[pgpool-hackers: 4541] 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.

Sorry, v2 patch is based on the v1 patch, not diff againt master
branch. Attached is the v3 patch against master branch.

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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