Horton

Re: Minimal logical decoding on standbys

bdrouvotAWS <bdrouvot@amazon.com>

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From: "Drouvot, Bertrand" <bdrouvot@amazon.com>
To: <fabriziomello@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, tushar <tushar.ahuja@enterprisedb.com>, "[pgdg] Robert Haas" <robertmhaas@gmail.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, Rahila Syed <rahila.syed@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-03-23T11:47:29Z
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

On 3/22/21 4:56 PM, Drouvot, Bertrand wrote:
>
>
> On 3/22/21 3:57 PM, Drouvot, Bertrand wrote:
>>
>>
>> On 3/22/21 3:10 PM, Fabrízio de Royes Mello wrote:
>>>
>>> On Thu, Mar 18, 2021 at 5:34 AM Drouvot, Bertrand 
>>> <bdrouvot@amazon.com <mailto:bdrouvot@amazon.com>> wrote:
>>> >
>>> > Thanks!
>>> >
>>> > Just made minor changes to make it compiling again on current 
>>> master (mainly had to take care of 
>>> ResolveRecoveryConflictWithSnapshotFullXid() that has been 
>>> introduced in e5d8a99903).
>>> >
>>> > Please find enclosed the new patch version that currently passes 
>>> "make check" and the 2 associated TAP tests.
>>> >
>>>
>>> Unfortunately it still not applying to the current master:
>>>
>>> $ git am ~/Downloads/v10-000*.patch
>>> Applying: Allow logical decoding on standby.
>>> Applying: Add info in WAL records in preparation for logical slot 
>>> conflict handling.
>>> error: patch failed: src/backend/access/nbtree/nbtpage.c:32
>>> error: src/backend/access/nbtree/nbtpage.c: patch does not apply
>>> Patch failed at 0002 Add info in WAL records in preparation for 
>>> logical slot conflict handling.
>>> hint: Use 'git am --show-current-patch' to see the failed patch
>>> When you have resolved this problem, run "git am --continue".
>>> If you prefer to skip this patch, run "git am --skip" instead.
>>> To restore the original branch and stop patching, run "git am --abort".
>>
>> oh Indeed, it's moving so fast!
>>
>> Let me rebase it (It was already my plan to do so as I have observed 
>> during the week end that the 
>> v7-0003-Handle-logical-slot-conflicts-on-standby.patch 
>> <https://www.postgresql.org/message-id/attachment/117031/v7-0003-Handle-logical-slot-conflicts-on-standby.patch> 
>> introduced incorrect changes (that should not be there at all in 
>> ReplicationSlotReserveWal()) that have been kept in v8, v9 and v10.
>>
> please find enclosed the rebase version, that also contains the fix 
> for ReplicationSlotReserveWal() mentioned above.
>
> Going back to looking at the whole thread.
>
I have one remark regarding the conflicts:

The logical slots are dropped if a conflict is detected.

But, if the slot is not active before being dropped (say wal_level is 
changed to  < logical on master and a logical slot is not active on the 
standby) then its corresponding 
pg_stat_database_conflicts.confl_logicalslot is not incremented (as it 
would be incremented "only" during the cancel of an "active" backend).

I think, it should be incremented in all the cases (active or not), what 
do you think?

I updated the patch to handle this scenario (see the new 
pgstat_send_droplogicalslot() in 
v12-0003-Handle-logical-slot-conflicts-on-standby.patch).

I also added more tests in 023_standby_logical_decoding_conflicts.pl to 
verify that pg_stat_database_conflicts.confl_logicalslot is updated as 
expected (see check_confl_logicalslot() in 
v12-0004-New-TAP-test-for-logical-decoding-on-standby.patch).

Except this remark and the associated changes, then it looks good to me.

Bertrand