Re: Minimal logical decoding on standbys

Jeff Davis <pgsql@j-davis.com>

From: Jeff Davis <pgsql@j-davis.com>

To: Masahiko Sawada <sawada.mshk@gmail.com>

Cc: "Drouvot, Bertrand" <bertranddrouvot.pg@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: 2023-04-02T22:56:38Z

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 →

Reduce the log level in 035_standby_logical_decoding.pl.
- 3034dc56ef4b 16.0 landed
035_standby_logical_decoding: Add missing waits for replication
- 57411c82ce86 16.0 landed
For cascading replication, wake physical and logical walsenders separately
- e101dfac3a53 16.0 landed
Handle logical slot conflicts on standby
- 26669757b6a7 16.0 landed
Support invalidating replication slots due to horizon and wal_level
- be87200efd93 16.0 landed
Prevent use of invalidated logical slot in CreateDecodingContext()
- 4397abd0a2af 16.0 landed
Replace replication slot's invalidated_at LSN with an enum
- 15f8203a5975 16.0 landed
Pass down table relation into more index relation functions
- 61b313e47eb9 16.0 landed
Assert only valid flag bits are passed to visibilitymap_set()
- a88a18b1250b 16.0 landed
Remove unused _bt_delitems_delete() argument.
- dc43492e46c7 14.0 cited
Add xl_btree_delete optimization.
- d2e5e20e5711 13.0 cited

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