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Thread: Streaming Replication

Streaming Replication

From
ning chan
Date:
Hi,
I am new to PG Streaming Replication and I have a simple question hopefully someone can answer this easily.

I setup a Primary Hot Standby and they are connecting each other without problem.
Looking at the wal sender process, both servers pointing to the same location as follow:

Primary:
postgres  3018  0.0  0.1 203888  3024 ?        Ss   19:25   0:00 postgres: wal sender process postgres 10.89.94.31(43169) streaming 0/D913018

Standby:
postgres  3645  0.0  0.1 212556  3096 ?        Ss   19:25   0:00 postgres: wal receiver process   streaming 0/D913018

My question is when looking at the standby processes, I see startup process as follow:

postgres  3320  0.0  0.0 203048  2084 ?        Ss   18:11   0:00 postgres: startup process   recovering 00000001000000000000000D

What is that suppose to mean?
Is it really recovering some data from WAL record in the pg_xlog folder?

Thanks~
Ning


Re: Streaming Replication

From
Albe Laurenz
Date:
ning chan wrote:
> I am new to PG Streaming Replication and I have a simple question hopefully someone can answer this
> easily.
>
> I setup a Primary Hot Standby and they are connecting each other without problem.
> Looking at the wal sender process, both servers pointing to the same location as follow:
>
> Primary:
> postgres  3018  0.0  0.1 203888  3024 ?        Ss   19:25   0:00 postgres: wal sender process postgres
> 10.89.94.31(43169) streaming 0/D913018
>
> Standby:
> postgres  3645  0.0  0.1 212556  3096 ?        Ss   19:25   0:00 postgres: wal receiver process
> streaming 0/D913018
>
> My question is when looking at the standby processes, I see startup process as follow:
> postgres  3320  0.0  0.0 203048  2084 ?        Ss   18:11   0:00 postgres: startup process
> recovering 00000001000000000000000D
>
> What is that suppose to mean?
> Is it really recovering some data from WAL record in the pg_xlog folder?

That indicates the WAL segment that is currently being
recovered, but not that WAL is read from a file in pg_xlog.

Yours,
Laurenz Albe

Re: Streaming Replication

From
ning chan
Date:
Hi Albe,
Thanks for your kind response.
The wordings is confusing, it gives me impression that the recovery is going on.


On Tue, Jan 15, 2013 at 2:09 AM, Albe Laurenz <laurenz.albe@wien.gv.at> wrote:
ning chan wrote:
> I am new to PG Streaming Replication and I have a simple question hopefully someone can answer this
> easily.
>
> I setup a Primary Hot Standby and they are connecting each other without problem.
> Looking at the wal sender process, both servers pointing to the same location as follow:
>
> Primary:
> postgres  3018  0.0  0.1 203888  3024 ?        Ss   19:25   0:00 postgres: wal sender process postgres
> 10.89.94.31(43169) streaming 0/D913018
>
> Standby:
> postgres  3645  0.0  0.1 212556  3096 ?        Ss   19:25   0:00 postgres: wal receiver process
> streaming 0/D913018
>
> My question is when looking at the standby processes, I see startup process as follow:
> postgres  3320  0.0  0.0 203048  2084 ?        Ss   18:11   0:00 postgres: startup process
> recovering 00000001000000000000000D
>
> What is that suppose to mean?
> Is it really recovering some data from WAL record in the pg_xlog folder?

That indicates the WAL segment that is currently being
recovered, but not that WAL is read from a file in pg_xlog.

Yours,
Laurenz Albe

Re: Streaming Replication

From
Fujii Masao
Date:
On Wed, Jan 16, 2013 at 1:22 AM, ning chan <ninchan8328@gmail.com> wrote:
> Hi Albe,
> Thanks for your kind response.
> The wordings is confusing, it gives me impression that the recovery is going
> on.

Yes. Walreceiver receives the WAL records from the master server, and writes
them to the pg_xlog directory. Then the startup process reads the WAL records
from the pg_xlog directory, and replays them.

Regards,

--
Fujii Masao