ProcessUtilitySlow主要用于处理event triggers支持的语句，所以执行真正处理函数之前都需要执行event triggers支持相关的调用。如果传入参数不为PROCESS_UTILITY_SUBCOMMAND，就需要执行event triggers支持相关的调用。

static void ProcessUtilitySlow(ParseState *pstate,  PlannedStmt *pstmt, const char *queryString, ProcessUtilityContext context,
           ParamListInfo params, QueryEnvironment *queryEnv,  DestReceiver *dest, char *completionTag) {
  Node     *parsetree = pstmt->utilityStmt;
  bool    isTopLevel = (context == PROCESS_UTILITY_TOPLEVEL);
  bool    isCompleteQuery = (context != PROCESS_UTILITY_SUBCOMMAND);
  bool    needCleanup;
  bool    commandCollected = false;
  ObjectAddress address;
  ObjectAddress secondaryObject = InvalidObjectAddress;

  /* All event trigger calls are done only when isCompleteQuery is true */
  needCleanup = isCompleteQuery && EventTriggerBeginCompleteQuery();

  /* PG_TRY block is to ensure we call EventTriggerEndCompleteQuery */
  PG_TRY();
  {
    if (isCompleteQuery) EventTriggerDDLCommandStart(parsetree);
       switch (nodeTag(parsetree))
       ...
    /* Remember the object so that ddl_command_end event triggers have access to it. */
    if (!commandCollected) EventTriggerCollectSimpleCommand(address, secondaryObject, parsetree);

    if (isCompleteQuery) {
      EventTriggerSQLDrop(parsetree);
      EventTriggerDDLCommandEnd(parsetree);
    }
  }
  PG_CATCH();
  {
    if (needCleanup) EventTriggerEndCompleteQuery();
    PG_RE_THROW();
  }
  PG_END_TRY();

  if (needCleanup)
    EventTriggerEndCompleteQuery();
}

event triggers支持相关的调用流程如下所示，后续博客讲解。

EventTriggerBeginCompleteQuery
EventTriggerDDLCommandStart
EventTriggerSQLDrop
EventTriggerDDLCommandEnd
EventTriggerEndCompleteQuery

真正处理的情况

T_CreateSchemaStmt
T_CreateStmt
T_CreateForeignTableStmt
T_AlterTableStmt
T_AlterDomainStmt
T_DefineStmt
T_IndexStmt
T_CreateExtensionStmt
T_AlterExtensionStmt
T_AlterExtensionContentsStmt
T_CreateFdwStmt
T_AlterFdwStmt
T_CreateForeignServerStmt
T_AlterForeignServerStmt
T_CreateUserMappingStmt
T_AlterUserMappingStmt
T_DropUserMappingStmt
T_ImportForeignSchemaStmt
T_CompositeTypeStmt
T_CreateEnumStmt
T_CreateRangeStmt
T_AlterEnumStmt: /* ALTER TYPE (enum) /
T_ViewStmt: / CREATE VIEW /
T_CreateFunctionStmt / CREATE FUNCTION /
T_AlterFunctionStmt / ALTER FUNCTION /
T_RuleStmt / CREATE RULE /
T_CreateSeqStmt
T_AlterSeqStmt
T_CreateTableAsStmt
T_RefreshMatViewStmt
T_CreateTrigStmt
T_CreatePLangStmt
T_CreateDomainStmt
T_CreateConversionStmt
T_CreateCastStmt
T_CreateOpClassStmt
T_CreateOpFamilyStmt
T_CreateTransformStmt
T_AlterOpFamilyStmt
T_AlterTSDictionaryStmt
T_AlterTSConfigurationStmt
T_AlterTableMoveAllStmt
T_DropStmt:
T_RenameStmt
T_AlterObjectDependsStmt
T_AlterObjectSchemaStmt
T_AlterOwnerStmt
T_AlterOperatorStmt
T_CommentStmt
T_GrantStmt
T_DropOwnedStmt
T_AlterDefaultPrivilegesStmt
T_CreatePolicyStmt / CREATE POLICY /
T_AlterPolicyStmt / ALTER POLICY */
T_SecLabelStmt
T_CreateAmStmt
T_CreatePublicationStmt
T_AlterPublicationStmt
T_CreateSubscriptionStmt
T_AlterSubscriptionStmt
T_DropSubscriptionStmt
T_CreateStatsStmt
T_AlterCollationStmt