[pgpool-hackers: 2271] Re: RFC: New health check implementation

[Tatsuo Ishii]

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

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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