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: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@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>, Alvaro Herrera <alvherre@alvh.no-ip.org>, shveta malik <shveta.malik@gmail.com>
Date: 2023-09-19T04:59:26Z
Lists: pgsql-hackers 
On Fri, Sep 15, 2023 at 2:22 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi. Here are some review comments for v17-0002.
>

Thanks Peter for the feedback.  I have addressed most of these in v18
except 2.  Please find my comments for the ones not addressed.

> This is a WIP and a long way from complete, but I wanted to send what
> I have so far (while it is still current with your latest posted
> patches).
>
> ======

>
> 34. ListSlotDatabaseOIDs - sorting/logic
>
> Maybe explain better the reason for having the qsort and other logic.
>
> TBH, I was not sure of the necessity for the names lists and the
> sorting and bsearch logic. AFAICT these are all *only* used to check
> for uniqueness and existence of the slot name. So I was wondering if a
> hashmap keyed by the slot name might be more appropriate and also
> simpler than all this list sorting/searching.
>

Pending. I will revisit this soon and will let you know more on this.
IMO, it was done to optimize the search as slot_names list could be
pretty huge if max_replication_slots is set to high value.

> ~~
>
> 35. ListSlotDatabaseOIDs
>
> + for (int slotno = 0; slotno < max_replication_slots; slotno++)
> + {
>
> loop variable declaration
>
>
> ======
> src/backend/storage/lmgr/lwlock.c
> OK
>
> ======
> src/backend/storage/lmgr/lwlocknames.txt
> OK
>
> ======
> .../utils/activity/wait_event_names.txt
> TODO
>
> ======
> src/backend/utils/misc/guc_tables.c
> OK
>
> ======
> src/backend/utils/misc/postgresql.conf.sample
>
> 36.
>   # primary to streaming replication standby server
> +#max_slotsync_workers = 2 # max number of slot synchronization
> workers on a standby
>
> IMO it is better to say "maximum" instead of "max" in the comment.
>
> (make sure the GUC description text is identical)
>
> ======
> src/include/catalog/pg_proc.dat
>
> 37.
> +{ oid => '6312', descr => 'get invalidate cause of a replication slot',
> +  proname => 'pg_get_invalidation_cause', provolatile => 's',
> proisstrict => 't',
> +  prorettype => 'int2', proargtypes => 'name',
> +  prosrc => 'pg_get_invalidation_cause' },
>
> 37a.
> SUGGESTION (descr)
> what caused the replication slot to become invalid
>
> ~
>
> 37b
> 'pg_get_invalidation_cause' seemed like a poor function name because
> it doesn't have any context -- not even the word "slot" in it.
>
> ======
> src/include/commands/subscriptioncmds.h
> OK
>
> ======
> src/include/nodes/replnodes.h
> OK
>
> ======
> src/include/postmaster/bgworker_internals.h
>
> 38.
>  #define MAX_PARALLEL_WORKER_LIMIT 1024
> +#define MAX_SLOT_SYNC_WORKER_LIMIT 50
>
> Consider SLOTSYNC instead of SLOT_SYNC for consistency with other
> names of this worker.
>
> ======
> OK
>
> ======
> src/include/replication/logicalworker.h
>
> 39.
>  extern void ApplyWorkerMain(Datum main_arg);
>  extern void ParallelApplyWorkerMain(Datum main_arg);
>  extern void TablesyncWorkerMain(Datum main_arg);
> +extern void ReplSlotSyncMain(Datum main_arg);
>
> The name is not consistent with others nearby. At least it should
> include the word "Worker" like everything else does.
>
> ======
> src/include/replication/slot.h
> OK
>
> ======
> src/include/replication/walreceiver.h
>
> 40.
> +/*
> + * Slot's DBid related data
> + */
> +typedef struct WalRcvRepSlotDbData
> +{
> + Oid database; /* Slot's DBid received from remote */
> + TimestampTz last_sync_time; /* The last time we tried to launch sync
> + * worker for above Dbid */
> +} WalRcvRepSlotDbData;
> +
>
>
> Is that comment about field 'last_sync_time' correct? I thought this
> field is the last time the slot was synced -- not the last time the
> worker was launched.

Sorry for confusion. Comment is correct, the name is misleading. I
have changed the name in v18.

>
> ======
> src/include/replication/worker_internal.h
>
> 41.
> - /* User to use for connection (will be same as owner of subscription). */
> + /* User to use for connection (will be same as owner of subscription
> + * in case of LogicalRep worker). */
>   Oid userid;
> +} WorkerHeader;
>
> 41a.
>
> This is not the normal style for a multi-line comment.
>
> ~
>
> 41b.
> I wondered if the name "WorkerHeader" is just a bit *too* generic and
> might cause future trouble because of the vague name.
>

I agree. Can you please suggest a better name for it?


thanks
Shveta

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).