Re: Records count mismatch with logical replication

On Thu, Jan 23, 2025 at 10:08 PM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 1/22/25 18:53, Durgamahesh Manne wrote:
> >
> >
> >
>
> > > But records count varies with difference of more than 10 thousand
> >
> > Have you looked at the I/0 statistics between the Postgres instances?
> >
> > Seems everything looks good with pg replication slots
>
> Except the subscriber is lagging behind the publisher.
>
> '... everything looks good' is an opinion not actual data.
>
> >
> > Does this pg logical slot get changes function help to pull pending
> > changes to subscription that can be sync with publication server for
> > real time sync ?
>
> Are you referring to this?:
>
>
> https://www.postgresql.org/docs/current/warm-standby.html#SYNCHRONOUS-REPLICATION
>
> Though I am not sure you want to do this as from above:
>
> "When requesting synchronous replication, each commit of a write
> transaction will wait until confirmation is received that the commit has
> been written to the write-ahead log on disk of both the primary and
> standby server. The only possibility that data can be lost is if both
> the primary and the standby suffer crashes at the same time. This can
> provide a much higher level of durability, though only if the sysadmin
> is cautious about the placement and management of the two servers.
> Waiting for confirmation increases the user's confidence that the
> changes will not be lost in the event of server crashes but it also
> necessarily increases the response time for the requesting transaction.
> The minimum wait time is the round-trip time between primary and standby."
>
> If you are not referring to above then you will need to explain further.
>
> >
> > Regards,
> > Durgamahesh
> >
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com
>
>
Hi

Source Publication Side:
archiving=> select * from pg_replication_slots ;
-[ RECORD 1 ]-------+--------------
slot_name | cls_eva_msa
plugin | pgoutput
slot_type | logical
datoid | 16601
database | archiving
temporary | f
active | t
active_pid | 3237
xmin |
catalog_xmin | 2935229621
restart_lsn | 16C8/40CEC600
confirmed_flush_lsn | 16C8/440FFF50
wal_status | reserved
safe_wal_size |
two_phase | f
conflicting | f
-[ RECORD 2 ]-------+--------------
slot_name | cle_clm_mka
plugin | pgoutput
slot_type | logical
datoid | 16601
database | archiving
temporary | f
active | t
active_pid | 3501
xmin |
catalog_xmin | 2935229621
restart_lsn | 16C8/40CEC600
confirmed_flush_lsn | 16C8/440FFF50
wal_status | reserved
safe_wal_size |
two_phase | f
conflicting | f
archiving=> select * from pg_stat_replication;
client_hostname |
client_port | 52506
backend_start | 2025-01-23 16:58:04.697304+00
backend_xmin |
state | streaming
sent_lsn | 16C7/BDE4BB48
write_lsn | 16C7/BDE4BB48
flush_lsn | 16C7/BDE4BB48
replay_lsn | 16C7/BDE4BB48
write_lag | 00:00:00.002271
flush_lag | 00:00:00.002271
replay_lag | 00:00:00.002271
sync_priority | 0
sync_state | async
reply_time | 2025-01-23 17:34:39.901979+00
-[ RECORD 2 ]----+------------------------------
pid | 3501
usesysid | 14604130
usename | archiving
application_name | cle_clm_mka
client_addr | 10.80.0.168
client_hostname |
client_port | 55412
backend_start | 2025-01-22 09:31:11.83963+00
backend_xmin |
state | streaming
sent_lsn | 16C7/BDE4BB48
write_lsn | 16C7/BDE4BB48
flush_lsn | 16C7/BDE4BB48
replay_lsn | 16C7/BDE4BB48
write_lag | 00:00:00.001642
flush_lag | 00:00:00.023143
replay_lag | 00:00:00.001642
sync_priority | 0
sync_state | async
reply_time | 2025-01-23 17:34:39.903052+00

Subscription Side : archiving=> select * from pg_stat_subscription where
subname = 'cls_eva_msa';
-[ RECORD 1 ]---------+------------------------------
subid | 1936652827
subname | cls_eva_msa
pid | 18746
relid |
received_lsn | 16C7/FB48DFE0
last_msg_send_time | 2025-01-23 17:41:11.924562+00
last_msg_receipt_time | 2025-01-23 17:41:11.933344+00
latest_end_lsn | 16C7/FB48DFE0
latest_end_time | 2025-01-23 17:41:11.924562+00

archiving=> select * from pg_stat_subscription where subname =
'cle_clm_mka';
-[ RECORD 1 ]---------+------------------------------
subid | 1892055116
subname | cle_clm_mka
pid | 507
relid |
received_lsn | 16C7/FB8CDF68
last_msg_send_time | 2025-01-23 17:41:17.375879+00
last_msg_receipt_time | 2025-01-23 17:41:17.378932+00
latest_end_lsn | 16C7/FB8CDF68
latest_end_time | 2025-01-23 17:41:17.375879+00

If you need to see more stats based on your info will give you
Your response in this regard is valuable

Are you referring to this?:

https://www.postgresql.org/docs/current/warm-standby.html#SYNCHRONOUS-REPLICATION

No.I am using logical replication in asynchronous mode

Except the subscriber is lagging behind the publisher.

'... everything looks good' is an opinion not actual data.
Correct

Regards
Durga Mahesh