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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: Andres Freund <andres@anarazel.de>
Cc: 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: 2023-01-27T07:49:15Z
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 1/26/23 9:13 PM, Andres Freund wrote:
> Hi,
> 
> On 2023-01-26 18:56:10 +0100, Drouvot, Bertrand wrote:
>> - I'm struggling to create a test for btree killtuples as there is a need for rows removal on the table (that could produce a conflict too):
>> Do you've a scenario in mind for this one? (and btw in what kind of WAL record should the conflict be detected in such a case? xl_btree_delete?)
> 
> Hm, it might indeed be hard in "modern" postgres.  I think you'd need at least
> two concurrent sessions, to prevent on-access pruning on the table.
> 
> 
> DROP TABLE IF EXISTS indexdel;
> CREATE TABLE indexdel(id int8 primary key);
> INSERT INTO indexdel SELECT generate_series(1, 10000);
> VACUUM indexdel; -- ensure hint bits are set etc
> 
> DELETE FROM indexdel;
> 
> SELECT pg_current_wal_insert_lsn();
> 
> SET enable_indexonlyscan = false;
> -- This scan finds that the index items are dead - but doesn't yet issue a
> -- btree delete WAL record, that only happens when needing space on the page
> -- again.
> EXPLAIN (COSTS OFF, SUMMARY OFF) SELECT id FROM indexdel WHERE id < 10 ORDER BY id ASC;
> SELECT id FROM indexdel WHERE id < 100 ORDER BY id ASC;
> 
> -- The insertions into the range of values prev
> INSERT INTO indexdel SELECT generate_series(1, 100);
> 
> 
> Does generate the btree deletion record, but it also does emit a PRUNE (from
> heapam_index_fetch_tuple() -> heap_page_prune_opt()).
> 
> While the session could create a cursor to prevent later HOT cleanup, the
> query would also trigger hot pruning (or prevent the rows from being dead, if
> you declare the cursor before the DELETE). So you'd need overlapping cursors
> in a concurrent session...
> 

Thanks for the scenario and explanation!

I agree that a second session would be needed (and so I understand why I was
struggling when trying with a single session ;-) )

> Too complicated.
> 

Yeah.

Regards,

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