[pgpool-hackers: 3157] New feature proposal: Don't load balance after a SELECT having functions specified in black function list and queries specified in black_query_pattern_list

[Bo Peng]

Here is a proposal for Pgpool-II 4.1.

- Current feature of load balance

If we set "disable_load_balance_on_write = transaction",
when a write query is issued inside an explicit truncation, 
subsequent queries should be sent to primary only until the 
end of this transactionin in order to avoid the replication 
delay.

Example:
----------------------------------------
SELECT 1;     -- Load balanced.
BEGIN;
  UPDATE ...
  SELECT 1;   -- Don't be load balanced.
END;
SELECT 1;     -- Load balanced.
----------------------------------------

However, in the following cases they are not regarded as a write query 
and the subsequent read queries are still load balanced:
1. the SELECT having write functions specified in black_function_list
2. the queries specified in black_query_pattern_list


- Proposal

I think we should change this feature to regard 
the SELECT having write functions specified in black_function_list and 
the queries specified in black_query_pattern_list
as write queries.


To implement of this feature the following should be considered:

1. For backward compatibility, it's better to add a new parameter to enable this feature.
2. The queries regarded as write queries should not be cached.

What do you think?

-- 
Bo Peng <pengbo at sraoss.co.jp>
SRA OSS, Inc. Japan