本节介绍了PortalRun->PortalRunSelect函数的实现逻辑，该函数执行以PORTAL_ONE_SELECT模式运行的SQL。
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 uint64
PortalRunSelect(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 uint64
RunFromStore(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。
*
* ----------------------------------------------------------------
*/
void
ExecutorRun(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
}
void
standard_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) grjf
testdb-# 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 PortalRunSelect
Breakpoint 1 at 0x8cc0e8: file pquery.c, line 888.
(gdb) c
Continuing.
Breakpoint 1, PortalRunSelect (portal=0x1af2468, forward=true, count=9223372036854775807, dest=0x1b74668) at pquery.c:888
warning: 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 <PortalCleanup>, 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", ' ' <repeats 24 times>, "from t_grxx gr inner join t_jfxx jf \n", ' ' <repeats 34 times>...,
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 <printtup>, rStartup = 0x48c5c1 <printtup_startup>, rShutdown = 0x48d02e <printtup_shutdown>,
rDestroy = 0x48d0a7 <printtup_destroy>, mydest = DestRemote}
校验并设置dest
(gdb) n
891 Assert(queryDesc || portal->holdStore);
(gdb)
899 if (queryDesc)
(gdb)
900 queryDesc->dest = dest;
前向扫描
(gdb) n
913 if (forward)
(gdb)
915 if (portal->atEnd || count <= 0)
进入ExecutorRun
...
(gdb)
932 ExecutorRun(queryDesc, direction, (uint64) count,
(gdb) step
ExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:304
warning: Source file is more recent than executable.
304 if (ExecutorRun_hook)
进入standard_ExecutorRun
(gdb) n
307 standard_ExecutorRun(queryDesc, direction, count, execute_once);
(gdb) step
standard_ExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:321
321 Assert(queryDesc != NULL);
standard_ExecutorRun->校验并切换上下文
321 Assert(queryDesc != NULL);
(gdb) n
323 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) n
340 operation = queryDesc->operation;
(gdb)
341 dest = queryDesc->dest;
(gdb) p operation
$3 = CMD_SELECT
(gdb) n
346 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) n
358 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) n
379 dest->rShutdown(dest);
(gdb)
381 if (queryDesc->totaltime)
(gdb)
384 MemoryContextSwitchTo(oldcontext);
(gdb)
385 }
(gdb)
standard_ExecutorRun->回到PortalRunSelect
(gdb) n
ExecutorRun (queryDesc=0x1b796e8, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:308
308 }
(gdb)
PortalRunSelect (portal=0x1af2468, forward=true, count=0, dest=0x1b74668) at pquery.c:934
934 nprocessed = queryDesc->estate->es_processed;
快照出栈,修改状态atStart/atEnd等
(gdb) n
935 PopActiveSnapshot();
(gdb)
938 if (!ScanDirectionIsNoMovement(direction))
(gdb)
940 if (nprocessed > 0)
(gdb) p nprocessed
$6 = 99991
(gdb) n
941 portal->atStart = false; /* OK to go backward now */
(gdb)
942 if (count == 0 || nprocessed < (uint64) count)
(gdb)
完成调用
(gdb) n
943 portal->atEnd = true; /* we retrieved 'em all */
(gdb) p count
$7 = 0
(gdb) n
944 portal->portalPos += nprocessed;
(gdb)
997 return nprocessed;
(gdb)
998 }
(gdb) n
PortalRun (portal=0x1af2468, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x1b74668, altdest=0x1b74668,
completionTag=0x7ffc5ff58740 "") at pquery.c:780
780 if (completionTag && portal->commandTag)
(gdb) p nprocessed
$8 = 99991
DONE!
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