On 2020/06/02 13:24, Michael Paquier wrote:
On Fri, May 29, 2020 at 06:09:06PM +0900, Masahiko Sawada wrote:
Yes. Conversely, if we start logical replication in a physical
replication connection (i.g. replication=true) we got an error before
staring replication:
ERROR: logical decoding requires a database connection
I think we can prevent that SEGV in a similar way.
Still unconvinced as this restriction stands for logical decoding
requiring a database connection but it is not necessarily true now as
physical replication has less restrictions than a logical one.
Could you tell me what the benefit for supporting physical replication on
logical rep connection is? If it's only for "undocumented"
backward-compatibility, IMO it's better to reject such "tricky" set up.
But if there are some use cases for that, I'm ok to support that.
Looking at the code, I think that there is some confusion with the
fake WAL reader used as base reference in InitWalSender() where we
assume that it could only be used in the context of a non-database WAL
sender. However, this initialization happens when the WAL sender
connection is initialized, and what I think this misses is that we
should try to initialize a WAL reader when actually going through a
START_REPLICATION command.
I can note as well that StartLogicalReplication() moves in this sense
by setting xlogreader to be the one from logical_decoding_ctx once the
decoding context has been created.
This results in the attached. The extra test from upthread to check
that logical decoding is not allowed in a non-database WAL sender is a
good idea, so I have kept it.
Yes. Also we should add the test to check if physical replication can work
fine even on logical rep connection?
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
