Re: Single transaction in the tablesync worker?

Hi Amit.

PSA my v9 WIP patch for the Solution1 which addresses some recent
review comments, and other minor changes.

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Features:

* tablesync slot is now permanent instead of temporary. The tablesync
slot name is no longer tied to the Subscription slot na

* the tablesync slot cleanup (drop) code is added for DropSubscription
and for finish_sync_worker functions

* tablesync worked now allowing multiple tx instead of single tx

* a new state (SUBREL_STATE_COPYDONE) is persisted after a successful
copy_table in LogicalRepSyncTableStart.

* if a relaunched tablesync finds the state is SUBREL_STATE_COPYDONE
then it will bypass the initial copy_table phase.

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

* tablesync replication origin tracking is cleaned up during
DropSubscription and/or process_syncing_tables_for_apply.

* The DropSubscription cleanup code was enhanced in v7 to take care of
crashed sync workers.

* Minor updates to PG docs

TODO / Known Issues:

* Source includes temporary "!!>>" excessive logging which I added to
help testing during development

* Address review comments

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Kind Regards,
Peter Smith.
Fujitsu Australia