Re: Single transaction in the tablesync worker?

Hi Amit.

PSA the v16 patch for the Tablesync Solution1.

Main differences from v15:
+ Tablesync cleanups of DropSubscription/AlterSubscription_refresh are
re-implemented as as ProcessInterrupts function

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Features:

* The tablesync slot is now permanent instead of temporary.

* The tablesync slot name is no longer tied to the Subscription slot name.

* The tablesync worker is now allowing multiple tx instead of single tx

* A new state (SUBREL_STATE_FINISHEDCOPY) is persisted after a
successful copy_table in tablesync's LogicalRepSyncTableStart.

* If a re-launched tablesync finds state SUBREL_STATE_FINISHEDCOPY
then it will bypass the initial copy_table phase.

* Now tablesync sets up replication origin tracking in
LogicalRepSyncTableStart (similar as done for the apply worker). The
origin is advanced when first created.

* Cleanup of tablesync resources:
- The tablesync slot cleanup (drop) code is added for
process_syncing_tables_for_sync functions.
- The tablesync replication origin tracking is cleaned
process_syncing_tables_for_apply.
- A tablesync function to cleanup its own slot/origin is called from
ProcessInterrupt. This is indirectly invoked by
DropSubscription/AlterSubscrition when they signal the tablesync
worker to stop.

* Updates to PG docs.

TODO / Known Issues:

* Race condition observed in "make check" may be related to this patch.

* Add test cases.

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Please also see some test scenario logging which shows the new
tablesync cleanup function getting called as results of
Drop/AlterSUbscription.

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Kind Regards,
Peter Smith.
Fujitsu Australia