PostgreSQL源码学习调度器#14

• Z时代
• 2024-01-10
• 分类：综合

本节介绍PortalRun函数。

PortalRun函数

//src/include/tcop/pquery.h
extern bool PortalRun(Portal portal, long count, bool isTopLevel,
				  bool run_once, DestReceiver *dest, DestReceiver *altdest,
				  char *completionTag);

//src/backend/tcop/pquery.c
AssertArg(PortalIsValid(portal));
/* 动态追踪的探针 */
TRACE_POSTGRESQL_QUERY_EXECUTE_START();
/* 初始化completionTag */
if (completionTag)
	completionTag[0] = "";
/* 需要记录且portal策略不是multi_query时，在这里重置portal计时。
 * PORTAL_MULTI_QUERY 会为每个query分别计时（上节有讲） */
if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
{
	elog(DEBUG3, "PortalRun");
	ResetUsage();
}
/* 检查portal是否被错误使用，并标记portal为active状态 */
MarkPortalActive(portal);
/* 设置run_once标志 */
Assert(!portal->run_once || run_once);
portal->run_once = run_once;
/* 设置全局portal上下文指针 */
saveTopTransactionResourceOwner = TopTransactionResourceOwner;
saveTopTransactionContext = TopTransactionContext;
saveActivePortal = ActivePortal;
saveResourceOwner = CurrentResourceOwner;
savePortalContext = PortalContext;
saveMemoryContext = CurrentMemoryContext;
PG_TRY();
{
	ActivePortal = portal;
	if (portal->resowner)
		CurrentResourceOwner = portal->resowner;
	PortalContext = portal->portalContext;
	/* 切换到portal的内存上下文 */
	MemoryContextSwitchTo(PortalContext);
	switch (portal->strategy)
	{
		case PORTAL_ONE_SELECT:
		case PORTAL_ONE_RETURNING:
		case PORTAL_ONE_MOD_WITH:
		case PORTAL_UTIL_SELECT:
			/* 将结果存储在portal的tuplestore中 */
			if (portal->strategy != PORTAL_ONE_SELECT && !portal->holdStore)
				FillPortalStore(portal, isTopLevel);
			/* 获取所需的结果 */
			nprocessed = PortalRunSelect(portal, true, count, dest);
			/* 处理completionTag */
			if (completionTag && portal->commandTag)
			{
				if (strcmp(portal->commandTag, "SELECT") == 0)
					snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
							 "SELECT " UINT64_FORMAT, nprocessed);
				else
					strcpy(completionTag, portal->commandTag);
			}
			/* 标记portal为no active状态 */
			portal->status = PORTAL_READY;
			/* 当且仅当atEnd为true时表示处理完成了 */
			result = portal->atEnd;
			break;
		/* 需要有多个query分开处理 */
		case PORTAL_MULTI_QUERY:
			PortalRunMulti(portal, isTopLevel, false,
						   dest, altdest, completionTag);
			/* 防止portal的命令被重新执行 */
			MarkPortalDone(portal);
			/* 这里总是true  */
			result = true;
			break;
		default:
			elog(ERROR, "unrecognized portal strategy: %d",
				 (int) portal->strategy);
			result = false; /* keep compiler quiet */
			break;
	}
}
PG_CATCH();
{
	/* 出现未捕获的异常，标记portal为failed */
	MarkPortalFailed(portal);
	/* 恢复全局变量并传递错误 */
	if (saveMemoryContext == saveTopTransactionContext)
		MemoryContextSwitchTo(TopTransactionContext);
	else
		MemoryContextSwitchTo(saveMemoryContext);
	ActivePortal = saveActivePortal;
	if (saveResourceOwner == saveTopTransactionResourceOwner)
		CurrentResourceOwner = TopTransactionResourceOwner;
	else
		CurrentResourceOwner = saveResourceOwner;
	PortalContext = savePortalContext;
	PG_RE_THROW();
}
PG_END_TRY();
/*  恢复全局变量 */
if (saveMemoryContext == saveTopTransactionContext)
	MemoryContextSwitchTo(TopTransactionContext);
else
	MemoryContextSwitchTo(saveMemoryContext);
ActivePortal = saveActivePortal;
if (saveResourceOwner == saveTopTransactionResourceOwner)
	CurrentResourceOwner = TopTransactionResourceOwner;
else
	CurrentResourceOwner = saveResourceOwner;
PortalContext = savePortalContext;
/* 需要记录且portal策略不是multi_query时，在这里输出portal计时 */
if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
	ShowUsage("EXECUTOR STATISTICS");
/* 动态追踪的探针 */
TRACE_POSTGRESQL_QUERY_EXECUTE_DONE();
return result;

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