quorum commit Re: Synchronous replication

On Thu, Jul 22, 2010 at 5:37 PM, Yeb Havinga <yebhavinga@gmail.com> wrote:

Fujii Masao wrote:

How should the synchronous replication behave when the number of connected
standby servers is less than quorum?

1. Ignore quorum. The current patch adopts this. If the ACKs from all
  connected standbys have arrived, transaction commit is successful
  even if the number of standbys is less than quorum. If there is no
  connected standby, transaction commit always is successful without
  regard to quorum.

2. Observe quorum. Aidan wants this. Until the number of connected
  standbys has become more than or equal to quorum, transaction commit
  waits.

Which is the right behavior of quorum commit? Or we should add new
parameter specifying the behavior of quorum commit?

Initially I also expected the quorum to behave like described by
Aidan/option 2.

I have another question about the detailed design of quorum commit.

In the following case, how should quorum commit behave?

1. quorum_standbys = 2; there are three connected synchronous standbys
2. One standby sends the ACK back and fails
3. The ACK arrives from another standby
4. How should quorum commit behave?

(a) Transaction commit returns a "success" since the master has already
received two ACKs
(b) Transaction commit waits for the "last" ACK since only one of
currently connected standbys has sent the ACK

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center