我们分析一下外部数据包装器中创建外部服务器的CREATE SERVER命令的实现源码。前面已经分析过很多DDL的语法实现。这里简单描述一下大致过程。
主流程如下所示：
c
exec_simple_query(query_string);
--> pg_parse_query(query_string);
--> raw_parser(query_string, RAW_PARSE_DEFAULT);
--> base_yyparse(yyscanner);
--> pg_analyze_and_rewrite_fixedparams(parsetree, query_string, NULL, 0, NULL);
--> pg_plan_queries(querytree_list, query_string, CURSOR_OPT_PARALLEL_OK, NULL);
--> PortalStart(portal, NULL, 0, InvalidSnapshot);
--> PortalRun(portal, FETCH_ALL, true, true, receiver, receiver, &qc);
--> standard_ProcessUtility(pstmt, queryString, readOnlyTree,context, params, queryEnv, dest, qc);
--> CreateForeignServer((CreateForeignServerStmt *) parsetree);
--> table_open(ForeignServerRelationId, RowExclusiveLock);
--> get_foreign_server_oid(stmt->servername, true);
--> transformGenericOptions(ForeignServerRelationId, PointerGetDatum(NULL), stmt->options, fdw->fdwvalidator);
--> CatalogTupleInsert(rel, tuple);
--> table_close(rel, RowExclusiveLock);
--> PortalDrop(portal, false);语法解析层面
gram.y语法定义：
c
/*************************************************
*
* QUERY:
* CREATE SERVER name [TYPE] [VERSION] [OPTIONS]
*
***************************************************/
CreateForeignServerStmt: CREATE SERVER name opt_type opt_foreign_server_version
FOREIGN DATA_P WRAPPER name create_generic_options
{
CreateForeignServerStmt *n = makeNode(CreateForeignServerStmt);
n->servername = $3;
n->servertype = $4;
n->version = $5;
n->fdwname = $9;
n->options = $10;
n->if_not_exists = false;
$$ = (Node *) n;
}
| CREATE SERVER IF_P NOT EXISTS name opt_type opt_foreign_server_version
FOREIGN DATA_P WRAPPER name create_generic_options
{
CreateForeignServerStmt *n = makeNode(CreateForeignServerStmt);
n->servername = $6;
n->servertype = $7;
n->version = $8;
n->fdwname = $12;
n->options = $13;
n->if_not_exists = true;
$$ = (Node *) n;
}
;
opt_type:
TYPE_P Sconst { $$ = $2; }
| /*EMPTY*/ { $$ = NULL; }
;
foreign_server_version:
VERSION_P Sconst { $$ = $2; }
| VERSION_P NULL_P { $$ = NULL; }
;
opt_foreign_server_version:
foreign_server_version { $$ = $1; }
| /*EMPTY*/ { $$ = NULL; }
;create foreign server实现
下面是创建外部服务器的主要实现函数，核心就是向pg_foreign_server系统表中插入一条记录。
sql
postgres=# select * from pg_foreign_server ;
oid | srvname | srvowner | srvfdw | srvtype | srvversion | srvacl | srvoptions
-------+------------------+----------+--------+---------+------------+--------+--------------------------------------------------
16820 | s1 | 10 | 16811 | | | |
16825 | foreign_pgserver | 10 | 16815 | | | | {host=192.168.109.133,port=6432,dbname=postgres}
(2 rows)具体实现如下：
- 需要现在外部服务器命名唯一，不能与已有名重复
- 解析options
c
/* Create a foreign server */
ObjectAddress CreateForeignServer(CreateForeignServerStmt *stmt)
{
Relation rel;
Datum srvoptions;
Datum values[Natts_pg_foreign_server];
bool nulls[Natts_pg_foreign_server];
HeapTuple tuple;
Oid srvId;
Oid ownerId;
AclResult aclresult;
ObjectAddress myself;
ObjectAddress referenced;
ForeignDataWrapper *fdw;
rel = table_open(ForeignServerRelationId, RowExclusiveLock);
/* For now the owner cannot be specified on create. Use effective user ID. */
ownerId = GetUserId();
/* Check that there is no other foreign server by this name. If there is
* one, do nothing if IF NOT EXISTS was specified. */
srvId = get_foreign_server_oid(stmt->servername, true);
if (OidIsValid(srvId))
{
if (stmt->if_not_exists)
{
/* If we are in an extension script, insist that the pre-existing
* object be a member of the extension, to avoid security risks. */
ObjectAddressSet(myself, ForeignServerRelationId, srvId);
checkMembershipInCurrentExtension(&myself);
/* OK to skip */
ereport(NOTICE,
(errcode(ERRCODE_DUPLICATE_OBJECT),
errmsg("server \"%s\" already exists, skipping",stmt->servername)));
table_close(rel, RowExclusiveLock);
return InvalidObjectAddress;
}
else
ereport(ERROR,
(errcode(ERRCODE_DUPLICATE_OBJECT),
errmsg("server \"%s\" already exists",stmt->servername)));
}
/* Check that the FDW exists and that we have USAGE on it. Also get the
* actual FDW for option validation etc. */
fdw = GetForeignDataWrapperByName(stmt->fdwname, false);
aclresult = pg_foreign_data_wrapper_aclcheck(fdw->fdwid, ownerId, ACL_USAGE);
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, OBJECT_FDW, fdw->fdwname);
/* Insert tuple into pg_foreign_server. */
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
srvId = GetNewOidWithIndex(rel, ForeignServerOidIndexId, Anum_pg_foreign_server_oid);
values[Anum_pg_foreign_server_oid - 1] = ObjectIdGetDatum(srvId);
values[Anum_pg_foreign_server_srvname - 1] = DirectFunctionCall1(namein, CStringGetDatum(stmt->servername));
values[Anum_pg_foreign_server_srvowner - 1] = ObjectIdGetDatum(ownerId);
values[Anum_pg_foreign_server_srvfdw - 1] = ObjectIdGetDatum(fdw->fdwid);
/* Add server type if supplied */
if (stmt->servertype)
values[Anum_pg_foreign_server_srvtype - 1] = CStringGetTextDatum(stmt->servertype);
else
nulls[Anum_pg_foreign_server_srvtype - 1] = true;
/* Add server version if supplied */
if (stmt->version)
values[Anum_pg_foreign_server_srvversion - 1] = CStringGetTextDatum(stmt->version);
else
nulls[Anum_pg_foreign_server_srvversion - 1] = true;
/* Start with a blank acl */
nulls[Anum_pg_foreign_server_srvacl - 1] = true;
/* Add server options */
srvoptions = transformGenericOptions(ForeignServerRelationId, PointerGetDatum(NULL), stmt->options, fdw->fdwvalidator);
if (PointerIsValid(DatumGetPointer(srvoptions)))
values[Anum_pg_foreign_server_srvoptions - 1] = srvoptions;
else
nulls[Anum_pg_foreign_server_srvoptions - 1] = true;
tuple = heap_form_tuple(rel->rd_att, values, nulls);
CatalogTupleInsert(rel, tuple);
heap_freetuple(tuple);
/* record dependencies */
myself.classId = ForeignServerRelationId;
myself.objectId = srvId;
myself.objectSubId = 0;
referenced.classId = ForeignDataWrapperRelationId;
referenced.objectId = fdw->fdwid;
referenced.objectSubId = 0;
recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
recordDependencyOnOwner(ForeignServerRelationId, srvId, ownerId);
/* dependency on extension */
recordDependencyOnCurrentExtension(&myself, false);
/* Post creation hook for new foreign server */
InvokeObjectPostCreateHook(ForeignServerRelationId, srvId, 0);
table_close(rel, RowExclusiveLock);
return myself;
}drop server的流程
drop server主流程如下：
c
exec_simple_query(query_string);
--> pg_parse_query(query_string);
--> raw_parser(query_string, RAW_PARSE_DEFAULT);
--> base_yyparse(yyscanner);
--> pg_analyze_and_rewrite_fixedparams(parsetree, query_string, NULL, 0, NULL);
--> pg_plan_queries(querytree_list, query_string, CURSOR_OPT_PARALLEL_OK, NULL);
--> PortalStart(portal, NULL, 0, InvalidSnapshot);
--> PortalRun(portal, FETCH_ALL, true, true, receiver, receiver, &qc);
--> standard_ProcessUtility(pstmt, queryString, readOnlyTree,context, params, queryEnv, dest, qc);
--> ExecDropStmt((DropStmt *) parsetree, isTopLevel);
--> RemoveObjects(stmt);
--> get_object_address(stmt->removeType, object, &relation, AccessExclusiveLock, stmt->missing_ok);
--> get_object_address_unqualified(objtype, castNode(String, object), missing_ok);
--> performMultipleDeletions(objects, stmt->behavior, 0);
--> deleteObjectsInList(targetObjects, &depRel, flags);
--> deleteOneObject(thisobj, depRel, flags);
--> doDeletion(object, flags);
--> DropObjectById(object);
--> PortalDrop(portal, false);语法定义
c
DropStmt: DROP drop_type_name name_list opt_drop_behavior
{
DropStmt *n = makeNode(DropStmt);
n->removeType = $2;
n->missing_ok = false;
n->objects = $3;
n->behavior = $4;
n->concurrent = false;
$$ = (Node *) n;
}
drop_type_name:
ACCESS METHOD { $$ = OBJECT_ACCESS_METHOD; }
| EVENT TRIGGER { $$ = OBJECT_EVENT_TRIGGER; }
| EXTENSION { $$ = OBJECT_EXTENSION; }
| FOREIGN DATA_P WRAPPER { $$ = OBJECT_FDW; }
| opt_procedural LANGUAGE { $$ = OBJECT_LANGUAGE; }
| PUBLICATION { $$ = OBJECT_PUBLICATION; }
| SCHEMA { $$ = OBJECT_SCHEMA; }
| SERVER { $$ = OBJECT_FOREIGN_SERVER; }
;
opt_drop_behavior:
CASCADE { $$ = DROP_CASCADE; }
| RESTRICT { $$ = DROP_RESTRICT; }
| /* EMPTY */ { $$ = DROP_RESTRICT; /* default */ }
;执行删除对象：
c
/*
* Drop one or more objects.
*
* We don't currently handle all object types here. Relations, for example,
* require special handling, because (for example) indexes have additional
* locking requirements.
*
* We look up all the objects first, and then delete them in a single
* performMultipleDeletions() call. This avoids unnecessary DROP RESTRICT
* errors if there are dependencies between them.
*/
void RemoveObjects(DropStmt *stmt)
{
ObjectAddresses *objects;
ListCell *cell1;
objects = new_object_addresses();
foreach(cell1, stmt->objects)
{
ObjectAddress address;
Node *object = lfirst(cell1);
Relation relation = NULL;
Oid namespaceId;
/* Get an ObjectAddress for the object. */
address = get_object_address(stmt->removeType,
object,
&relation,
AccessExclusiveLock,
stmt->missing_ok);
/*
* Issue NOTICE if supplied object was not found. Note this is only
* relevant in the missing_ok case, because otherwise
* get_object_address would have thrown an error.
*/
if (!OidIsValid(address.objectId))
{
Assert(stmt->missing_ok);
does_not_exist_skipping(stmt->removeType, object);
continue;
}
/*
* Although COMMENT ON FUNCTION, SECURITY LABEL ON FUNCTION, etc. are
* happy to operate on an aggregate as on any other function, we have
* historically not allowed this for DROP FUNCTION.
*/
if (stmt->removeType == OBJECT_FUNCTION)
{
if (get_func_prokind(address.objectId) == PROKIND_AGGREGATE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("\"%s\" is an aggregate function",
NameListToString(castNode(ObjectWithArgs, object)->objname)),
errhint("Use DROP AGGREGATE to drop aggregate functions.")));
}
/* Check permissions. */
namespaceId = get_object_namespace(&address);
if (!OidIsValid(namespaceId) ||
!pg_namespace_ownercheck(namespaceId, GetUserId()))
check_object_ownership(GetUserId(), stmt->removeType, address,
object, relation);
/*
* Make note if a temporary namespace has been accessed in this
* transaction.
*/
if (OidIsValid(namespaceId) && isTempNamespace(namespaceId))
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
/* Release any relcache reference count, but keep lock until commit. */
if (relation)
table_close(relation, NoLock);
add_exact_object_address(&address, objects);
}
/* Here we really delete them. */
performMultipleDeletions(objects, stmt->behavior, 0);
free_object_addresses(objects);
}