/* ----------------------------------------------------------------
* ExecEndGather
*
* frees any storage allocated through C routines.
* ----------------------------------------------------------------
*/
void
ExecEndGather(GatherState *node)
{
ExecShutdownGather(node);
ExecFreeExprContext(&node->ps);
ExecClearTuple(node->ps.ps_ResultTupleSlot);
ExecEndNode(outerPlanState(node));
}
/* ----------------------------------------------------------------
* ExecGather(node)
*
* Scans the relation via multiple workers and returns
* the next qualifying tuple.
* ----------------------------------------------------------------
*/
TupleTableSlot *
ExecGather(GatherState *node)
{
TupleTableSlot *fslot = node->funnel_slot;
int i;
TupleTableSlot *slot;
TupleTableSlot *resultSlot;
ExprDoneCond isDone;
ExprContext *econtext;
/*
* Initialize the parallel context and workers on first execution. We do
* this on first execution rather than during node initialization, as it
* needs to allocate large dynamic segement, so it is better to do if it
* is really needed.
*/
if (!node->initialized)
{
EState *estate = node->ps.state;
Gather *gather = (Gather *) node->ps.plan;
/*
* Sometimes we might have to run without parallelism; but if
* parallel mode is active then we can try to fire up some workers.
*/
if (gather->num_workers > 0 && IsInParallelMode())
{
ParallelContext *pcxt;
bool got_any_worker = false;
/* Initialize the workers required to execute Gather node. */
if (!node->pei)
node->pei = ExecInitParallelPlan(node->ps.lefttree,
estate,
gather->num_workers);
/*
* Register backend workers. We might not get as many as we
* requested, or indeed any at all.
*/
pcxt = node->pei->pcxt;
LaunchParallelWorkers(pcxt);
/* Set up tuple queue readers to read the results. */
if (pcxt->nworkers > 0)
{
node->nreaders = 0;
node->reader =
palloc(pcxt->nworkers * sizeof(TupleQueueReader *));
for (i = 0; i < pcxt->nworkers; ++i)
{
if (pcxt->worker[i].bgwhandle == NULL)
continue;
shm_mq_set_handle(node->pei->tqueue[i],
pcxt->worker[i].bgwhandle);
node->reader[node->nreaders++] =
CreateTupleQueueReader(node->pei->tqueue[i],
fslot->tts_tupleDescriptor);
got_any_worker = true;
}
}
/* No workers? Then never mind. */
if (!got_any_worker)
ExecShutdownGather(node);
}
/* Run plan locally if no workers or not single-copy. */
node->need_to_scan_locally = (node->reader == NULL)
|| !gather->single_copy;
node->initialized = true;
}
/*
* Check to see if we're still projecting out tuples from a previous scan
* tuple (because there is a function-returning-set in the projection
* expressions). If so, try to project another one.
*/
if (node->ps.ps_TupFromTlist)
{
resultSlot = ExecProject(node->ps.ps_ProjInfo, &isDone);
if (isDone == ExprMultipleResult)
return resultSlot;
/* Done with that source tuple... */
node->ps.ps_TupFromTlist = false;
}
/*
* Reset per-tuple memory context to free any expression evaluation
* storage allocated in the previous tuple cycle. Note we can't do this
* until we're done projecting.
*/
econtext = node->ps.ps_ExprContext;
ResetExprContext(econtext);
/* Get and return the next tuple, projecting if necessary. */
for (;;)
{
/*
* Get next tuple, either from one of our workers, or by running the
* plan ourselves.
*/
slot = gather_getnext(node);
if (TupIsNull(slot))
return NULL;
/*
* form the result tuple using ExecProject(), and return it --- unless
* the projection produces an empty set, in which case we must loop
* back around for another tuple
*/
econtext->ecxt_outertuple = slot;
resultSlot = ExecProject(node->ps.ps_ProjInfo, &isDone);
if (isDone != ExprEndResult)
{
node->ps.ps_TupFromTlist = (isDone == ExprMultipleResult);
return resultSlot;
}
}
return slot;
}
