Re: Wal files - Question | Postgres 9.2 - Mailing list pgsql-general

 

On Wed, Nov 23, 2016 at 1:59 PM, Patrick B <patrickbakerbr@gmail.com> wrote:

2016-11-23 15:55 GMT+13:00 Venkata B Nagothi <nag1010@gmail.com>:

On Wed, Nov 23, 2016 at 1:03 PM, Patrick B <patrickbakerbr@gmail.com> wrote:

Hi guys,

I currently have a slave02 server that is replicating from another slave01 via Cascading replication. The master01 server is shipping wal_files (via ssh) to both slaves. 

I'm doing some tests on slave02 to test the recovery via wal_files... The goal here is to stop postgres, wait few minutes, start postgres again, watch it recovering from wal_files, once it's done see the streaming replication start working again.

1 - Stop postgres on slave02(streaming replication + wal_files)

2 - Wait for 5 minutes

3 - Start postgres - The goal here is to tail the logs to see if the wal_files are being successfully recovered

However, when doing step3 I get these messages:

cp: cannot stat '/walfiles/0000000200001AF8000000A4': No such file or directory

cp: cannot stat '/walfiles/0000000200001AF8000000A5': No such file or directory

cp: cannot stat '/walfiles/0000000200001AF8000000A6': No such file or directory

LOG:  consistent recovery state reached at 1AF8/AB629F90

LOG:  database system is ready to accept read only connections

LOG:  streaming replication successfully connected to primary

still on slave01: Sometimes the log_delay time is bigger.. sometimes is lower

SELECT CASE WHEN pg_last_xlog_receive_location() = pg_last_xlog_replay_location() THEN 0 ELSE EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp()) END AS log_delay;

 log_delay

-----------

  0.386863

On master01:

select * from pg_current_xlog_location();

 pg_current_xlog_location

--------------------------

 1AF8/D3F47A80

QUESTION:

So.. I just wanna understand what's the risk of those errors... what's happening? 

cp: cannot stat '/walfiles/0000000200001AF8000000A5': No such file or directory - Means it didn't find the file. However, the file exists on the Master, but it didn't start shipping yet. What are the consequences of that?

That is just saying that the slave cannot find the WAL file. That should not be of big importance. Eventually, that will vanish when the log file gets shipped from the master. Also "cp: cannot stat." errors have been been fixed in 9.3 i believe.

Hi Venkata !

Yeah that's fine.. the streaming replication is already working fine.

But, as it didn't find/recover some of the wal_files, doesn't that mean that the DB isn't up-to-date?

Not necessarily. Standby periodically checks if the WAL file it is looking for is available at restore_command location and generates that message if the file is not available. These messages are not of any harm.

Below link might help you :

https://www.postgresql.org/message-id/4DDC9515.2000003%40enterprisedb.com