Horton

Re: Minimal logical decoding on standbys

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, fabriziomello@gmail.com, tushar <tushar.ahuja@enterprisedb.com>, Rahila Syed <rahila.syed@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-01-24T14:31:24Z
Lists: pgsql-hackers

Commits

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  1. Reduce the log level in 035_standby_logical_decoding.pl.

  2. 035_standby_logical_decoding: Add missing waits for replication

  3. For cascading replication, wake physical and logical walsenders separately

  4. Handle logical slot conflicts on standby

  5. Support invalidating replication slots due to horizon and wal_level

  6. Prevent use of invalidated logical slot in CreateDecodingContext()

  7. Replace replication slot's invalidated_at LSN with an enum

  8. Pass down table relation into more index relation functions

  9. Assert only valid flag bits are passed to visibilitymap_set()

  10. Remove unused _bt_delitems_delete() argument.

  11. Add xl_btree_delete optimization.

Hi,

On 1/24/23 6:20 AM, Drouvot, Bertrand wrote:
> Hi,
> 
> On 1/24/23 1:46 AM, Andres Freund wrote:
>> Hi,
>>
>> On 2023-01-19 10:43:27 +0100, Drouvot, Bertrand wrote:
>>> Sure, so with:
>>>
>>> 1) hot_standby_feedback set to off on the standby
>>> 2) create 2 logical replication slots on the standby and activate one
>>> 3) Invalidate the logical slots on the standby with VACUUM FULL on the primary
>>> 4) change hot_standby_feedback to on on the standby
>>>
>>> If:
>>>
>>> 5) pg_reload_conf() on the standby, then on the primary we get a catalog_xmin
>>> for the physical slot that the standby is attached to:
>>>
>>> postgres=# select slot_type,xmin,catalog_xmin  from pg_replication_slots ;
>>>   slot_type | xmin | catalog_xmin
>>> -----------+------+--------------
>>>   physical  |  822 |          748
>>> (1 row)
>>
>> How long did you wait for this to change? 
> 
> Almost instantaneous after pg_reload_conf() on the standby.
> 
>> I don't think there's anything right
>> now that'd force a new hot-standby-feedback message to be sent to the primary,
>> after slots got invalidated.
>>
>> I suspect that if you terminated the walsender connection on the primary,
>> you'd not see it anymore either?
>>
> 
> Still there after the standby is shutdown but disappears when the standby is re-started.
> 
>> If that isn't it, something is broken in InvalidateObsolete...
>>

Yeah, you are right: ReplicationSlotsComputeRequiredXmin() is missing for the
logical slot invalidation case (and ReplicationSlotsComputeRequiredXmin() also
needs to take care of it).

I'll provide a fix in the next revision along with the TAP tests comments addressed.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com