pglogical: Segmentation fault when using last_update_wins

Hi,

This is a cross-post of this issue
<https://github.com/2ndQuadrant/pglogical/issues/31> on pglogical's github
site. There doesn't seem to be much activity on that site so I'm trying my
luck here.

I'd like to know if using pglogical to do multi-master replication is sane. The
docs <https://2ndquadrant.com/en/resources/pglogical/> say that it is not
supported: "pglogical does not provide multi-master replication". If so
then this is probably not a bug.

I'm experimenting with a 2-node bidirectional replication using pglogical
1.1.2 and PostgreSQL 9.5. I'm able to consistently cause a seg fault when I
set pglogical.conflict_resolution = 'last_update_wins', and when either:

- Executing simultaneous identical UPDATE statements on both nodes
(using psql and terminator) or
- Disabling both subscriptions, executing UPDATE statements on both
nodes (that will cause a conflict) and then re-enabling one or both
subscriptions.

More details can be found in the original post
<https://github.com/2ndQuadrant/pglogical/issues/31>. So far in my testing
this is the only issue I've encountered using pglogical to do multi-master
replication.

Using BDR would be ideal: I'm looking for async multi-master replication.
But using a patched PostgreSQL 9.4 is a show-stopper.

Should I just wait for a future version of PostgreSQL to have a better
integration with BDR?

Thank you,

...Jelle

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