Re: Replication Issues

On 28/9/18 1:50 μ.μ., bhargav kamineni wrote:
> Ee are using 9.5 version, slot option -s is not available ,can I go with -X stream option ?
-S is intended when you plan to use the backup as a hot standby, when you must use the same replication slot.
If you plan to use the backup as a stand alone backup you don't need this option anyway.
>
> On Fri 28 Sep, 2018, 12:01 PM Laurenz Albe, <laurenz(dot)albe(at)cybertec(dot)at <mailto:laurenz(dot)albe(at)cybertec(dot)at>> wrote:
>
>  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
>

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Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt