
> max_wal_senders=4
> Series of steps i have followed :
> 1) Enabled password less authentication between master and slave
> 2)created slot on master (assuming it will store wal's regardless of other settings)
> 3)started basebackup from slave's end
> 4)Issued checkpoint at master's end
>
> Here my concern is , slave should recover WAL from replication slot but why i
> got the above ERROR , Why slot removed the requested wal file , Could you please
> let me know the reason why it happened or did i miss something ?

I guess your base backup took long enough for the required WAL segments to be
removed by the time it was done.

To prevent that, create a replication slot *before* you perform pg_basebackup
and use the options "-S <slotname> -X stream" of pg_basebackup.

You then use the same slot in "recovery.conf".

That way you cannot lose any WAL.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com