Lock release leak in pool_search_relcache

While looking into src/utils/pool_relcache.c for other reasons, I
noticed pool_search_relcache does not release lock in a certain code
path. When the local relation cache does not hit, it searches the
shared relation cache if enable_shared_relcache is on. If the lock for
query cache has been already held (thus the variable "locked" is set
to true), it acquires a shared lock, then releases it and acquires an
exclusive lock to call pool_catalog_commit_cache. Since in this code
path variable "locked" is set to true, subsequent code:

if (pool_config->enable_shared_relcache && !locked)
{
pool_shmem_unlock();
POOL_SETMASK(&oldmask);
}

does not reach inside the if statement -- lock is not released. I
think to fix this, the following code requires "locked = false;"

pool_shmem_unlock();
pool_shmem_lock(POOL_MEMQ_EXCLUSIVE_LOCK);
pool_catalog_commit_cache(backend, query, query_cache_data, query_cache_len);

Attached patch does this. Plus following changes are made in the patch:

- the variable name "locked" is confusing. To clarify the role of the
variable, its name is changed to "locked_by_others".

- Fix per_node_statement_log is called even though actual query is
not sent to backend.

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