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: Amit Kapila <amit.kapila16@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Jeff Davis <pgsql@j-davis.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>, Melanie Plageman <melanieplageman@gmail.com>
Date: 2023-04-02T08:11:52Z
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 4/1/23 6:50 AM, Amit Kapila wrote:
> On Fri, Mar 31, 2023 at 7:14 PM Drouvot, Bertrand
> <bertranddrouvot.pg@gmail.com> wrote:
>>
>> That sounds like a good idea. We could imagine creating a LogicalWalSndWakeup()
>> doing the Walsender(s) triage based on a new variable (as you suggest).
>>
>> But, it looks to me that we:
>>
>> - would need to go through the list of all the walsenders to do the triage
>> - could wake up some logical walsender(s) unnecessary
>>
> 
> Why it could wake up unnecessarily?

I was thinking that, if a new LogicalWalSndWakeup() replaces "ConditionVariableBroadcast(&XLogRecoveryCtl->replayedCV);"
in ApplyWalRecord() then, it could be possible that some walsender(s)
are requested to wake up while they are actually doing decoding (but I might be wrong).

> 
>> This extra work would occur during each replay.
>>
>> while with the CV, only the ones in the CV wait queue would be waked up.
>>
> 
> Currently, we wake up walsenders only after writing some WAL records
> at the time of flush, so won't it be better to wake up only after
> applying some WAL records rather than after applying each record?

Yeah that would be better.

Do you have any idea about how (and where) we could define the "some WAL records replayed"?

Regards,

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