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Wal file query

From

Atul Kumar

Date:

08 April, 14:44:07

In streaming replication What is the way to check which "WAL file" is currently in use in primary and in standby ?

Regards.

Re: Wal file query

From

Kashif Zeeshan

Date:

08 April, 15:01:38

Hi Atul

Start by looking at the current WAL LSN and insert LSN. The pg_current_wal_lsn is the location of the last write. The pg_current_wal_insert_lsn is the logical location and reflects data in the buffer that has not been written to disk. There is also a flush value that shows what has been written to durable storage.

[postgres] # select pg_current_wal_lsn(), pg_current_wal_insert_lsn(); pg_current_wal_lsn | pg_current_wal_insert_lsn
--------------------+--------------------------- 76/7D000000        | 76/7D000028
(1 row)

Although you can guess the name of the WAL file based on the above output, it is best to use the pg_walfile_name function.

[postgres] # select pg_walfile_name('76/7D000028');     pg_walfile_name
-------------------------- 00000001000000760000007D
(1 row)

For details visit following link : https://www.crunchydata.com/blog/postgres-wal-files-and-sequuence-numbers

Thanks
Kashif Zeeshan

On Tue, Apr 8, 2025 at 4:44 PM Atul Kumar <akumar14871@gmail.com> wrote:

In streaming replication What is the way to check which "WAL file" is currently in use in primary and in standby ?

Regards.

Re: Wal file query

From

Atul Kumar

Date:

08 April, 16:09:01

I got the error:

Wal control functions cannot be executed during recovery.

I need the solution that should in when streaming replication is configured.

My postgres version is 13.20

Regards.

On Tue, 8 Apr 2025, 17:32 Kashif Zeeshan, <kashi.zeeshan@gmail.com> wrote:

Hi Atul

[postgres] # select pg_current_wal_lsn(), pg_current_wal_insert_lsn(); pg_current_wal_lsn | pg_current_wal_insert_lsn
--------------------+--------------------------- 76/7D000000        | 76/7D000028
(1 row)

Although you can guess the name of the WAL file based on the above output, it is best to use the pg_walfile_name function.

[postgres] # select pg_walfile_name('76/7D000028');     pg_walfile_name
-------------------------- 00000001000000760000007D
(1 row)

For details visit following link : https://www.crunchydata.com/blog/postgres-wal-files-and-sequuence-numbers

Thanks
Kashif Zeeshan

On Tue, Apr 8, 2025 at 4:44 PM Atul Kumar <akumar14871@gmail.com> wrote:

In streaming replication What is the way to check which "WAL file" is currently in use in primary and in standby ?

Regards.

Re: Wal file query

From

Ron Johnson

Date:

08 April, 16:32:06

You cannot connect to the Primary while connected to the Replica, except via postgres_fdw. Even then, it might not work, since the replica replicates _fdw definitions.

These exist on the primary:

pg_current_wal_lsn()
pg_replication_slots
pg_stat_replication

These exist on the replica:

pg_last_wal_receive_lsn()
pg_last_wal_replay_lsn()
pg_stat_wal_receiver
pg_get_wal_replay_pause_state()

On Tue, Apr 8, 2025 at 9:09 AM Atul Kumar <akumar14871@gmail.com> wrote:

I got the error:

Wal control functions cannot be executed during recovery.

I need the solution that should in when streaming replication is configured.

My postgres version is 13.20

Regards.
On Tue, 8 Apr 2025, 17:32 Kashif Zeeshan, <kashi.zeeshan@gmail.com> wrote:
Hi Atul

Start by looking at the current WAL LSN and insert LSN. The pg_current_wal_lsn is the location of the last write. The pg_current_wal_insert_lsn is the logical location and reflects data in the buffer that has not been written to disk. There is also a flush value that shows what has been written to durable storage.
[postgres] # select pg_current_wal_lsn(), pg_current_wal_insert_lsn(); pg_current_wal_lsn | pg_current_wal_insert_lsn
--------------------+--------------------------- 76/7D000000        | 76/7D000028
(1 row)
Although you can guess the name of the WAL file based on the above output, it is best to use the pg_walfile_name function.
[postgres] # select pg_walfile_name('76/7D000028');     pg_walfile_name
-------------------------- 00000001000000760000007D
(1 row)

For details visit following link : https://www.crunchydata.com/blog/postgres-wal-files-and-sequuence-numbers

Thanks
Kashif Zeeshan
On Tue, Apr 8, 2025 at 4:44 PM Atul Kumar <akumar14871@gmail.com> wrote:
In streaming replication What is the way to check which "WAL file" is currently in use in primary and in standby ?

Regards.

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