Re: Multi-Master Logical Replication

В Чт, 28/04/2022 в 09:49 +1000, Peter Smith пишет:

> 1.1 ADVANTAGES OF MMLR
>
> - Increases write scalability (e.g., all nodes can write arbitrary data).

I've never heard how transactional-aware multimaster increases
write scalability. More over, usually even non-transactional
multimaster doesn't increase write scalability. At the best it
doesn't decrease.

That is because all hosts have to write all changes anyway. But
side cost increases due to increased network interchange and
interlocking (for transaction-aware MM) and increased latency.

В Чт, 28/04/2022 в 08:34 +0000, kuroda(dot)hayato(at)fujitsu(dot)com пишет:
> Dear Laurenz,
>
> Thank you for your interest in our works!
>
> > I am missing a discussion how replication conflicts are handled to
> > prevent replication from breaking
>
> Actually we don't have plans for developing the feature that avoids conflict.
> We think that it should be done as core PUB/SUB feature, and
> this module will just use that.

If you really want to have some proper isolation levels (
Read Committed? Repeatable Read?) and/or want to have
same data on each "master", there is no easy way. If you
think it will be "easy", you are already wrong.

Our company has MultiMaster which is built on top of
logical replication. It is even partially open source
( https://github.com/postgrespro/mmts ) , although some
core patches that have to be done for are not up to
date.

And it is second iteration of MM. First iteration were
not "simple" or "easy" already. But even that version had
the hidden bug: rare but accumulating data difference
between nodes. Attempt to fix this bug led to almost
full rewrite of multi-master.

(Disclaimer: I had no relation to both MM versions,
I just work in the same firm).

regards

---------

Yura Sokolov