[pgpool-hackers: 2276] Re: RFC: New health check implementation

[Tatsuo Ishii]

>> On 21-Apr-2017, at 4:31 AM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>> 
>> Usama,
>> 
>> Is it possible to have following config parameter at the same time?
>> My feeling is we can't because current implementation of config
>> handling does not allow it.
>> 
>> health_check_period = 10
>> health_check_period0 = 5
> 
> Yes, having the same named configuration parameter with and without index postfix would cause problem with the current implementations, but if we want to support this I can tweak the configuration framework to allow that.

That would be desirable.

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

> Thanks
> Best regards
> Muhammad Usama 
> 
>> 
>> Best regards,
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese:http://www.sraoss.co.jp
>> 
>>> Hi,
>>> 
>>> This is a Request for Comments on the new implementation of health
>>> check aiming for Pgpool-II 3.7.
>>> 
>>> Problems:
>>> 
>>> Current implementation of health check is a single serial processing
>>> for all of database nodes. This implies some limitations for health
>>> check process: 1) it is not possible to specify different health check
>>> configuration values for each database node, 2) node failure detection
>>> may take longer. For example, if it takes 10 seconds before detecting
>>> node 0 failure, then detecting node 1 failure will be delayed at least
>>> 10 seconds because it starts node failure detection after node 0.
>>> 
>>> The solution:
>>> 
>>> Allow to specify health check parameters for each node. Pgpool.conf
>>> will look like:
>>> 
>>> health_check_period0 = 10
>>> health_check_timeout0 = 20
>>> :
>>> :
>>> 
>>> where "0" means database node 0 (similar concept as "backend_*0
>>> parameters).
>>> 
>>> To make admin's life easier, current parameters can be used as
>>> well. Suppose there are 3 nodes, and we have:
>>> 
>>> health_check_period = 10
>>> health_check_period0 = 5
>>> 
>>> then health_check_period for node 1 and 2 will be 10, while
>>> health_check_period for node 0 will be 5. So parameter names without
>>> node id works as a "global variable".
>>> 
>>> The implementation:
>>> 
>>> Create separate child process of pgpool main process and let do the
>>> heal check job for each database node. Once the health check child
>>> process detects node failure, it signals to main process and main
>>> process will perform failover.
>>> 
>>> This architecture makes pgpool main process simpler and robust, while
>>> earlier detection of node failure by the health check child process.
>>> 
>>> Comments and suggestions are welcome.
>>> 
>>> Best regards,
>>> --
>>> Tatsuo Ishii
>>> SRA OSS, Inc. Japan
>>> English: http://www.sraoss.co.jp/index_en.php
>>> Japanese:http://www.sraoss.co.jp
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