[pgpool-hackers: 4090] What to do with ParamterStatus?

[Tatsuo Ishii]

Currently Pgpool-II only processes ParameterStatus messages at the
connection starting up phase. In the phase all ParameterStatus
messages from the primary node are forwarded to frontend. If value for
a ParameterStatus is differ among backends, only the value of primary
node is forwarded and the value of standby nodes are ignored.  In this
case it is logged that the message lenth (thus values) are differ
(except is_hot_standby, which is always differ among primary and
standby). So far so good.

Question is, in the case ParameterStatus message arrives after
establishing the session. This could happen in certain cases. For
example, postgresql.conf is changed and reloaded. The other case is,
SET command is rolled back. Currently Pgpool-II ignores
ParameterStatus messages in these cases.

I think this is not good because frontend never knows the value of
parameters have been changed. So what should we do?

1) Every time ParameterStatus message is received, forward it to
frontend. Even the value for standby servers are forwarded. This may
result in receiving multiple ParameterStatus for frontend if user
changes postgresql.conf and reloads it on each server.

2) Process ParameterStatus only when the message is received from the
primary server.

3) Other.

I think #2 is reasonable because it is consistent with the process
done at the starting up.

Comments/Suggestions?

Best reagards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp