Horton

Re: [HACKERS] make async slave to wait for lsn to be replayed

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: Alexander Korotkov <aekorotkov@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Kartyshov Ivan <i.kartyshov@postgrespro.ru>, dilipbalaut@gmail.com, smithpb2250@gmail.com, pgsql-hackers@lists.postgresql.org
Date: 2024-03-21T22:58:06Z
Lists: pgsql-hackers 
On 17.03.24 15:09, Alexander Korotkov wrote:
> My current attempt was to commit minimal implementation as less
> invasive as possible.  A new clause for BEGIN doesn't require
> additional keywords and doesn't introduce additional statements.  But
> yes, this is still a new qual.  And, yes, Amit you're right that even
> if I had committed that, there was still a high risk of further
> debates and revert.

I had written in [0] about my questions related to using this with 
connection poolers.  I don't think this was addressed at all.  I haven't 
seen any discussion about how to make this kind of facility usable in a 
full system.  You have to manually query and send LSNs; that seems 
pretty cumbersome.  Sure, this is part of something that could be 
useful, but how would an actual user with actual application code get to 
use this?

[0]: 
https://www.postgresql.org/message-id/8b5b172f-0ae7-d644-8358-e2851dded43b%40enterprisedb.com

Commits

  1. Ensure standby promotion point in 043_wal_replay_wait.pl

  2. Minor cleanup related to pg_wal_replay_wait() procedure

  3. Adjust pg_wal_replay_wait() procedure behavior on promoted standby

  4. pg_wal_replay_wait(): Fix typo in the doc

  5. Implement pg_wal_replay_wait() stored procedure

  6. Revert: Implement pg_wal_replay_wait() stored procedure

  7. Call WaitLSNCleanup() in AbortTransaction()

  8. Clarify what is protected by WaitLSNLock

  9. Use an LWLock instead of a spinlock in waitlsn.c

  10. Use the pairing heap instead of a flat array for LSN replay waiters

  11. Minor improvements for waitlsn.c

  12. Make the order of the header file includes consistent