PostgreSQL中PortalRun->PortalRunSelect函数的实现逻辑是什么

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一、数据结构

Portal
对于Portals(客户端请求)，有几种执行策略，具体取决于要执行什么查询。
(注意:无论什么情况下，一个Portal只执行一个source-SQL查询，因此从用户的角度来看只产生一个结果。

/* * We have several execution strategies for Portals, depending on what * query or queries are to be executed.  (Note: in all cases, a Portal * executes just a single source-SQL query, and thus produces just a * single result from the user's viewpoint.  However, the rule rewriter * may expand the single source query to zero or many actual queries.) * 对于Portals(客户端请求)，有几种执行策略，具体取决于要执行什么查询。 * (注意:无论什么情况下，一个Portal只执行一个source-SQL查询，因此从用户的角度来看只产生一个结果。 * 但是，规则重写器可以将单个源查询扩展为零或多个实际查询。 *  * PORTAL_ONE_SELECT: the portal contains one single SELECT query.  We run * the Executor incrementally as results are demanded.  This strategy also * supports holdable cursors (the Executor results can be dumped into a * tuplestore for access after transaction completion). * PORTAL_ONE_SELECT: 包含一个SELECT查询。 *                    按需要的结果重复(递增)地运行执行器。 *                    该策略还支持可持有游标(执行器结果可以在事务完成后转储到tuplestore中进行访问)。 *  * PORTAL_ONE_RETURNING: the portal contains a single INSERT/UPDATE/DELETE * query with a RETURNING clause (plus possibly auxiliary queries added by * rule rewriting).  On first execution, we run the portal to completion * and dump the primary query's results into the portal tuplestore; the * results are then returned to the client as demanded.  (We can't support * suspension of the query partway through, because the AFTER TRIGGER code * can't cope, and also because we don't want to risk failing to execute * all the auxiliary queries.) * PORTAL_ONE_RETURNING: 包含一个带有RETURNING子句的INSERT/UPDATE/DELETE查询                         (可能还包括由规则重写添加的辅助查询)。 *                       在第一次执行时，运行Portal来完成并将主查询的结果转储到Portal的tuplestore中; *                       然后根据需要将结果返回给客户端。 *                       (我们不能支持半途中断的查询，因为AFTER触发器代码无法处理， *                       也因为不想冒执行所有辅助查询失败的风险)。 *  * PORTAL_ONE_MOD_WITH: the portal contains one single SELECT query, but * it has data-modifying CTEs.  This is currently treated the same as the * PORTAL_ONE_RETURNING case because of the possibility of needing to fire * triggers.  It may act more like PORTAL_ONE_SELECT in future. * PORTAL_ONE_MOD_WITH: 只包含一个SELECT查询，但它具有数据修改的CTEs。 *                      这与PORTAL_ONE_RETURNING的情况相同，因为可能需要触发触发器。将来它的行为可能更像PORTAL_ONE_SELECT。 *  * PORTAL_UTIL_SELECT: the portal contains a utility statement that returns * a SELECT-like result (for example, EXPLAIN or SHOW).  On first execution, * we run the statement and dump its results into the portal tuplestore; * the results are then returned to the client as demanded. * PORTAL_UTIL_SELECT: 包含一个实用程序语句，该语句返回一个类似SELECT的结果(例如，EXPLAIN或SHOW)。 *                     在第一次执行时，运行语句并将其结果转储到portal tuplestore;然后根据需要将结果返回给客户端。 *  * PORTAL_MULTI_QUERY: all other cases.  Here, we do not support partial * execution: the portal's queries will be run to completion on first call. * PORTAL_MULTI_QUERY: 除上述情况外的其他情况。 *                     在这里，不支持部分执行:Portal的查询语句将在第一次调用时运行到完成。 */typedef enum PortalStrategy{    PORTAL_ONE_SELECT,    PORTAL_ONE_RETURNING,    PORTAL_ONE_MOD_WITH,    PORTAL_UTIL_SELECT,    PORTAL_MULTI_QUERY} PortalStrategy;/* * A portal is always in one of these states.  It is possible to transit * from ACTIVE back to READY if the query is not run to completion; * otherwise we never back up in status. * Portal总是处于这些状态中的之一。 * 如果查询没有运行到完成，则可以从活动状态转回准备状态;否则永远不会后退。 */typedef enum PortalStatus{    PORTAL_NEW,                 /* 刚创建;freshly created */    PORTAL_DEFINED,             /* PortalDefineQuery完成;PortalDefineQuery done */    PORTAL_READY,               /* PortalStart完成;PortalStart complete, can run it */    PORTAL_ACTIVE,              /* Portal正在运行;portal is running (can't delete it) */    PORTAL_DONE,                /* Portal已经完成;portal is finished (don't re-run it) */    PORTAL_FAILED               /* Portal出现错误;portal got error (can't re-run it) */} PortalStatus;typedef struct PortalData *Portal;//结构体指针typedef struct PortalData{    /* Bookkeeping data */    const char *name;           /* portal的名称;portal's name */    const char *prepStmtName;   /* 已完成准备的源语句;source prepared statement (NULL if none) */    MemoryContext portalContext;    /* 内存上下文;subsidiary memory for portal */    ResourceOwner resowner;     /* 资源的owner;resources owned by portal */    void        (*cleanup) (Portal portal); /* cleanup钩子函数;cleanup hook */    /*     * State data for remembering which subtransaction(s) the portal was     * created or used in.  If the portal is held over from a previous     * transaction, both subxids are InvalidSubTransactionId.  Otherwise,     * createSubid is the creating subxact and activeSubid is the last subxact     * in which we ran the portal.     * 状态数据，用于记住在哪个子事务中创建或使用Portal。     * 如果Portal是从以前的事务中持有的，那么两个subxids都应该是InvalidSubTransactionId。     * 否则，createSubid是正在创建的subxact，而activeSubid是运行Portal的最后一个subxact。     */    SubTransactionId createSubid;   /* 正在创建的subxact;the creating subxact */    SubTransactionId activeSubid;   /* 活动的最后一个subxact;the last subxact with activity */    /* The query or queries the portal will execute */    //portal将会执行的查询    const char *sourceText;     /* 查询的源文本;text of query (as of 8.4, never NULL) */    const char *commandTag;     /* 源查询的命令tag;command tag for original query */    List       *stmts;          /* PlannedStmt链表;list of PlannedStmts */    CachedPlan *cplan;          /* 缓存的PlannedStmts;CachedPlan, if stmts are from one */    ParamListInfo portalParams; /* 传递给查询的参数;params to pass to query */    QueryEnvironment *queryEnv; /* 查询的执行环境;environment for query */    /* Features/options */    PortalStrategy strategy;    /* 场景;see above */    int         cursorOptions;  /* DECLARE CURSOR选项位;DECLARE CURSOR option bits */    bool        run_once;       /* 是否只执行一次;portal will only be run once */    /* Status data */    PortalStatus status;        /* Portal的状态;see above */    bool        portalPinned;   /* 是否不能被清除;a pinned portal can't be dropped */    bool        autoHeld;       /* 是否自动从pinned到held;was automatically converted from pinned to                                 * held (see HoldPinnedPortals()) */    /* If not NULL, Executor is active; call ExecutorEnd eventually: */    //如不为NULL,执行器处于活动状态    QueryDesc  *queryDesc;      /* 执行器需要使用的信息;info needed for executor invocation */    /* If portal returns tuples, this is their tupdesc: */    //如Portal需要返回元组,这是元组的描述    TupleDesc   tupDesc;        /* 结果元组的描述;descriptor for result tuples */    /* and these are the format codes to use for the columns: */    //列信息的格式码    int16      *formats;        /* 每一列的格式码;a format code for each column */    /*     * Where we store tuples for a held cursor or a PORTAL_ONE_RETURNING or     * PORTAL_UTIL_SELECT query.  (A cursor held past the end of its     * transaction no longer has any active executor state.)     * 在这里，为持有的游标或PORTAL_ONE_RETURNING或PORTAL_UTIL_SELECT存储元组。     * (在事务结束后持有的游标不再具有任何活动执行器状态。)     */    Tuplestorestate *holdStore; /* 存储持有的游标信息;store for holdable cursors */    MemoryContext holdContext;  /* 持有holdStore的内存上下文;memory containing holdStore */    /*     * Snapshot under which tuples in the holdStore were read.  We must keep a     * reference to this snapshot if there is any possibility that the tuples     * contain TOAST references, because releasing the snapshot could allow     * recently-dead rows to be vacuumed away, along with any toast data     * belonging to them.  In the case of a held cursor, we avoid needing to     * keep such a snapshot by forcibly detoasting the data.     * 读取holdStore中元组的Snapshot。     * 如果元组包含TOAST引用的可能性存在，那么必须保持对该快照的引用，     * 因为释放快照可能会使最近废弃的行与属于它们的TOAST数据一起被清除。     * 对于持有的游标，通过强制解压数据来避免需要保留这样的快照。     */    Snapshot    holdSnapshot;   /* 已注册的快照信息,如无则为NULL;registered snapshot, or NULL if none */    /*     * atStart, atEnd and portalPos indicate the current cursor position.     * portalPos is zero before the first row, N after fetching N'th row of     * query.  After we run off the end, portalPos = # of rows in query, and     * atEnd is true.  Note that atStart implies portalPos == 0, but not the     * reverse: we might have backed up only as far as the first row, not to     * the start.  Also note that various code inspects atStart and atEnd, but     * only the portal movement routines should touch portalPos.     * atStart、atEnd和portalPos表示当前光标的位置。     * portalPos在第一行之前为0，在获取第N行查询后为N。     * 在运行结束后，portalPos = #查询中的行号，atEnd为T。     * 注意，atStart表示portalPos == 0，但不是相反:我们可能只回到到第一行，而不是开始。     * 还要注意，各种代码在开始和结束时都要检查，但是只有Portal移动例程应该访问portalPos。     */    bool        atStart;//处于开始位置?    bool        atEnd;//处于结束位置?    uint64      portalPos;//实际行号    /* Presentation data, primarily used by the pg_cursors system view */    //用于表示的数据，主要由pg_cursors系统视图使用    TimestampTz creation_time;  /* portal定义的时间;time at which this portal was defined */    bool        visible;        /* 是否在pg_cursors中可见? include this portal in pg_cursors? */}           PortalData;/* * PortalIsValid *      True iff portal is valid. *      判断Portal是否有效 */#define PortalIsValid(p) PointerIsValid(p)

QueryDesc
QueryDesc封装了执行器执行查询所需的所有内容。

/* ---------------- *      query descriptor: * *  a QueryDesc encapsulates everything that the executor *  needs to execute the query. *  QueryDesc封装了执行器执行查询所需的所有内容。 * *  For the convenience of SQL-language functions, we also support QueryDescs *  containing utility statements; these must not be passed to the executor *  however. *  为了使用SQL函数，还需要支持包含实用语句的QueryDescs; *  但是，这些内容不能传递给执行程序。 * --------------------- */typedef struct QueryDesc{    /* These fields are provided by CreateQueryDesc */    //以下变量由CreateQueryDesc函数设置    CmdType     operation;      /* 操作类型,如CMD_SELECT等;CMD_SELECT, CMD_UPDATE, etc. */    PlannedStmt *plannedstmt;   /* 已规划的语句,规划器的输出;planner's output (could be utility, too) */    const char *sourceText;     /* 源SQL文本;source text of the query */    Snapshot    snapshot;       /* 查询使用的快照;snapshot to use for query */    Snapshot    crosscheck_snapshot;    /* RI 更新/删除交叉检查快照;crosscheck for RI update/delete */    DestReceiver *dest;         /* 元组输出的接收器;the destination for tuple output */    ParamListInfo params;       /* 需传入的参数值;param values being passed in */    QueryEnvironment *queryEnv; /* 查询环境变量;query environment passed in */    int         instrument_options; /* InstrumentOption选项;OR of InstrumentOption flags */    /* These fields are set by ExecutorStart */    //以下变量由ExecutorStart函数设置    TupleDesc   tupDesc;        /* 结果元组tuples描述;descriptor for result tuples */    EState     *estate;         /* 执行器状态;executor's query-wide state */    PlanState  *planstate;      /* per-plan-node状态树;tree of per-plan-node state */    /* This field is set by ExecutorRun */    //以下变量由ExecutorRun设置    bool        already_executed;   /* 先前已执行,则为T;true if previously executed */    /* This is always set NULL by the core system, but plugins can change it */    //内核设置为NULL,可由插件修改    struct Instrumentation *totaltime;  /* ExecutorRun函数所花费的时间;total time spent in ExecutorRun */} QueryDesc;

二、源码解读

PortalRun->PortalRunSelect函数执行以PORTAL_ONE_SELECT模式运行的SQL.

/* * PortalRunSelect *      Execute a portal's query in PORTAL_ONE_SELECT mode, and also *      when fetching from a completed holdStore in PORTAL_ONE_RETURNING, *      PORTAL_ONE_MOD_WITH, and PORTAL_UTIL_SELECT cases. *       执行以PORTAL_ONE_SELECT模式运行的SQL,同时处理PORTAL_ONE_RETURNING/ *      PORTAL_ONE_MOD_WITH/PORTAL_UTIL_SELECT这几种模式下完成holdStore后的数据提取 * * This handles simple N-rows-forward-or-backward cases.  For more complex * nonsequential access to a portal, see PortalRunFetch. * 这将处理简单的n行前向或后向情况。 * 有关对门户的更复杂的非顺序访问，请参阅PortalRunFetch。 *  * count <= 0 is interpreted as a no-op: the destination gets started up * and shut down, but nothing else happens.  Also, count == FETCH_ALL is * interpreted as "all rows".  (cf FetchStmt.howMany) * count <= 0被解释为一个no-op:目标启动并关闭，但是没有发生其他事情。 * 另外，count == FETCH_ALL被解释为"所有行"。(cf FetchStmt.howMany) *  * Caller must already have validated the Portal and done appropriate * setup (cf. PortalRun). * 调用者必须完成Portal的校验以及相关的配置. * * Returns number of rows processed (suitable for use in result tag) * 返回已处理的行数. */static uint64PortalRunSelect(Portal portal,                bool forward,                long count,                DestReceiver *dest){    QueryDesc  *queryDesc;    ScanDirection direction;    uint64      nprocessed;    /*     * NB: queryDesc will be NULL if we are fetching from a held cursor or a     * completed utility query; can't use it in that path.     * 注意:从已持有的游标或者已完成的工具类查询中返回时,queryDesc有可能是NULL.     */    queryDesc = portal->queryDesc;    /* Caller messed up if we have neither a ready query nor held data. */    //确保queryDescbuweiNULL或者持有提取的数据    Assert(queryDesc || portal->holdStore);    /*     * Force the queryDesc destination to the right thing.  This supports     * MOVE, for example, which will pass in dest = DestNone.  This is okay to     * change as long as we do it on every fetch.  (The  must not     * assume that dest never changes.)     * 确保queryDesc目的地是正确的地方。     * 例如，它支持MOVE，它将传入dest = DestNone。     * 只要在每次取回时都这样做，这是可以改变的。(Executor不能假定dest永不改变。)     */    if (queryDesc)        queryDesc->dest = dest;//设置dest    /*     * Determine which direction to go in, and check to see if we're already     * at the end of the available tuples in that direction.  If so, set the     * direction to NoMovement to avoid trying to fetch any tuples.  (This     * check exists because not all plan node types are robust about being     * called again if they've already returned NULL once.)  Then call the     * executor (we must not skip this, because the destination needs to see a     * setup and shutdown even if no tuples are available).  Finally, update     * the portal position state depending on the number of tuples that were     * retrieved.     * 确定要进入的方向，并检查是否已经在该方向的可用元组的末尾。     * 如果是这样，则将方向设置为NoMovement，以避免试图再次获取任何元组。     * (之所以存在这种检查，是因为不是所有的计划节点类型都能够在已经返回NULL时再次调用。)     * 然后调用executor(我们不能跳过这一步，因为目标需要看到设置和关闭，即使没有元组可用)。     * 最后，根据检索到的元组数量更新Portal的数据位置状态。     */    if (forward)//前向    {        if (portal->atEnd || count <= 0)        {            //已到末尾或者行计数小于等于0            direction = NoMovementScanDirection;            count = 0;          /* don't pass negative count to executor */        }        else            direction = ForwardScanDirection;//前向扫描        /* In the executor, zero count processes all rows */        //在executor中,count=0意味着提取所有行        if (count == FETCH_ALL)            count = 0;        if (portal->holdStore)            //持有提取后的数据游标            nprocessed = RunFromStore(portal, direction, (uint64) count, dest);        else        {            //没有持有游标(数据)            PushActiveSnapshot(queryDesc->snapshot);//快照入栈            ExecutorRun(queryDesc, direction, (uint64) count,                        portal->run_once);//开始执行            nprocessed = queryDesc->estate->es_processed;//结果行数            PopActiveSnapshot();//快照出栈        }        if (!ScanDirectionIsNoMovement(direction))//扫描方向可移动        {            if (nprocessed > 0)//扫描行数>0                portal->atStart = false;    /* 可以向前移动了;OK to go backward now */            if (count == 0 || nprocessed < (uint64) count)                //count为0或者行数小于传入的计数器                portal->atEnd = true;   /* 已完成扫描;we retrieved 'em all */            portal->portalPos += nprocessed;//位置移动(+处理行数)        }    }    else//非前向(后向)    {        if (portal->cursorOptions & CURSOR_OPT_NO_SCROLL)//如游标不可移动,报错            ereport(ERROR,                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),                     errmsg("cursor can only scan forward"),                     errhint("Declare it with SCROLL option to enable backward scan.")));        if (portal->atStart || count <= 0)        {            //处于开始或者count小于等于0            direction = NoMovementScanDirection;            count = 0;          /* don't pass negative count to executor */        }        else            //往后扫描            direction = BackwardScanDirection;        /* In the executor, zero count processes all rows */        //参见forward=T的注释        if (count == FETCH_ALL)            count = 0;        if (portal->holdStore)            nprocessed = RunFromStore(portal, direction, (uint64) count, dest);        else        {            PushActiveSnapshot(queryDesc->snapshot);            ExecutorRun(queryDesc, direction, (uint64) count,                        portal->run_once);            nprocessed = queryDesc->estate->es_processed;            PopActiveSnapshot();        }        if (!ScanDirectionIsNoMovement(direction))        {            if (nprocessed > 0 && portal->atEnd)            {                portal->atEnd = false;  /* OK to go forward now */                portal->portalPos++;    /* adjust for endpoint case */            }            if (count == 0 || nprocessed < (uint64) count)            {                portal->atStart = true; /* we retrieved 'em all */                portal->portalPos = 0;            }            else            {                portal->portalPos -= nprocessed;            }        }    }    return nprocessed;}/* * RunFromStore *      Fetch tuples from the portal's tuple store. *      从Portal的tuple store中提取元组. * * Calling conventions are similar to ExecutorRun, except that we * do not depend on having a queryDesc or estate.  Therefore we return the * number of tuples processed as the result, not in estate->es_processed. * 该函数的调用约定类似于ExecutorRun，只是不依赖于是否拥有queryDesc或estate。 * 因此，返回处理的元组的数量作为结果，而不是在estate->es_processed中返回。 *  * One difference from ExecutorRun is that the destination receiver functions * are run in the caller's memory context (since we have no estate).  Watch * out for memory leaks. * 与ExecutorRun不同的是，目标接收器函数在调用者的内存上下文中运行(因为没有estate)。 * 需注意内存泄漏!!! */static uint64RunFromStore(Portal portal, ScanDirection direction, uint64 count,             DestReceiver *dest){    uint64      current_tuple_count = 0;    TupleTableSlot *slot;//元组表slot    slot = MakeSingleTupleTableSlot(portal->tupDesc);    dest->rStartup(dest, CMD_SELECT, portal->tupDesc);//目标启动    if (ScanDirectionIsNoMovement(direction))//无法移动    {        /* do nothing except start/stop the destination */        //不需要做任何事情    }    else    {        bool        forward = ScanDirectionIsForward(direction);//是否前向扫描        for (;;)//循环        {            MemoryContext oldcontext;//内存上下文            bool        ok;            oldcontext = MemoryContextSwitchTo(portal->holdContext);//切换至相应的内存上下文            ok = tuplestore_gettupleslot(portal->holdStore, forward, false,                                         slot);//获取元组            MemoryContextSwitchTo(oldcontext);//切换回原上下文            if (!ok)                break;//如出错,则跳出循环            /*             * If we are not able to send the tuple, we assume the destination             * has closed and no more tuples can be sent. If that's the case,             * end the loop.             * 如果不能发送元组到目标端，那么我们假设目标端已经关闭，不能发送更多元组。             * 如果是这样，结束循环。             */            if (!dest->receiveSlot(slot, dest))                break;            ExecClearTuple(slot);//执行清理            /*             * check our tuple count.. if we've processed the proper number             * then quit, else loop again and process more tuples. Zero count             * means no limit.             * 检查元组计数…如果处理了正确的计数，那么退出，             * 否则再次循环并处理更多元组。零计数意味着没有限制。             */            current_tuple_count++;            if (count && count == current_tuple_count)                break;        }    }    dest->rShutdown(dest);//关闭目标端    ExecDropSingleTupleTableSlot(slot);//清除slot    return current_tuple_count;//返回行数} /* ---------------------------------------------------------------- *      ExecutorRun *      ExecutorRun函数 * *      This is the main routine of the executor module. It accepts *      the query descriptor from the traffic cop and executes the *      query plan. *      这是executor模块的主要实现例程。它接受traffic cop的查询描述符并执行查询计划。 * *      ExecutorStart must have been called already. *      在此之前,已调用ExecutorStart函数. *   *      If direction is NoMovementScanDirection then nothing is done *      except to start up/shut down the destination.  Otherwise, *      we retrieve up to 'count' tuples in the specified direction. *      如果方向是NoMovementScanDirection，那么除了启动/关闭目标之外什么也不做。 *      否则，在指定的方向上检索指定数量"count"的元组。 * *      Note: count = 0 is interpreted as no portal limit, i.e., run to *      completion.  Also note that the count limit is only applied to *      retrieved tuples, not for instance to those inserted/updated/deleted *      by a ModifyTable plan node. *      注意:count = 0被解释为没有限制，即，运行到完成。 *      还要注意，计数限制只适用于检索到的元组，而不适用于由ModifyTable计划节点插入/更新/删除的元组。 * *      There is no return value, but output tuples (if any) are sent to *      the destination receiver specified in the QueryDesc; and the number *      of tuples processed at the top level can be found in *      estate->es_processed. *      没有返回值，但是输出元组(如果有的话)被发送到QueryDesc中指定的目标接收器; *      在顶层处理的元组数量可以在estate-> es_processing中找到。 * *      We provide a function hook variable that lets loadable plugins *      get control when ExecutorRun is called.  Such a plugin would *      normally call standard_ExecutorRun(). *      我们提供了一个钩子函数变量，可以让插件在调用ExecutorRun时获得控制权。 *      这样的插件通常会调用standard_ExecutorRun()函数。 * * ---------------------------------------------------------------- */voidExecutorRun(QueryDesc *queryDesc,            ScanDirection direction, uint64 count,            bool execute_once){    if (ExecutorRun_hook)        (*ExecutorRun_hook) (queryDesc, direction, count, execute_once);//钩子函数    else        standard_ExecutorRun(queryDesc, direction, count, execute_once);//标准函数}voidstandard_ExecutorRun(QueryDesc *queryDesc,                     ScanDirection direction, uint64 count, bool execute_once){    EState     *estate;//全局执行状态    CmdType     operation;//命令类型    DestReceiver *dest;//接收器    bool        sendTuples;//是否需要传输元组    MemoryContext oldcontext;//内存上下文    /* sanity checks */    Assert(queryDesc != NULL);//校验queryDesc不能为NULL    estate = queryDesc->estate;//获取执行状态    Assert(estate != NULL);//执行状态不能为NULL    Assert(!(estate->es_top_eflags & EXEC_FLAG_EXPLAIN_ONLY));//eflags标记不能为EXEC_FLAG_EXPLAIN_ONLY    /*     * Switch into per-query memory context     * 切换内存上下文     */    oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);    /* Allow instrumentation of Executor overall runtime */    //允许全程instrumentation    if (queryDesc->totaltime)        InstrStartNode(queryDesc->totaltime);    /*     * extract information from the query descriptor and the query feature.     * 从查询描述符和查询特性中提取信息。     */    operation = queryDesc->operation;    dest = queryDesc->dest;    /*     * startup tuple receiver, if we will be emitting tuples     * 如需发送元组,则启动元组接收器     */    estate->es_processed = 0;    estate->es_lastoid = InvalidOid;    sendTuples = (operation == CMD_SELECT ||                  queryDesc->plannedstmt->hasReturning);    if (sendTuples)//如需发送元组        dest->rStartup(dest, operation, queryDesc->tupDesc);    /*     * run plan     * 执行Plan     */    if (!ScanDirectionIsNoMovement(direction))//如非ScanDirectionIsNoMovement    {        if (execute_once && queryDesc->already_executed)//校验            elog(ERROR, "can't re-execute query flagged for single execution");        queryDesc->already_executed = true;//修改标记        ExecutePlan(estate,                    queryDesc->planstate,                    queryDesc->plannedstmt->parallelModeNeeded,                    operation,                    sendTuples,                    count,                    direction,                    dest,                    execute_once);//执行Plan    }    /*     * shutdown tuple receiver, if we started it     * 如启动了元组接收器,则关闭它     */    if (sendTuples)        dest->rShutdown(dest);    if (queryDesc->totaltime)//收集时间        InstrStopNode(queryDesc->totaltime, estate->es_processed);    MemoryContextSwitchTo(oldcontext);//切换内存上下文}

三、跟踪分析

测试脚本如下

testdb=# explain select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je testdb-# from t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je testdb(#                         from t_grxx gr inner join t_jfxx jf testdb(#                                        on gr.dwbh = dw.dwbh testdb(#                                           and gr.grbh = jf.grbh) grjftestdb-# order by dw.dwbh;                                        QUERY PLAN                                        ------------------------------------------------------------------------------------------ Sort  (cost=20070.93..20320.93 rows=100000 width=47)   Sort Key: dw.dwbh   ->  Hash Join  (cost=3754.00..8689.61 rows=100000 width=47)         Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)         ->  Hash Join  (cost=3465.00..8138.00 rows=100000 width=31)               Hash Cond: ((jf.grbh)::text = (gr.grbh)::text)               ->  Seq Scan on t_jfxx jf  (cost=0.00..1637.00 rows=100000 width=20)               ->  Hash  (cost=1726.00..1726.00 rows=100000 width=16)                     ->  Seq Scan on t_grxx gr  (cost=0.00..1726.00 rows=100000 width=16)         ->  Hash  (cost=164.00..164.00 rows=10000 width=20)               ->  Seq Scan on t_dwxx dw  (cost=0.00..164.00 rows=10000 width=20)(11 rows)

启动gdb,设置断点,进入PortalRunSelect

(gdb) b PortalRunSelectBreakpoint 1 at 0x8cc0e8: file pquery.c, line 888.(gdb) cContinuing.Breakpoint 1, PortalRunSelect (portal=0x1af2468, forward=true, count=9223372036854775807, dest=0x1b74668) at pquery.c:888warning: Source file is more recent than executable.888     queryDesc = portal->queryDesc;(gdb)

查看输入参数portal&dest,forward为T表示前向扫描
portal:未命名的Portal,holdStore为NULL,atStart = true, atEnd = false, portalPos = 0
dest:接收器slot为printtup

(gdb) p *portal$1 = {name = 0x1af5e90 "", prepStmtName = 0x0, portalContext = 0x1b795d0, resowner = 0x1abde80,   cleanup = 0x6711b6 , createSubid = 1, activeSubid = 1,   sourceText = 0x1a8ceb8 "select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je \nfrom t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je \n", ' ' , "from t_grxx gr inner join t_jfxx jf \n", ' ' ...,   commandTag = 0xc5eed5 "SELECT", stmts = 0x1b74630, cplan = 0x0, portalParams = 0x0, queryEnv = 0x0,   strategy = PORTAL_ONE_SELECT, cursorOptions = 4, run_once = true, status = PORTAL_ACTIVE, portalPinned = false,   autoHeld = false, queryDesc = 0x1b796e8, tupDesc = 0x1b867d8, formats = 0x1b79780, holdStore = 0x0, holdContext = 0x0,   holdSnapshot = 0x0, atStart = true, atEnd = false, portalPos = 0, creation_time = 595566906253867, visible = false}(gdb) p *dest$2 = {receiveSlot = 0x48cc00 , rStartup = 0x48c5c1 , rShutdown = 0x48d02e ,   rDestroy = 0x48d0a7 , mydest = DestRemote}

校验并设置dest

(gdb) n891     Assert(queryDesc || portal->holdStore);(gdb) 899     if (queryDesc)(gdb) 900         queryDesc->dest = dest;

前向扫描

(gdb) n913     if (forward)(gdb) 915         if (portal->atEnd || count <= 0)

进入ExecutorRun

...(gdb) 932             ExecutorRun(queryDesc, direction, (uint64) count,(gdb) stepExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:304warning: Source file is more recent than executable.304     if (ExecutorRun_hook)

进入standard_ExecutorRun

(gdb) n307         standard_ExecutorRun(queryDesc, direction, count, execute_once);(gdb) stepstandard_ExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:321321     Assert(queryDesc != NULL);

standard_ExecutorRun->校验并切换上下文

321     Assert(queryDesc != NULL);(gdb) n323     estate = queryDesc->estate;(gdb) 325     Assert(estate != NULL);(gdb) 326     Assert(!(estate->es_top_eflags & EXEC_FLAG_EXPLAIN_ONLY));(gdb) 331     oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);(gdb)

standard_ExecutorRun->变量赋值,判断是否需要传输元组

(gdb) 334     if (queryDesc->totaltime)(gdb) n340     operation = queryDesc->operation;(gdb) 341     dest = queryDesc->dest;(gdb) p operation$3 = CMD_SELECT(gdb) n346     estate->es_processed = 0;(gdb) 347     estate->es_lastoid = InvalidOid;(gdb) 349     sendTuples = (operation == CMD_SELECT ||(gdb) 352     if (sendTuples)(gdb) 353         dest->rStartup(dest, operation, queryDesc->tupDesc);(gdb) p sendTuples$4 = true(gdb)

standard_ExecutorRun->执行计划(ExecutePlan函数下节介绍)

(gdb) n358     if (!ScanDirectionIsNoMovement(direction))(gdb) 360         if (execute_once && queryDesc->already_executed)(gdb) 362         queryDesc->already_executed = true;(gdb) 364         ExecutePlan(estate,(gdb)

standard_ExecutorRun->关闭资源并切换上下文

(gdb) 378     if (sendTuples)(gdb) n379         dest->rShutdown(dest);(gdb) 381     if (queryDesc->totaltime)(gdb) 384     MemoryContextSwitchTo(oldcontext);(gdb) 385 }(gdb)

standard_ExecutorRun->回到PortalRunSelect

(gdb) nExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:308308 }(gdb) PortalRunSelect (portal=0x1af2468, forward=true, count=0, dest=0x1b74668) at pquery.c:934934             nprocessed = queryDesc->estate->es_processed;

快照出栈,修改状态atStart/atEnd等

(gdb) n935             PopActiveSnapshot();(gdb) 938         if (!ScanDirectionIsNoMovement(direction))(gdb) 940             if (nprocessed > 0)(gdb) p nprocessed$6 = 99991(gdb) n941                 portal->atStart = false;    /* OK to go backward now */(gdb) 942             if (count == 0 || nprocessed < (uint64) count)(gdb)

完成调用

(gdb) n943                 portal->atEnd = true;   /* we retrieved 'em all */(gdb) p count$7 = 0(gdb) n944             portal->portalPos += nprocessed;(gdb) 997     return nprocessed;(gdb) 998 }(gdb) nPortalRun (portal=0x1af2468, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x1b74668, altdest=0x1b74668,     completionTag=0x7ffc5ff58740 "") at pquery.c:780780                 if (completionTag && portal->commandTag)(gdb) p nprocessed$8 = 99991

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