openGauss内核分析：数据库表的创建过程

除了DML之外的所有查询都通过ProcessUtility模块来执行，包括了各类DDL语句、事务相关语句、游标相关语句等。上层调用函数为exec_simple_query函数，其中PortalStart函数和PortalDrop函数部分较为简单。核心函数是PortalRun函数下层调用的standard_ProcessUtility函数，该函数通过switch case语句处理了各种类型的查询语句，包括事务相关查询、游标相关查询、schema相关操作、表空间相关操作、表定义相关操作等。

standard_ProcessUtility函数会根据nodeTag(parsetree)的值来确定sql的操作类型，create table一般都是进入T_CreateStmt分支，调用CreateCommand函数。

void?standard_ProcessUtility(Node*?parse_tree,?const?char*?query_string,?ParamListInfo?params,?bool?is_top_level,????DestReceiver*?dest,#ifdef?PGXC????bool?sent_to_remote,#endif?/*?PGXC?*/????char*?completion_tag,????bool?isCTAS){……????errno_t?errorno?=?EOK;switch?(nodeTag(parse_tree))?{?//?根据nodeTag(parsetree)的值来确定sql的操作类型……????????case?T_CreateStmt:?{?//?create?table#ifdef?PGXC????????????CreateCommand((CreateStmt*)parse_tree,?query_string,?params,?is_top_level,?sent_to_remote,?isCTAS);#else????????????CreateCommand((CreateStmt*)parse_tree,?query_string,?params,?is_top_level,?isCTAS);#endif????????}?break;……

CreateCommand函数先解析parse_tree获取stmt，如果stmt为空则表明表已经存在。如果stmt不为空对stmts进行遍历，如果是 CreateStmt就调用DefineRelation。AlterTableCreateToastTable判断是否需要创建toast表并创建创建数据库表，AlterCStoreCreateTables判断是否需要创建列存表并创建。

#ifdef?PGXCvoid?CreateCommand(CreateStmt?*parse_tree,?const?char?*query_string,?ParamListInfo?params,???????????????????bool?is_top_level,?bool?sent_to_remote,?bool?isCTAS)#elsevoid?CreateCommand(CreateStmt?*parse_tree,?const?char?*query_string,?ParamListInfo?params,?bool?is_top_level,????bool?isCTAS)#endif{……????/*?Run?parse?analysis?...?*/????if?(u_sess->attr.attr_sql.enable_parallel_ddl)?//?先解析parse_tree获取stmt????????stmts?=?transformCreateStmt((CreateStmt*)parse_tree,?query_string,?NIL,?true,?&namespace_id,?is_first_node);????else????????stmts?=?transformCreateStmt((CreateStmt*)parse_tree,?query_string,?NIL,?false,?&namespace_id);
????/*?????*?If?stmts?is?NULL,?then?the?table?is?exists.?????*?we?need?record?that?for?searching?the?group?of?table.?????*/????if?(stmts?==?NIL)?{?//?如果stmt为空则表明表已经存在????????table_is_exist?=?true;……????/*?...?and?do?it?*/????foreach?(l,?stmts)?{?//?遍历stmts        Node* stmt = (Node*)lfirst(l);
????????if?(IsA(stmt,?CreateStmt))?{??//?如果是?CreateStmt就调用DefineRelation????????????Datum?toast_options;            static const char* const validnsps[] = HEAP_RELOPT_NAMESPACES;???????????????????????/*?forbid?user?to?set?or?change?inner?options?*/            ForbidOutUsersToSetInnerOptions(((CreateStmt*)stmt)->options);????????????????????????/*?Create?the?table?itself?*/????????????rel_oid?=?DefineRelation((CreateStmt*)stmt,????????????????????????????????????((CreateStmt*)stmt)->relkind?==?RELKIND_MATVIEW??????????????????????????????????????????????????????????????????????RELKIND_MATVIEW : RELKIND_RELATION,????????????????????????????????????????????????????????????????????????????????????????????????????????InvalidOid,?isCTAS);……????????????AlterTableCreateToastTable(rel_oid,?toast_options,?AccessShareLock);????????????AlterCStoreCreateTables(rel_oid,?toast_options,?(CreateStmt*)stmt);????????????AlterDfsCreateTables(rel_oid,?toast_options,?(CreateStmt*)stmt);????????????AlterCreateChainTables(rel_oid,?toast_options,?(CreateStmt?*)stmt);……

DefineRelation函数获取到表名relname、名字空间relnamespace、表空间reltablespace、表类型relkind和relpersistence等信息后调用heap_create_with_catalog创建relation。

(gdb)?f?0#0??heap_create_with_catalog?(relname=0x7fb4fa872140?"t100",?relnamespace=2200,?reltablespace=0,?relid=0,?reltypeid=0,????reloftypeid=0,?ownerid=10,?tupdesc=0x7fb4ff2e2e50,?cooked_constraints=0x0,?relkind=114?'r',?relpersistence=112?'p',????shared_relation=false,?mapped_relation=false,?oidislocal=false,?oidinhcount=0,?oncommit=ONCOMMIT_NOOP,????reloptions=140415352057720,?use_user_acl=true,?allow_system_table_mods=false,?partTableState=0x0,?row_compress=1?'\001',    bucketinfo=0x0, record_dependce=true, ceLst=0x0, storage_type=HEAP_DISK, partLockMode=1) at heap.cpp:2521

其中heap_create内部首先调用了RelationBuildLocalRelation创建RelationData，并加入到relCache，RelationData表示一个表的元信息，这些信息都可以由系统表元组中的信息构造得到。然后根据这些信息通过调用RelalionCreateStorage函数创建物理文件。heap_create_with_catalog主要完成表物理文件的创建和表元信息注册到系统表中，涉及系统包包括pg_class，pg_attribute，pg_depend，pg_object，pg_type，pg_index和pg_partition。

附：创建表create table的函数调用栈

#0??RelationCreateStorage#1??heap_create#2??heap_create_with_catalog#3??DefineRelation#4??CreateCommand#5??standard_ProcessUtility#6??gsaudit_ProcessUtility_hook#7??pgaudit_ProcessUtility#8??hypo_utility_hook#9??ProcessUtility#10?PortalRunUtility#11?PortalRunMulti#12?PortalRun#13?exec_simple_query#14 PostgresMain

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