PostgreSQL的prepare 和 execute 动作背后

我给PostgreSQL的源代码加入了调试信息以后，会有如下表现：

我执行Prepare：

postgres=# prepare s(int) as select * from tst01 t where id < $;
PREPARE
postgres=# 

背后的反应：

** In PostgresMain
In exec_simple_query loop for parsetree_list++++++++++++++++++++++++++Before pg_plan_queries
***************In pg_plan_queries -------start
................In pg_plan_queries...query->commandType == CMD_UTILITY
***************In pg_plan_queries -------end
In exec_simple_query loop for parsetree_list++++++++++++++++++++++++++After pg_plan_queries

...In exec_simple_query....Before PortalRun
.....In PortalRun ------------start
.......In PortalRunUtility ---------------start
.........In ProcessUtility----Start
.........In ProcessUtility----End
.......In PortalRunUtility ---------------end
.....In PortalRun ------------end
...In exec_simple_query....After PortalRun

接着执行 Execute:

postgres=# execute s();
 id
----

( row)

postgres=# 

背后的反应：

In exec_simple_query loop for parsetree_list++++++++++++++++++++++++++Before pg_plan_queries
***************In pg_plan_queries -------start
................In pg_plan_queries...query->commandType == CMD_UTILITY
***************In pg_plan_queries -------end
In exec_simple_query loop for parsetree_list++++++++++++++++++++++++++After pg_plan_queries

...In exec_simple_query....Before PortalRun
.....In PortalRun ------------start
xxxxxxIn FillPortalStore ...........start
.......In PortalRunUtility ---------------start
.........In ProcessUtility----Start
..........In standard_ProcessUtility ... Before ExecuteQuery
xxxxxxxxxxxIn ExecuteQuery--------start
++++++++++++In GetCachedPlan ........start
.............In BuildCachedPlan, Before pg_plan_queries
***************In pg_plan_queries -------start
................In pg_plan_queries...query->commandType != CMD_UTILITY
..................In pg_plan_query........start
*******************In planner ........start
___________________In standard_planner........start
********************In subquery_planner........start
++++++++++++++++++++++In grouping_planner......start
************************In query_planner......start
........................In make_one_rel......start
...........................In set_base_rel_pathlists......start
-----------------------------In set_rel_pathlist......start
******************************In set_plain_rel_pathlist......start
-------------------------------Before add_path of seqscan
-------------------------------After add_path of seqscan

-------------------------------Before create_index_paths
-------------------------------After create_index_path

-------------------------------Before create_tidscan_paths
-------------------------------After create_tidscan_paths

-------------------------------Before set_cheapest
-------------------------------After set_cheapest

******************************In set_plain_rel_pathlist......end
-----------------------------In set_rel_pathlist......end
...........................In set_base_rel_pathlists......end
........................In make_one_rel......end
************************In query_planner......end
++++++++++++++++++++++In grouping_planner......end
********************In subquery_planner........end
___________________In standard_planner........end
*******************In planner ........end
..................In pg_plan_query........end
***************In pg_plan_queries -------end
.............In BuildCachedPlan, After pg_plan_queries
++++++++++++In GetCachedPlan ........end

.....In PortalRun ------------start
.....In PortalRun ------------end
xxxxxxxxxxxIn ExecuteQuery--------end
..........In standard_ProcessUtility ... After ExecuteQuery
.........In ProcessUtility----End
.......In PortalRunUtility ---------------end
xxxxxxIn FillPortalStore ...........end
.....In PortalRun ------------end
...In exec_simple_query....After PortalRun

按照对过去版本的认识，应当是PortalRun的时候单纯执行计划。

但是preapre....execute 方式，把它破坏了。

可以看到，prepare时候，不进行path的生成。

execute 的时候，在PortalRun的阶段，通过 ExecuteQuery->GetCachedPlan->BuildCachedPlan，

来生成path和确定plan。

不过要注意到一点是，我所执行的上述的例子中，并没有导致 param_info 非空。

可以说，这种针对单一表的preapre execute，是把执行计划的生成推后了，但是并不等于它就是 Parameterized Path。