[pgpool-hackers: 3906] Re: Proposal: If replication delay exceeds delay_threshold, elect a new load balance node with less delay

[Tatsuo Ishii]

> Hi Peng.
> 
> I modified my patch.
> 
> The select_lower_delay_load_balance_node.patch_r3 includes documentation update.

It seems you coding sytle is against our standard. We inherit the
coding style of PostgreSQL:
https://www.postgresql.org/docs/13/source-format.html

> The test.sh is the regression test script.
> Please create directory src/test/regression/tests/033.prefer_lower_delay_standby and
> save it in that directory.

Why do you have the test.sh as a separate file? You could include a
new file like this:

$ git add -N test.sh
$ git diff HEAD

> On Tue, 11 May 2021 13:43:09 +0900
> KAWAMOTO Masaya <kawamoto at sraoss.co.jp> wrote:
> 
>> Hi,
>> 
>> Thank you for the feedback. 
>> 
>> >1. 2. 3.
>> 
>> Ok, I'll fix.
>> 
>> > 4. I want to confirm the feature.
>> >    According the follwoing code, it seems that if the replication_delay exceeds delay_threshold, 
>> >    you are electing the new load balancing node which has less delay than pool_config->delay_threshold.
>> >    The new load balancing load should be the backend with the least delay, isn't it?
>> 
>> I think that there is no problem because users allow the delay which set to delay_threshold.
>> But your idea seems to be better. I'll change to check all backends delay and select
>> the one with the least delay.
>> 
>> 
>> 
>> On Tue, 27 Apr 2021 00:16:41 +0900
>> Bo Peng <pengbo at sraoss.co.jp> wrote:
>> 
>> > Hi,
>> > 
>> > Thank you for your patch.
>> > I have reviewed your patch and below is the feedback.
>> > 
>> > 1. Pgpool-II follows the PostgreSQL coding conventions. 
>> > For example, the following code
>> > 
>> >   -                       pool_set_node_to_be_sent(query_context, PRIMARY_NODE_ID);
>> >   +                       if (prefer_lower_delay_standby){
>> >   +                           session_context->load_balance_node_id = select_load_balancing_node();
>> >   +                           pool_set_node_to_be_sent(query_context, session_context->load_balance_node_id);
>> >   +                       } else {
>> >   +                           pool_set_node_to_be_sent(query_context, PRIMARY_NODE_ID);
>> >   +                       }
>> > 
>> > should be in the following style:
>> > 
>> >   if (prefer_lower_delay_standby)
>> >   {
>> >       session_context->load_balance_node_id = select_load_balancing_node();
>> >       pool_set_node_to_be_sent(query_context, session_context->load_balance_node_id);
>> >   } 
>> >   else 
>> >   {
>> >       pool_set_node_to_be_sent(query_context, PRIMARY_NODE_ID);
>> >   }
>> > 
>> > 2. The patch should include a regression test which is used to test the new feature.
>> > 
>> > 3. The patch should include documentation update.
>> > 
>> > 4. I want to confirm the feature.
>> >    According the follwoing code, it seems that if the replication_delay exceeds delay_threshold, 
>> >    you are electing the new load balancing node which has less delay than pool_config->delay_threshold.
>> >    The new load balancing load should be the backend with the least delay, isn't it?
>> >  
>> >   +				if ( VALID_BACKEND(i) &&
>> >   +					 !IS_PRIMARY_NODE_ID(i) &&
>> >   +				 	(bkinfo->standby_delay < pool_config->delay_threshold) &&
>> >   +				 	bkinfo->backend_weight > 0 )
>> >   +				{
>> >   +					selected_slot = i;
>> >   +					break;
>> >   +				}
>> > 
>> > 
>> > On Tue, 20 Apr 2021 17:24:35 +0900
>> > KAWAMOTO Masaya <kawamoto at sraoss.co.jp> wrote:
>> > 
>> > > 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 at sraoss.co.jp>
>> > > SRA OSS, Inc. Japan
>> > 
>> > 
>> > -- 
>> > Bo Peng <pengbo at sraoss.co.jp>
>> > SRA OSS, Inc. Japan
>> 
>> 
>> -- 
>> KAWAMOTO Masaya <kawamoto at sraoss.co.jp>
>> SRA OSS, Inc. Japan
>> _______________________________________________
>> pgpool-hackers mailing list
>> pgpool-hackers at pgpool.net
>> http://www.pgpool.net/mailman/listinfo/pgpool-hackers
> 
> 
> -- 
> KAWAMOTO Masaya <kawamoto at sraoss.co.jp>
> SRA OSS, Inc. Japan