On 12/27/24 13:20, Zhijie Hou (Fujitsu) wrote:
On Friday, December 27, 2024 7:39 PM Alexander Uvizhev<uvi...@posteo.net> wrote:
Hi,
I'm doing a logical replication using streaming replication protocol and
I'm trying to start a stream from a certain arbitrary point that's
available in WAL. However, both CREATE_REPLICATION_SLOT and
pg_create_logical_replication_slot() create slot with nearly last LSN/XID.
Is it possible to create a replication slot with arbitrary LSN/XID values?
I think it's not supported to specify arbitrary LSN/XID values for a newly
created slot in core. However, if you have an existing slot with an older
LSN/XID, you
can copy it using pg_copy_logical_replication_slot, and then advance the copied
slot to your desired position with pg_replication_slot_advance.
Thanks for the idea, I've already discovered it and it requires me to
implement some script to advance that dedicated slot, which I was hoping
to avoid.
Also pg_create_logical_replication_slot() for some reason gives
different result than CREATE_REPLICATION_SLOT: new slot's `catalog_xmin`
is set to the smallest `catalog_xmin` among already existing slots.
Looks like a bug.
Could you provide a script to reproduce this issue ?
That would be helpful in diagnosing the reason.
Unfortunately, I have no such script. But it looks like this:
test=> select slot_name, catalog_xmin, restart_lsn, confirmed_flush_lsn
from pg_replication_slots;
slot_name | catalog_xmin | restart_lsn | confirmed_flush_lsn
---------------+--------------+-------------+---------------------
inactive_slot | 10073 | 0/1101DB88 | 0/1101DB88
active_slot | 42607 | 0/17A87410 | 0/17A87410
physical | | 0/17A875A0 |
test=> select pg_create_logical_replication_slot('test_slot',
'decoderbufs');
slot_name | catalog_xmin | restart_lsn | confirmed_flush_lsn
---------------+--------------+-------------+---------------------
inactive_slot| 10073 | 0/1101DB88 | 0/1101DB88
active_slot | 42607 | 0/17A87410 | 0/17A87410
physical | | 0/17A875D8 |
test_slot | 10073 | 0/17A875A0 | 0/17A875D8
While using CREATE_REPLICATION_SLOT would give me the same slot with
`catalog_xmin` = 42607.
Hope this helps.
Best Regards,
Hou zj
--
AU
