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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 < $1;PREPAREpostgres=#
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 -------endIn 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(2); id ----1(1 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 -------endIn exec_simple_query loop for parsetree_list++++++++++++++++++++++++++After pg_plan_queries...In exec_simple_query....Before PortalRun.....In PortalRun ------------startxxxxxxIn 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 ------------endxxxxxxxxxxxIn ExecuteQuery--------end..........In standard_ProcessUtility ... After ExecuteQuery .........In ProcessUtility----End.......In PortalRunUtility ---------------endxxxxxxIn 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。
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/p/3144475.html，如需转载请自行联系原作者