On Sat, 13 Apr 2019 at 00:57, Andres Freund <and...@anarazel.de> wrote: > > 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.
Tushar had made me aware of the fact that this reproduces only when master wal_level is hot_standby. > > I assume the problem isn't present if you set the primary to wal_level = > logical? Right. > > > > 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, By "start of decoding", I didn't get where exactly. Do you mean CheckLogicalDecodingRequirements() ? > and then raise an error > in decode.c when we pass an XLOG_PARAMETER_CHANGE record that sets > wal_level to something lower? Didn't get where exactly we should error out. We don't do XLOG_PARAMETER_CHANGE handling in decode.c , so obviously you meant something else, which I didn't understand. What I am thinking is : In CheckLogicalDecodingRequirements(), besides checking wal_level, also check ControlFile->wal_level when InHotStandby. I mean, when we are InHotStandby, both wal_level and ControlFile->wal_level should be >= WAL_LEVEL_LOGICAL. This will allow us to error out when using logical slot when master has incompatible wal_level. ControlFile is not accessible outside xlog.c so need to have an API to extract this field. > > Could you try to implement that? > > Greetings, > > Andres Freund -- Thanks, -Amit Khandekar EnterpriseDB Corporation The Postgres Database Company
