Horton

Re: logical decoding and replication of sequences, take 2

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: John Naylor <john.naylor@enterprisedb.com>, vignesh C <vignesh21@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: 2023-03-18T15:19:53Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Migrate logical slots to the new node during an upgrade.

  2. Make test_decoding ddl.out shorter

  3. Fix snapshot handling in logicalmsg_decode

  4. doc: Adjust a few more references to "postmaster"

  5. Revert "Logical decoding of sequences"

On 3/18/23 06:35, Amit Kapila wrote:
> On Sat, Mar 18, 2023 at 3:13 AM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
>>
>> ...
>>
>> Clearly, for sequences we can't quite rely on snapshots/slots, we need
>> to get the LSN to decide what changes to apply/skip from somewhere else.
>> I wonder if we can just ignore the queued changes in tablesync, but I
>> guess not - there can be queued increments after reading the sequence
>> state, and we need to apply those. But maybe we could use the page LSN
>> from the relfilenode - that should be the LSN of the last WAL record.
>>
>> Or maybe we could simply add pg_current_wal_insert_lsn() into the SQL we
>> use to read the sequence state ...
>>
> 
> What if some Alter Sequence is performed before the copy starts and
> after the copy is finished, the containing transaction rolled back?
> Won't it copy something which shouldn't have been copied?
> 

That shouldn't be possible - the alter creates a new relfilenode and
it's invisible until commit. So either it gets committed (and then
replicated), or it remains invisible to the SELECT during sync.


regards

-- 
Tomas Vondra
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