[pgpool-hackers: 3879] Proposal: If replication delay exceeds delay_threshold, elect a new load balance node with less delay

[KAWAMOTO Masaya]

Hi hackers.

On streaming replication mode, pgpool check the streaming delay on selected load
balance node if delay_threshold paraeter is larger than 0. When the delay exceeds
delay_theshold, pgpool send the query to primary regardless other standbies not
delayed. I want the user to be able to choose whether pgpool always send to primary
when there are other standbys with less delay by adding a boolean parameter
"prefer_lower_delay_standby" to pgpool.conf.

I improve select_load_balancing_node() function.
If "prefer_lower_delay" is true, pgpool selects another standby node that is lower delayed
than the suggested node even if the suggested node name matches
database_redirect_preference_list or app_redirect_preference_list.

Best Regards.

-- 
KAWAMOTO Masaya <kawamoto ¡÷ sraoss.co.jp>
SRA OSS, Inc. Japan
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