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From: Jeff Davis <[email protected]>
To: Masahiko Sawada <[email protected]>
Cc: Drouvot, Bertrand <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Ibrar Ahmed <[email protected]>
Cc: Amit Khandekar <[email protected]>
Cc: [email protected]
Cc: tushar <[email protected]>
Cc: Rahila Syed <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Minimal logical decoding on standbys
Date: Sun, 02 Apr 2023 15:56:38 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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	<[email protected]>

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?

Regards,
	Jeff Davis

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