prepare.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	oldcxt = MemoryContextSwitchTo(entrycxt);

	/*
	 * We need to copy the data so that it is stored in the correct memory
	 * context.  Do this before making hashtable entry, so that an
	 * out-of-memory failure only wastes memory and doesn't leave us with an
	 * incomplete (ie corrupt) hashtable entry.
	 */
	qstring = query_string ? pstrdup(query_string) : NULL;
	query_list = (List *) copyObject(query_list);
	plan_list = (List *) copyObject(plan_list);
	argtype_list = list_copy(argtype_list);

	/* Now we can add entry to hash table */
	entry = (PreparedStatement *) hash_search(prepared_queries,
											  key,
											  HASH_ENTER,
											  &found);

	/* Shouldn't get a duplicate entry */
	if (found)
		elog(ERROR, "duplicate prepared statement \"%s\"",
			 stmt_name);

	/* Fill in the hash table entry with copied data */
	entry->query_string = qstring;
	entry->commandTag = commandTag;
	entry->query_list = query_list;
	entry->plan_list = plan_list;
	entry->argtype_list = argtype_list;
	entry->context = entrycxt;

	MemoryContextSwitchTo(oldcxt);
}

/*
 * Lookup an existing query in the hash table. If the query does not
 * actually exist, throw ereport(ERROR) or return NULL per second parameter.
 */
PreparedStatement *
FetchPreparedStatement(const char *stmt_name, bool throwError)
{
	char		key[NAMEDATALEN];
	PreparedStatement *entry;

	/*
	 * If the hash table hasn't been initialized, it can't be storing
	 * anything, therefore it couldn't possibly store our plan.
	 */
	if (prepared_queries)
	{
		/*
		 * We can't just use the statement name as supplied by the user: the
		 * hash package is picky enough that it needs to be NULL-padded out to
		 * the appropriate length to work correctly.
		 */
		StrNCpy(key, stmt_name, sizeof(key));

		entry = (PreparedStatement *) hash_search(prepared_queries,
												  key,
												  HASH_FIND,
												  NULL);
	}
	else
		entry = NULL;

	if (!entry && throwError)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_PSTATEMENT),
				 errmsg("prepared statement \"%s\" does not exist",
						stmt_name)));

	return entry;
}

/*
 * Look up a prepared statement given the name (giving error if not found).
 * If found, return the list of argument type OIDs.
 */
List *
FetchPreparedStatementParams(const char *stmt_name)
{
	PreparedStatement *entry;

	entry = FetchPreparedStatement(stmt_name, true);

	return entry->argtype_list;
}

/*
 * Given a prepared statement, determine the result tupledesc it will
 * produce.  Returns NULL if the execution will not return tuples.
 *
 * Note: the result is created or copied into current memory context.
 */
TupleDesc
FetchPreparedStatementResultDesc(PreparedStatement *stmt)
{
	Query	   *query;

	switch (ChoosePortalStrategy(stmt->query_list))
	{
		case PORTAL_ONE_SELECT:
			query = (Query *) linitial(stmt->query_list);
			return ExecCleanTypeFromTL(query->targetList, false);

		case PORTAL_UTIL_SELECT:
			query = (Query *) linitial(stmt->query_list);
			return UtilityTupleDescriptor(query->utilityStmt);

		case PORTAL_MULTI_QUERY:
			/* will not return tuples */
			break;
	}
	return NULL;
}

/*
 * Given a prepared statement, determine whether it will return tuples.
 *
 * Note: this is used rather than just testing the result of
 * FetchPreparedStatementResultDesc() because that routine can fail if
 * invoked in an aborted transaction.  This one is safe to use in any
 * context.  Be sure to keep the two routines in sync!
 */
bool
PreparedStatementReturnsTuples(PreparedStatement *stmt)
{
	switch (ChoosePortalStrategy(stmt->query_list))
	{
		case PORTAL_ONE_SELECT:
		case PORTAL_UTIL_SELECT:
			return true;

		case PORTAL_MULTI_QUERY:
			/* will not return tuples */
			break;
	}
	return false;
}

/*
 * Given a prepared statement that returns tuples, extract the query
 * targetlist.	Returns NIL if the statement doesn't have a determinable
 * targetlist.
 *
 * Note: do not modify the result.
 *
 * XXX be careful to keep this in sync with FetchPortalTargetList,
 * and with UtilityReturnsTuples.
 */
List *
FetchPreparedStatementTargetList(PreparedStatement *stmt)
{
	PortalStrategy strategy = ChoosePortalStrategy(stmt->query_list);

	if (strategy == PORTAL_ONE_SELECT)
		return ((Query *) linitial(stmt->query_list))->targetList;
	if (strategy == PORTAL_UTIL_SELECT)
	{
		Node	   *utilityStmt;

		utilityStmt = ((Query *) linitial(stmt->query_list))->utilityStmt;
		switch (nodeTag(utilityStmt))
		{
			case T_FetchStmt:
				{
					FetchStmt  *substmt = (FetchStmt *) utilityStmt;
					Portal		subportal;

					Assert(!substmt->ismove);
					subportal = GetPortalByName(substmt->portalname);
					Assert(PortalIsValid(subportal));
					return FetchPortalTargetList(subportal);
				}

			case T_ExecuteStmt:
				{
					ExecuteStmt *substmt = (ExecuteStmt *) utilityStmt;
					PreparedStatement *entry;

					Assert(!substmt->into);
					entry = FetchPreparedStatement(substmt->name, true);
					return FetchPreparedStatementTargetList(entry);
				}

			default:
				break;
		}
	}
	return NIL;
}

/*
 * Implements the 'DEALLOCATE' utility statement: deletes the
 * specified plan from storage.
 */
void
DeallocateQuery(DeallocateStmt *stmt)
{
	DropPreparedStatement(stmt->name, true);
}

/*
 * Internal version of DEALLOCATE
 *
 * If showError is false, dropping a nonexistent statement is a no-op.
 */
void
DropPreparedStatement(const char *stmt_name, bool showError)
{
	PreparedStatement *entry;

	/* Find the query's hash table entry; raise error if wanted */
	entry = FetchPreparedStatement(stmt_name, showError);

	if (entry)
	{
		/* Drop any open portals that depend on this prepared statement */
		Assert(MemoryContextIsValid(entry->context));
		DropDependentPortals(entry->context);

		/* Flush the context holding the subsidiary data */
		MemoryContextDelete(entry->context);

		/* Now we can remove the hash table entry */
		hash_search(prepared_queries, entry->stmt_name, HASH_REMOVE, NULL);
	}
}

/*
 * Implements the 'EXPLAIN EXECUTE' utility statement.
 */
void
ExplainExecuteQuery(ExplainStmt *stmt, TupOutputState *tstate)
{
	ExecuteStmt *execstmt = (ExecuteStmt *) stmt->query->utilityStmt;
	PreparedStatement *entry;
	ListCell   *q,
			   *p;
	List	   *query_list,
			   *plan_list;
	ParamListInfo paramLI = NULL;
	EState	   *estate = NULL;

	/* explain.c should only call me for EXECUTE stmt */
	Assert(execstmt && IsA(execstmt, ExecuteStmt));

	/* Look it up in the hash table */
	entry = FetchPreparedStatement(execstmt->name, true);

	query_list = entry->query_list;
	plan_list = entry->plan_list;

	Assert(list_length(query_list) == list_length(plan_list));

	/* Evaluate parameters, if any */
	if (entry->argtype_list != NIL)
	{
		/*
		 * Need an EState to evaluate parameters; must not delete it till end
		 * of query, in case parameters are pass-by-reference.
		 */
		estate = CreateExecutorState();
		paramLI = EvaluateParams(estate, execstmt->params,
								 entry->argtype_list);
	}

	/* Explain each query */
	forboth(q, query_list, p, plan_list)
	{
		Query	   *query = (Query *) lfirst(q);
		Plan	   *plan = (Plan *) lfirst(p);
		bool		is_last_query;

		is_last_query = (lnext(p) == NULL);

		if (query->commandType == CMD_UTILITY)
		{
			if (query->utilityStmt && IsA(query->utilityStmt, NotifyStmt))
				do_text_output_oneline(tstate, "NOTIFY");
			else
				do_text_output_oneline(tstate, "UTILITY");
		}
		else
		{
			QueryDesc  *qdesc;

			if (execstmt->into)
			{
				if (query->commandType != CMD_SELECT)
					ereport(ERROR,
							(errcode(ERRCODE_WRONG_OBJECT_TYPE),
							 errmsg("prepared statement is not a SELECT")));

				/* Copy the query so we can modify it */
				query = copyObject(query);

				query->into = execstmt->into;
			}

			/*
			 * Update snapshot command ID to ensure this query sees results of
			 * any previously executed queries.  (It's a bit cheesy to modify
			 * ActiveSnapshot without making a copy, but for the limited ways
			 * in which EXPLAIN can be invoked, I think it's OK, because the
			 * active snapshot shouldn't be shared with anything else anyway.)
			 */
			ActiveSnapshot->curcid = GetCurrentCommandId();

			/* Create a QueryDesc requesting no output */
			qdesc = CreateQueryDesc(query, plan,
									ActiveSnapshot, InvalidSnapshot,
									None_Receiver,
									paramLI, stmt->analyze);

			ExplainOnePlan(qdesc, stmt, tstate);
		}

		/* No need for CommandCounterIncrement, as ExplainOnePlan did it */

		/* put a blank line between plans */
		if (!is_last_query)
			do_text_output_oneline(tstate, "");
	}

	if (estate)
		FreeExecutorState(estate);
}