postgresql SQL 的相关内容

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之十五

如此：接前面，看 add_base_rels_to_query函数： /* * add_base_rels_to_query * * Scan the query's jointree and create baserel RelOptInfos for all * the base relations (ie, table, subquery, and fun...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之十六

接着分析：build_simple_rel 函数 /* * build_simple_rel * Construct a new RelOptInfo for a base relation or 'other' relation. */ RelOptInfo * build_simple_rel(PlannerInfo *root, int relid, RelOptKin...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之十七

继续： /* * estimate_rel_size - estimate # pages and # tuples in a table or index * * We also estimate the fraction of the pages that are marked all-visible in * the visibility map, for use in est...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之十八

接前面，由于看到对 BasicOpenFile 函数的调用。自然想到，如果两个进程同时访问一个表(即同一文件)，会否有冲突或效率的问题。开两个psql客户端，连接数据库后，后台生成两个进程，分别运行 select * from tst01 进行观察...发现各进程之间互相不干扰。我实验的方法，加入调试代码： /* * BasicOpenFile --- same as open(...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十一

接前面: 回到mdopen上来，看看是谁调用了 mdopen，又获得了什么。 /* * mdnblocks() -- Get the number of blocks stored in a relation. * * Important side effect: all active segments of the relation are opened * ...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十六

接前面，再次上溯一个层次，看代码(planmain.c :query_planner)： void query_planner(PlannerInfo *root, List *tlist, double tuple_fraction, double limit_tuples, Path **cheapest_path, Path **...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十七

接前面，仔细看这个：这 add_base_rels_to_query 是个递归调用嘛。想像一下： select * from tst01 where id in (select sid from tst02) or id in (select sid from tst03) 之类的，此函数将层层深入，构造一个二叉树式样的语法树。 void add_base_...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之二十九

接前面，继续分析 ChoosePortalStrategy： /* * ChoosePortalStrategy * Select portal execution strategy given the intended statement list. * * The list elements can be Querys, PlannedStmts, or utili...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之三十一

回到上一个层面，继续看 PortalStart的处理： void PortalStart(Portal portal, ParamListInfo params, int eflags, bool use_active_snapshot) { ... PG_TRY(); { ... /* * ...

文章 2022-02-16 来自：开发者社区

PostgreSQL在何处处理 sql查询之三十二

接前面，继续观察 PortalStart，其中有： /* * Create QueryDesc in portal's context; for the moment, set * the destination to DestNone. */ ...

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