Horton

Re: Minimal logical decoding on standbys

Amit Khandekar <amitdkhan.pg@gmail.com>

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From: Amit Khandekar <amitdkhan.pg@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: tushar <tushar.ahuja@enterprisedb.com>, Petr Jelinek <petr.jelinek@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Petr Jelinek <petr@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-05-30T14:16:26Z
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.

On Mon, 27 May 2019 at 19:26, Andres Freund <andres@anarazel.de> wrote:
>
> On 2019-05-27 17:04:44 +0530, Amit Khandekar wrote:
> > On Fri, 24 May 2019 at 21:00, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> > >
> > > On Fri, 24 May 2019 at 19:26, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> > > > Working on the patch now ....
> > >
> > > Attached is an incremental WIP patch
> > > handle_wal_level_changes_WIP.patch to be applied over the earlier main
> > > patch logical-decoding-on-standby_v4_rebased.patch.
> >
> > I found an issue with these changes : When we change master wal_level
> > from logical to hot_standby, and again back to logical, and then
> > create a logical replication slot on slave, it gets created; but when
> > I do pg_logical_slot_get_changes() with that slot, it seems to read
> > records *before* I created the logical slot, so it encounters
> > parameter-change(logical=>hot_standby) record, so returns an error as
> > per the patch, because now in DecodeXLogOp() I error out when
> > XLOG_PARAMETER_CHANGE is found :
>
>
> > @@ -190,11 +190,23 @@ DecodeXLogOp(LogicalDecodingContext *ctx,
> > XLogRecordBuffer *buf)
> >              * can restart from there.
> >              */
> >             break;
> > +         case XLOG_PARAMETER_CHANGE:
> > +         {
> > +           xl_parameter_change *xlrec =
> > +             (xl_parameter_change *) XLogRecGetData(buf->record);
> > +
> > +           /* Cannot proceed if master itself does not have logical data */
> > +           if (xlrec->wal_level < WAL_LEVEL_LOGICAL)
> > +             ereport(ERROR,
> > +                 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> > +                  errmsg("logical decoding on standby requires "
> > +                     "wal_level >= logical on master")));
> > +           break;
> > +         }
> >
> > I thought it won't read records *before* the slot was created. Am I
> > missing something ?
>
> That's why I had mentioned that you'd need to adapt
> ReplicationSlotReserveWal(), to use the replay LSN or such.

Yeah ok. I tried to do this :

@@ -1042,7 +1042,8 @@ ReplicationSlotReserveWal(void)
 if (!RecoveryInProgress() && SlotIsLogical(slot))
 {
    ....
 }
 else
 {
-   restart_lsn = GetRedoRecPtr();
+   restart_lsn = SlotIsLogical(slot) ?
+                        GetXLogReplayRecPtr(&ThisTimeLineID) : GetRedoRecPtr();

But then when I do pg_create_logical_replication_slot(), it hangs in
DecodingContextFindStartpoint(), waiting to find new records
(XLogReadRecord).

Working on it ...



--
Thanks,
-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company