Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Bruce Momjian <bruce@momjian.us>, Ashutosh Sharma <ashu.coek88@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>, Ajin Cherian <itsajin@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2023-09-06T08:48:52Z
Lists: pgsql-hackers 
On Fri, Sep 1, 2023 at 1:59 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi Shveta. Here are some comments for patch v14-0002
>
> The patch is large, so my code review is a WIP... more later next week...
>

Thanks Peter for the feedback. I have tried to address most of these
in v15. Please find my response inline for the ones which I have not
addressed.

> ======
> GENERAL
>
> 1. Patch size
>
> The patch is 2700 lines.  Is it possible to break this up into smaller
> self-contained parts to make the reviews more manageable?
>

Currently, patches are created based on work done on primary and
standby. Patch 001 for primary-side implementation and 002 for standby
side. Let me think more on this and see if the changes can be
segregated further.


>
> 26.
> +typedef struct SlotSyncWorker
> +{
> + /* Time at which this worker was launched. */
> + TimestampTz launch_time;
> +
> + /* Indicates if this slot is used or free. */
> + bool in_use;
> +
> + /* The slot in worker pool to which it is attached */
> + int slot;
> +
> + /* Increased every time the slot is taken by new worker. */
> + uint16 generation;
> +
> + /* Pointer to proc array. NULL if not running. */
> + PGPROC    *proc;
> +
> + /* User to use for connection (will be same as owner of subscription). */
> + Oid userid;
> +
> + /* Database id to connect to. */
> + Oid dbid;
> +
> + /* Count of Database ids it manages */
> + uint32 dbcount;
> +
> + /* DSA for dbids */
> + dsa_area *dbids_dsa;
> +
> + /* dsa_pointer for database ids it manages */
> + dsa_pointer dbids_dp;
> +
> + /* Mutex to access dbids in dsa */
> + slock_t         mutex;
> +
> + /* Info about slot being monitored for worker's naptime purpose */
> + SlotSyncWorkerWatchSlot monitor;
> +} SlotSyncWorker;
>
> There seems an awful lot about this struct which is common with
> 'LogicalRepWorker' struct.
>
> It seems a shame not to make use of the commonality instead of all the
> cut/paste here.
>
> E.g. Can it be rearranged so all these common fields are shared:
> - launch_time
> - in_use
> - slot
> - generation
> - proc
> - userid
> - dbid
>
> ======
> src/include/storage/lwlock.h

Sure, I had this in mind along with previous comments where it was
suggested to merge similar functions like
WaitForReplicationWorkerAttach, WaitForSlotSyncWorkerAttach etc. That
merging could only be possible if we try to merge the common part of
these structures. This is WIP, will be addressed in the next version.

>
> 27.
>   LWTRANCHE_LAUNCHER_HASH,
> - LWTRANCHE_FIRST_USER_DEFINED
> + LWTRANCHE_FIRST_USER_DEFINED,
> + LWTRANCHE_SLOT_SYNC_DSA
>  } BuiltinTrancheIds;
>
> Isn't 'LWTRANCHE_FIRST_USER_DEFINED' supposed to the be last enum?
>
> ======
> src/test/recovery/meson.build
>
> ======
> src/test/recovery/t/051_slot_sync.pl
>

I have currently removed this file from the patch. Please see my
comments (pt 3) here:
https://mail.google.com/mail/u/0/?ik=52d5778aba&view=om&permmsgid=msg-a:r-2984462571505788980

thanks
Shveta

> 28.
> +
> +# Copyright (c) 2021, PostgreSQL Global Development Group
> +
> +use strict;
>
> Wrong copyright date
>
> ~~~
>
> 29.
> +my $node_primary = PostgreSQL::Test::Cluster->new('primary');
> +my $node_phys_standby = PostgreSQL::Test::Cluster->new('phys_standby');
> +my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
>
> 29a.
> Can't all the subroutines be up-front? Then this can move to be with
> the other node initialisation code that comets next.
>
> ~
>
> 29b.
> Add a comment something like # Setup nodes
>
> ~~~
>
> 30.
> +# Check conflicting status in pg_replication_slots.
> +sub check_slots_conflicting_status
> +{
> + my $res = $node_phys_standby->safe_psql(
> + 'postgres', qq(
> + select bool_and(conflicting) from pg_replication_slots;));
> +
> + is($res, 't',
> + "Logical slot is reported as conflicting");
> +}
>
> Doesn't bool_and() mean returns false if only some but not all slots
> are conflicting - is that intentional?> Or is this sub-routine only
> expecting to test one slot, in which case maybe the SQL should include
> also the 'slot_name'?
>
> ~~~
>
> 31.
> +$node_primary->start;
> +$node_primary->psql('postgres', q{SELECT
> pg_create_physical_replication_slot('pslot1');});
> +
> +$node_primary->backup('backup');
> +
> +$node_phys_standby->init_from_backup($node_primary, 'backup',
> has_streaming => 1);
> +$node_phys_standby->append_conf('postgresql.conf', q{
> +synchronize_slot_names = '*'
> +primary_slot_name = 'pslot1'
> +hot_standby_feedback = off
> +});
> +$node_phys_standby->start;
> +
> +$node_primary->safe_psql('postgres', "CREATE TABLE t1 (a int PRIMARY KEY)");
> +$node_primary->safe_psql('postgres', "INSERT INTO t1 VALUES (1), (2), (3)");
>
> The comments seem mostly to describe details about what are the
> expectations at each test step.
>
> IMO there also needs to be a larger "overview" comment to describe
> more generally *what* this is testing, and *how* it is testing it.
> e.g. it is hard to understand the test without being already familiar
> with the patch.
>
> ------
> Kind Regards,
> Peter Smith.
> Fujitsu Australia

Commits

  1. Doc: Add the new section "Logical Replication Failover".

  2. Fix the review comments and a bug in the slot sync code.

  3. Fix a test in failover slots regression test.

  4. Fix the intermittent buildfarm failures in 040_standby_failover_slots_sync.

  5. Split XLogCtl->LogwrtResult into separate struct members

  6. Ensure that the sync slots reach a consistent state after promotion without losing data.

  7. Introduce a new GUC 'standby_slot_names'.

  8. Fix BF failure introduced by commit b3f6b14cf4.

  9. Fixups for commit 93db6cbda0.

  10. Fix BF failure in commit 93db6cbda0.

  11. Add a new slot sync worker to synchronize logical slots.

  12. Improve ERROR/LOG messages added by commits ddd5f4f54a and 7a424ece48.

  13. Disable autovacuum on primary in 040_standby_failover_slots_sync test.

  14. Fix the incorrect format specifier used in commit 7a424ece48.

  15. Change the LOG level in 040_standby_failover_slots_sync.pl to DEBUG2.

  16. Add more LOG and DEBUG messages for slot synchronization.

  17. Another try to fix BF failure introduced in commit ddd5f4f54a.

  18. Fix BF introduced in commit ddd5f4f54a.

  19. Add a slot synchronization function.

  20. Clean-ups for 776621a5e4 and 7329240437.

  21. Enhance libpqrcv APIs to support slot synchronization.

  22. Add a failover option to subscriptions.

  23. Allow setting failover property in the replication command.

  24. Allow to enable failover property for replication slots via SQL API.

  25. Add macros for looping through a List without a ListCell.

  26. Track conflict_reason in pg_replication_slots.

  27. Allow upgrades to preserve the full subscription's state.

  28. Add support for incremental backup.

  29. Simplify some logic in CreateReplicationSlot()

  30. Fix uninitialized access to InitialRunningXacts during decoding after ERROR.

  31. Flexible options for CREATE_REPLICATION_SLOT.

  32. Empty search_path in logical replication apply worker and walsender.

  33. Fix oldest xmin and LSN computation across repslots after advancing

  34. Require C99 (and thus MSCV 2013 upwards).