Re: Single transaction in the tablesync worker?

On Thu, Dec 10, 2020 at 8:49 PM Peter Smith <smithpb2250@gmail.com> wrote:

> So I will try to write a patch for the proposed Solution-1.
>

Hi Amit.

FYI, here is my v3 WIP patch for the Solution1.

This patch applies onto the v30 patch set [1] from the other 2PC thread:
[1] https://www.postgresql.org/message-id/CAFPTHDYA8yE6tEmQ2USYS68kNt%2BkM%3DSwKgj%3Djy4AvFD5e9-UTQ%40mail.gmail.com

Although incomplete, it does continue to pass all the make check, and
src/test/subscription TAP tests.

====

Coded / WIP:

* tablesync slot is now permanent instead of temporary

* 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.


TODO / Known Issues:

* The tablesync replication origin/lsn logic all needs to be updated
so that tablesync knows where to restart based on information held by
the now permanent slot.

* the current implementation of tablesync drop slot (e.g. from DROP
SUBSCRIPTION) or finish_sync_worker regenerates the tablesync slot
name so it knows what slot to drop. The current code may be ok for
normal use cases, but if there is an ALTER SUBSCRIPTION ... SET
(slot_name = newname) it would fail to be able to find the tablesync
slot. Some redesign may be needed for this part.

* help / comments / cleanup

* There is temporary "!!>>" excessive logging of mine scattered around
which I added to help my testing during development

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Kind Regards,
Peter Smith.
Fujitsu Australia