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From: Alex <cdalxndr@yahoo.com>
Subject: Re: 15x slower PreparedStatement vs raw query
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: pgsql-performance@postgresql.org
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Shouldn't this process be automatic based on some heuristics?
Saving 10ms planning but costing 14s execution is catastrophic.
For example, using some statistics to limit planner time to some percent of 
of previous executions. 
This way, if query is fast, planning is fast, but if query is slow, more 
planning can save huge execution time.
This is a better general usage option and should be enabled by default, and 
users who want fast planning should set the variable to use the generic 
plan.
Justin Pryzby wrote:
On Sun, May 02, 2021 at 07:45:26PM +0000, Alex wrote:
PreparedStatement: 15s
Raw query with embedded params: 1s
See issue on github with query and explain analyze:
https://github.com/pgjdbc/pgjdbc/issues/2145 
<https://github.com/pgjdbc/pgjdbc/issues/2145> 
| ..PostgreSQL Version? 12
|Prepared statement
|...
|Planning Time: 11.596 ms
|Execution Time: 14799.266 ms
|
|Raw statement
|Planning Time: 22.685 ms
|Execution Time: 1012.992 ms
The prepared statemnt has 2x faster planning time, which is what it's meant 
to
improve.
The execution time is slower, and I think you can improve it with this.
https://www.postgresql.org/docs/12/runtime-config-query.html#GUC-PLAN-CACHE_MODE 
<https://www.postgresql.org/docs/12/runtime-config-query.html#GUC-PLAN-CACHE_MODE> 

|plan_cache_mode (enum)
| Prepared statements (either explicitly prepared or implicitly generated, 
for example by PL/pgSQL) can be executed using custom or generic plans. 
Custom plans are made afresh for each execution using its specific set of 
parameter values, while generic plans do not rely on the parameter values 
and can be re-used across executions. Thus, use of a generic plan saves 
planning time, but if the ideal plan depends strongly on the parameter 
values then a generic plan may be inefficient. The choice between these 
options is normally made automatically, but it can be overridden with 
plan_cache_mode. The allowed values are auto (the default), 
force_custom_plan and force_generic_plan. This setting is considered when a 
cached plan is to be executed, not when it is prepared. For more 
information see PREPARE.
-- 
Justin

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         <div id="compose-body-wrapper" dir="auto"><div 
dir="auto">Shouldn't this process be automatic based on some 
heuristics?</div><div dir="auto"><br></div><div dir="auto"> </div><div 
dir="auto">Saving 10ms planning but costing 14s execution is 
catastrophic.</div><div dir="auto"><br></div><div dir="auto">For example, 
using some statistics to limit planner time to some percent of of previous 
executions.&nbsp;</div><div dir="auto">This way, if query is fast, planning 
is fast, but if query is slow, more planning can save huge execution 
time.</div><div dir="auto">This is a better general usage option and should 
be enabled by default, and users who want fast planning should set the 
variable to use the generic plan.</div><div dir="auto" 
id="tmjah_g_1299"><p><br></p></div><br></div><div class="replyHeader" 
dir="auto">Justin Pryzby wrote:</div><br><br><div><blockquote 
cite="mid:20210503201811.GA27406@telsasoft.com" type="cite" style="margin:0 
0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>On Sun, May 02, 
2021 at 07:45:26PM +0000, Alex wrote:</div><br><blockquote 
class="gmail_quote" type="cite" style="margin:0 0 0 .8ex;border-left:1px 
#ccc solid;padding-left:1ex"><div> PreparedStatement: 15s</div><div> Raw 
query with embedded params: 1s</div><div> See issue on github with query 
and explain analyze:</div><br></blockquote><div> <a 
href="https://github.com/pgjdbc/pgjdbc/issues/2145">https://github.com/pgjdbc/pgjdbc/issues/2145</a></div><div><br></div><div>| 
..PostgreSQL Version?&nbsp; 12</div><div>|Prepared 
statement</div><div>|...</div><div>|Planning Time: 11.596 
ms</div><div>|Execution Time: 14799.266 ms</div><div>|</div><div>|Raw 
statement</div><div>|Planning Time: 22.685 ms</div><div>|Execution Time: 
1012.992 ms</div><div><br></div><div>The prepared statemnt has 2x faster 
planning time, which is what it's meant 
to</div><div>improve.</div><div><br></div><div>The execution time is 
slower, and I think you can improve it with this.</div><div><a 
href="https://www.postgresql.org/docs/12/runtime-config-query.html#GUC-PLAN-CACHE_MODE">https://www.postgresql.org/docs/12/runtime-config-query.html#GUC-PLAN-CACHE_MODE</a></div><div>|plan_cache_mode 
(enum)</div><div>|&nbsp; &nbsp; Prepared statements (either explicitly 
prepared or implicitly generated, for example by PL/pgSQL) can be executed 
using custom or generic plans. Custom plans are made afresh for each 
execution using its specific set of parameter values, while generic plans 
do not rely on the parameter values and can be re-used across executions. 
Thus, use of a generic plan saves planning time, but if the ideal plan 
depends strongly on the parameter values then a generic plan may be 
inefficient. The choice between these options is normally made 
automatically, but it can be overridden with plan_cache_mode. The allowed 
values are auto (the default), force_custom_plan and force_generic_plan. 
This setting is considered when a cached plan is to be executed, not when 
it is prepared. For more information see 
PREPARE.</div><div><br></div><div>-- 
</div><div>Justin</div></blockquote></div>
       
     
   
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