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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>, Jeff Davis <pgsql@j-davis.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Andres Freund <andres@anarazel.de>, 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: 2023-04-03T06:10:22Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  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 4/3/23 7:35 AM, Amit Kapila wrote:
> On Mon, Apr 3, 2023 at 4:26 AM Jeff Davis <pgsql@j-davis.com> wrote:
>>
>> On Fri, 2023-03-31 at 02:50 -0700, Jeff Davis wrote:
>>> But if the ConditionVariableEventSleep() API is added, then I think
>>> we
>>> should change the non-recovery case to use a CV as well for
>>> consistency, and it would avoid the need for WalSndWakeup().
>>
>> It seems like what we ultimately want is for WalSndWakeup() to
>> selectively wake up physical and/or logical walsenders depending on the
>> caller. For instance:
>>
>>     WalSndWakeup(bool physical, bool logical)
>>
>> The callers:
>>
>>    * On promotion, StartupXLog would call:
>>      - WalSndWakeup(true, true)
>>    * XLogFlush/XLogBackgroundFlush/XLogWalRcvFlush would call:
>>      - WalSndWakeup(true, !RecoveryInProgress())
>>    * ApplyWalRecord would call:
>>      - WalSndWakeup(switchedTLI, switchedTLI || RecoveryInProgress())
>>
>> There seem to be two approaches to making that work:
>>
>> 1. Use two ConditionVariables, and WalSndWakeup would broadcast to one
>> or both depending on its arguments.
>>
>> 2. Have a "replicaiton_kind" variable in WalSnd (either set based on
>> MyDatabaseId==InvalidOid, or set at START_REPLICATION time) to indicate
>> whether it's a physical or logical walsender. WalSndWakeup would wake
>> up the right walsenders based on its arguments.
>>
>> #2 seems simpler at least for now. Would that work?
>>
> 
> Agreed, even Bertrand and myself discussed the same approach few
> emails above. BTW, if we have this selective logic to wake
> physical/logical walsenders and for standby's, we only wake logical
> walsenders at the time of  ApplyWalRecord() then do we need the new
> conditional variable enhancement being discussed, and if so, why?
> 

Thank you both for this new idea and discussion. In that case I don't think
we need the new CV API and the use of a CV anymore. As just said up-thread I'll submit
a new proposal with this new approach.

Regards,

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