[Pgpool-hackers] Patch to avoid crashes after adding new node in Master/Slave mode

[Tatsuo Ishii]

Thanks for analyzing the problem and patches.

>     The ability to add new slave nodes, without requiring a restart was
> added in commit [1].
> 
>     One problem that was overlooked was that in main(), when initializing
> my_backend_status[], only NUM_BACKENDS number of elements of that array are
> initialized and used for the rest of the life of the pool_worker_child
> process. Since the NUM_BACKEDS increases everytime a new slave backend is
> added, but the corresponding element in the private array is still NULL, the
> pool_worker_child crashes when trying to check VALID_BACKEND(i) in
> establish_persistent_connection().
> 
>     The attached micro patch avoids the crashes by initializing the private
> array's all MAX_NUM_BACKENDS instead of just NUM_BACKENDS.
> 
>     This will also avoid crashes of pcp_attach_node when it tries to check
> VALID_BACKEND() in send_failback_request(). It crashes because, same as
> above, its private array is initialized only up to NUM_BACKENDS and the ID
> of the new slave node being attached is greater than current NUM_BACKENDS.
> 
>     The bigger concern, which this patch does not address, is that of
> keeping my_backend_status[] up-to-date in pool_worker_child process and any
> other auxiliary processes.

Ok. For this I will add a flag on shared memory area which is set by
main process. pool_worker_child process and other auxiliary processes
(curretly it's only pcp process) will check the flag and restart
itself if the flag is set.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
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