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Re: Minimal logical decoding on standbys

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, fabriziomello@gmail.com, tushar <tushar.ahuja@enterprisedb.com>, Rahila Syed <rahila.syed@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-01-23T11:03:35Z
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. Reduce the log level in 035_standby_logical_decoding.pl.

  2. 035_standby_logical_decoding: Add missing waits for replication

  3. For cascading replication, wake physical and logical walsenders separately

  4. Handle logical slot conflicts on standby

  5. Support invalidating replication slots due to horizon and wal_level

  6. Prevent use of invalidated logical slot in CreateDecodingContext()

  7. Replace replication slot's invalidated_at LSN with an enum

  8. Pass down table relation into more index relation functions

  9. Assert only valid flag bits are passed to visibilitymap_set()

  10. Remove unused _bt_delitems_delete() argument.

  11. Add xl_btree_delete optimization.

Attachments

Hi,

On 1/19/23 10:43 AM, Drouvot, Bertrand wrote:
> Hi,
> 
> On 1/19/23 3:46 AM, Andres Freund wrote:
>> Hi,
>>
>> I mean a logical walsender that starts on a standby and continues across
>> promotion of the standby.
>>
> 
> Got it, thanks, will do.
> 

While working on it, I noticed that with V41 a:

pg_recvlogical -S active_slot -P test_decoding -d postgres -f - --start

on the standby is getting:

pg_recvlogical: error: unexpected termination of replication stream: ERROR:  could not find record while sending logically-decoded data: invalid record length at 0/311C438: wanted 24, got 0
pg_recvlogical: disconnected; waiting 5 seconds to try again

when the standby gets promoted (the logical decoding is able to resume correctly after the error though).

This is fixed in V42 attached (no error anymore and logical decoding through the walsender works correctly after the promotion).

The fix is in 0003 where in logical_read_xlog_page() (as compare to V41):

- We now check if RecoveryInProgress() (instead of relying on am_cascading_walsender) to check if the standby got promoted
- Based on this, the currTLI is being retrieved with GetXLogReplayRecPtr() or GetWALInsertionTimeLine() (so, with GetWALInsertionTimeLine() after promotion)
- This currTLI is being used as an argument in WALRead() (instead of state->seg.ws_tli, which anyhow sounds weird as being
  compared with itself that way "tli != state->seg.ws_tli" in WALRead()). That way WALRead() discovers that the timeline changed and then opens the right WAL file.

Please find V42 attached.

I'll resume working on the TAP tests comments.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com