[pgpool-hackers: 4540] Re: New feature: log_backend_messages

[Tatsuo Ishii]

>>> Hi Peng,
>>> 
>>> Thank you for the feedback.
>>> 
>>>> Hi Ishii-san,
>>>> 
>>>> Thank you for your proposal.
>>>> I think it is a useful feature for debugging.
>>>> 
>>>>> One thing maybe better to think about the feature is, whether we want to show the log line:
>>>>> 2024-11-25 13:50:43.735: pgproto pid 325721: LOG:  DataRow message from backend 0
>>>> 
>>>> Yes, I agree with you to log messages using the message instead of the message kind.
>>> 
>>> Ok, attached is the patch to implement it.  The log messages look like
>>> below.
>>> 
>>> One thing I am wondering is, when a particular message is repeating,
>>> pgpool will not print the log immediately, just keep the number of
>>> messages while the same message type keeps on arriving. Once a
>>> different message type arrives, pgpool prints like:
>>> 
>>> 2024-11-27 17:08:35.245: pgproto pid 487733: LOG: last ParameterStatus message from backend 0 repeated 13 times
>>> 
>>> But what if the pgpool session terminates before the next different
>>> message arrives? pgpool print nothing. Thought?
>> 
>> After thinking more, maybe this is not a practical issue because
>> DataRow messages are always followed by CommandComplete or
>> ErrorResponse. Same thing can be said to ParameterStatus
>> messages. They are follwed by BackendKeyData or ErrorResponse. Also
>> this is applied to CopyData. The only case these are broken is, the
>> child process is killed while counting the number of messages.  Maybe
>> we could make log_backend_messages to take not only just on or off,
>> but something like:
>> 
>> off: the default
>> terse: current patch behavior (e.g. "last DataRow message from backend 0 repeated 7 times")
>> verbose: log each message as soon as it is detected. This never miss
>> 	 log messages even when the child process is killed, but could produce lots of log lines.
> 
> If we go the direction, we should allow to change the
> log_backend_messages value using "pgpool set" command to make
> testing/debugging easier: i.e. we set the value to terse or off in
> normal circumstance, once we need to testing/debugging we run "pgpool
> set log_backend_messages to verbose".

Attached is the v2 patch including documents and tests. Note that I
use the option name "none" to disable the feature instead of "off"
since "off" is tend to be used with "on" but log_backend_messages does
not "on" option. Thus I feel using solely "off" to be unnatural.

I believe the v2 patch is close to commit-able form.

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