Hi,
I looked some comment for the synchronous replication and understood
the consensus of the community was that the sync replication should be
added using not hooks and plug-ins but core-patches. If my understanding
is right, I will change my development plan so that the sync replication
may be put into core.
But, I don't think every features should be put into core. Of course, the
high-availability features (like clustering, automatic failover, ...etc) are
out of postgres. The user who wants whole HA solution using the sync
replication must integrate postgres and clustering software like heartbeat.
WAL sending should be put into core. But, I'd like to separate WAL
receiving from core and provide it as a new contrib tool. Because,
there are some users who use the sync replication as only WAL
streaming. They don't want to start postgres on the slave. Of course,
the slave can replay WAL by using pg_standby and WAL receiver tool
which I'd like to provide as a new contrib tool. I think the patch against
recovery code is not necessary.
I arrange the development items below :
1) Patch around XLogWrite.
It enables a backend to wake up the WAL sender process at the
timing of COMMIT.
2) Patch for the communication between a backend and WAL
sender process.
There were some discussions about this topic. Now, I decided to
adopt imessages proposed by Markus.
3) Patch of introducing new background process which I've called
WALSender. It takes charge of sending WAL to the slave.
Now, I assume that WALSender also listens the connection from
the slave, i.e. only one sender process manages multiple slaves.
The relation between WALSender and backend is 1:1. So,
the communication mechanism between them can be simple.
As other idea, I can introduce new listener process and fork new
WALSender for every slave. Which architecture is better? Or,
should postmaster listen also the connection from the slave?
4) New contrib tool which I've called WALReceiver. It takes charge
of receiving WAL from the master and writing it to disk on the slave.
I will submit these patches and tool by Nov Commit Fest at the latest.
Any comment welcome!
best regards
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
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