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 PGXCbool 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: { //createtable#ifdef PGXCCreateCommand((CreateStmt*)parse_tree, query_string, params, is_top_level, sent_to_remote, isCTAS);#elseCreateCommand((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，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
更多内容请参考：
https://docs.opengauss.org/zh/docs/3.1.0/docs/BriefTutorial/BriefTutorial.html
