[pgpool-hackers: 1787] Problem with locking in In Memory Cache

[Huong Dangminh]

Hi, 

I have found a problem with table locking In In Memory Cache feature.
Confirmed in pgpool-II 3.4.8 in both memcached and sharedmemory mode.

When using JDBC to access to pgpool-II. In the second time of (the same) query 
executing, it returned result from cached, but after that pg_stat_activity's state of query 
was still in 'active' and not change. 
So the locks made by executed query was not release too.

Take a look at source and i found that, in extended protocol, locking of table 
was made when 'P'(Parse) message is sent, and release when 'S'(Sync) message
is sent to backend.
But when memory_cache_enabled is true. Parse message is sent but Sync message 
is not sent to backend.
In pool_fetch_from_memory_cache function. It sound that when cache found, 
Sync message from frontend was discard but not forward to backend to finish query.
I think, it is necessary to tell to backend to finish executed query here, is that right?

Best regards,
---
Dang Minh Huong
NEC Solution Innovators, Ltd.
http://www.nec-solutioninnovators.co.jp/en/