Horton

Re: Minimal logical decoding on standbys

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Amit Khandekar <amitdkhan.pg@gmail.com>
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: 2019-04-12T19:27:47Z
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.

Hi,

On 2019-04-12 23:34:02 +0530, Amit Khandekar wrote:
> I tried to see if I can quickly understand what's going on.
> 
> Here, master wal_level is hot_standby, not logical, though slave
> wal_level is logical.

Oh, that's well diagnosed.  Cool.  Also nicely tested - this'd be ugly
in production.

I assume the problem isn't present if you set the primary to wal_level =
logical?


> Not sure why this is happening. On slave, wal_level is logical, so
> logical records should have tuple data. Not sure what does that have
> to do with wal_level of master. Everything should be there on slave
> after it replays the inserts; and also slave wal_level is logical.

The standby doesn't write its own WAL, only primaries do. I thought we
forbade running with wal_level=logical on a standby, when the primary is
only set to replica.  But that's not what we do, see
CheckRequiredParameterValues().

I've not yet thought this through, but I think we'll have to somehow
error out in this case.  I guess we could just check at the start of
decoding what ControlFile->wal_level is set to, and then raise an error
in decode.c when we pass an XLOG_PARAMETER_CHANGE record that sets
wal_level to something lower?

Could you try to implement that?

Greetings,

Andres Freund