Thread: Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
From
soumitra bhandary
Date:
Hi Pavan ,
Please try below query , this should give you retention lag bytes in case of logical replication .
SELECT
slot_name, database, active,
pg_xlog_location_diff(pg_current_xlog_insert_location(), restart_lsn) AS retained_bytes
FROM pg_replication_slots;Thanks ,
Soumitra
From: pavan95 <pavan.postgresdba@gmail.com>
Sent: Tuesday, October 9, 2018 11:29 AM
To: pgsql-admin@postgresql.org
Subject: Re: Null value returned by function pg_last_wal_receive_lsn() inLogical Replication
Sent: Tuesday, October 9, 2018 11:29 AM
To: pgsql-admin@postgresql.org
Subject: Re: Null value returned by function pg_last_wal_receive_lsn() inLogical Replication
Hi Community,
I configured Logical Replication in Postgres 10.5 using 2 nodes(Publisher
and Subscriber). I'm in my way to find lag in logical replication.
>From the documentation I found that, pg_current_wal_lsn() on the publisher
and pg_last_wal_receive_lsn() on the subscriber helps us to find the lag in
which the subscriber is falling behind.
But, the function pg_last_wal_receive_lsn() is continuously returning NULL
value. In fact, all the Recovery Information
Functions(pg_last_wal_receive_lsn(),pg_last_wal_replay_lsn(),pg_last_xact_replay_timestamp())
are returning null.
>From the Subscriber:
subscriber_db=# select pg_last_wal_receive_lsn();
pg_last_wal_receive_lsn
-------------------------
(1 row)
But according to documentation, the above 3 functions will return NULL only
if streaming replication is disabled or if it has not yet started. But in my
case, the logical replication is working fine. So I wanted to know if I
could get a value by enabling any settings recommended.
Also, is there a query to find the lag in bytes between publisher and
subscriber?
Thanks in Advance.
--
Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
I configured Logical Replication in Postgres 10.5 using 2 nodes(Publisher
and Subscriber). I'm in my way to find lag in logical replication.
>From the documentation I found that, pg_current_wal_lsn() on the publisher
and pg_last_wal_receive_lsn() on the subscriber helps us to find the lag in
which the subscriber is falling behind.
But, the function pg_last_wal_receive_lsn() is continuously returning NULL
value. In fact, all the Recovery Information
Functions(pg_last_wal_receive_lsn(),pg_last_wal_replay_lsn(),pg_last_xact_replay_timestamp())
are returning null.
>From the Subscriber:
subscriber_db=# select pg_last_wal_receive_lsn();
pg_last_wal_receive_lsn
-------------------------
(1 row)
But according to documentation, the above 3 functions will return NULL only
if streaming replication is disabled or if it has not yet started. But in my
case, the logical replication is working fine. So I wanted to know if I
could get a value by enabling any settings recommended.
Also, is there a query to find the lag in bytes between publisher and
subscriber?
Thanks in Advance.
--
Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
From
pavan95
Date:
Hi Soumitra, Could you please explain the reason behind taking the pg_current_xlog_insert_location() & restart_lsn? Regards, Pavan -- Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
From
pavan95
Date:
Community, Any help on this will be of great help! I am not able to understand why these functions return NULL values. Please let me know if I'm missing something. Thanks in Advance Regards, Pavan -- Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
From
Mark Kirkwood
Date:
I think those functions really only make sense for physical replication. Looking at the docs e.g: https://www.postgresql.org/docs/10/static/logical-replication-monitoring.html they appear to *suggest* that monitoring should be similar...some clarification there is probably in order! However they also say to use the pg_stat_subsubscription view to monitor your logical rep, e.g: here's what my pgbench dataset subscription looks like: bench=# SELECT * FROM pg_stat_subscription; subid | subname | pid | relid | received_lsn | last_msg_send_time | last_msg_receipt_time | latest_end_lsn | latest_end_time -------+---------+------+-------+--------------+-------------------------------+-------------------------------+----------------+------------------------------- 16409 | pgbench | 8840 | | 0/51EB3A20 | 2018-10-15 15:16:38.501061+13 | 2018-10-15 15:16:38.501103+13 | 0/51EB3A20 | 2018-10-15 15:16:38.501061+13 (1 row) Cheers Mark On 11/10/18 02:43, pavan95 wrote: > Hi Soumitra, > > Could you please explain the reason behind taking the > pg_current_xlog_insert_location() & restart_lsn? > > > Regards, > Pavan > > > > -- > Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html >
Re: Null value returned by function pg_last_wal_receive_lsn()inLogical Replication
From
soumitra bhandary
Date:
Hi Pavan ,
Yes as Mark explained , in logical replication no db server is in recovery mode and replication is happening through Replication slot . So no log shipping is involved here .
Hope this clarified your queries .
Thanks ,
Soumitra
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
Sent: Monday, October 15, 2018 7:52 AM
To: pgsql-admin@lists.postgresql.org
Subject: Re: Null value returned by function pg_last_wal_receive_lsn() inLogical Replication
Sent: Monday, October 15, 2018 7:52 AM
To: pgsql-admin@lists.postgresql.org
Subject: Re: Null value returned by function pg_last_wal_receive_lsn() inLogical Replication
I think those functions really only make sense for physical replication.
Looking at the docs e.g:
https://www.postgresql.org/docs/10/static/logical-replication-monitoring.html
they appear to *suggest* that monitoring should be similar...some
clarification there is probably in order!
However they also say to use the pg_stat_subsubscription view to monitor
your logical rep, e.g: here's what my pgbench dataset subscription looks
like:
bench=# SELECT * FROM pg_stat_subscription;
subid | subname | pid | relid | received_lsn |
last_msg_send_time | last_msg_receipt_time |
latest_end_lsn | latest_end_time
-------+---------+------+-------+--------------+-------------------------------+-------------------------------+----------------+-------------------------------
16409 | pgbench | 8840 | | 0/51EB3A20 | 2018-10-15
15:16:38.501061+13 | 2018-10-15 15:16:38.501103+13 | 0/51EB3A20 |
2018-10-15 15:16:38.501061+13
(1 row)
Cheers
Mark
On 11/10/18 02:43, pavan95 wrote:
> Hi Soumitra,
>
> Could you please explain the reason behind taking the
> pg_current_xlog_insert_location() & restart_lsn?
>
>
> Regards,
> Pavan
>
>
>
> --
> Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
>
Looking at the docs e.g:
https://www.postgresql.org/docs/10/static/logical-replication-monitoring.html
they appear to *suggest* that monitoring should be similar...some
clarification there is probably in order!
However they also say to use the pg_stat_subsubscription view to monitor
your logical rep, e.g: here's what my pgbench dataset subscription looks
like:
bench=# SELECT * FROM pg_stat_subscription;
subid | subname | pid | relid | received_lsn |
last_msg_send_time | last_msg_receipt_time |
latest_end_lsn | latest_end_time
-------+---------+------+-------+--------------+-------------------------------+-------------------------------+----------------+-------------------------------
16409 | pgbench | 8840 | | 0/51EB3A20 | 2018-10-15
15:16:38.501061+13 | 2018-10-15 15:16:38.501103+13 | 0/51EB3A20 |
2018-10-15 15:16:38.501061+13
(1 row)
Cheers
Mark
On 11/10/18 02:43, pavan95 wrote:
> Hi Soumitra,
>
> Could you please explain the reason behind taking the
> pg_current_xlog_insert_location() & restart_lsn?
>
>
> Regards,
> Pavan
>
>
>
> --
> Sent from: http://www.postgresql-archive.org/PostgreSQL-admin-f2076596.html
>