/* ----------------------------------------------------------------
* ExecGatherMerge(node)
*
* Scans the relation via multiple workers and returns
* the next qualifying tuple.
* ----------------------------------------------------------------
*/
static TupleTableSlot *
ExecGatherMerge(PlanState *pstate)
{
GatherMergeState *node = castNode(GatherMergeState, pstate);
TupleTableSlot *slot;
ExprContext *econtext;
CHECK_FOR_INTERRUPTS();
/*
* As with Gather, we don't launch workers until this node is actually
* executed.
*/
if (!node->initialized)
{
EState *estate = node->ps.state;
GatherMerge *gm = castNode(GatherMerge, 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 (gm->num_workers > 0 && estate->es_use_parallel_mode)
{
ParallelContext *pcxt;
/* Initialize, or re-initialize, shared state needed by workers. */
if (!node->pei)
node->pei = ExecInitParallelPlan(node->ps.lefttree,
estate,
gm->initParam,
gm->num_workers,
node->tuples_needed);
else
ExecParallelReinitialize(node->ps.lefttree,
node->pei,
gm->initParam);
/* Try to launch workers. */
pcxt = node->pei->pcxt;
LaunchParallelWorkers(pcxt);
/* We save # workers launched for the benefit of EXPLAIN */
node->nworkers_launched = pcxt->nworkers_launched;
/* Set up tuple queue readers to read the results. */
if (pcxt->nworkers_launched > 0)
{
ExecParallelCreateReaders(node->pei);
/* Make a working array showing the active readers */
node->nreaders = pcxt->nworkers_launched;
node->reader = (TupleQueueReader **)
palloc(node->nreaders * sizeof(TupleQueueReader *));
memcpy(node->reader, node->pei->reader,
node->nreaders * sizeof(TupleQueueReader *));
}
else
{
/* No workers? Then never mind. */
node->nreaders = 0;
node->reader = NULL;
}
}
/* allow leader to participate if enabled or no choice */
if (parallel_leader_participation || node->nreaders == 0)
node->need_to_scan_locally = true;
node->initialized = true;
}
/*
* Reset per-tuple memory context to free any expression evaluation
* storage allocated in the previous tuple cycle.
*/
econtext = node->ps.ps_ExprContext;
ResetExprContext(econtext);
/*
* Get next tuple, either from one of our workers, or by running the plan
* ourselves.
*/
slot = gather_merge_getnext(node);
if (TupIsNull(slot))
return NULL;
/* If no projection is required, we're done. */
if (node->ps.ps_ProjInfo == NULL)
return slot;
/*
* Form the result tuple using ExecProject(), and return it.
*/
econtext->ecxt_outertuple = slot;
return ExecProject(node->ps.ps_ProjInfo);
}
/* ----------------------------------------------------------------
* ExecGather(node)
*
* Scans the relation via multiple workers and returns
* the next qualifying tuple.
* ----------------------------------------------------------------
*/
static TupleTableSlot *
ExecGather(PlanState *pstate)
{
GatherState *node = castNode(GatherState, pstate);
TupleTableSlot *slot;
ExprContext *econtext;
CHECK_FOR_INTERRUPTS();
/*
* 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 a large dynamic segment, so it is better to do it
* only 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 && estate->es_use_parallel_mode)
{
ParallelContext *pcxt;
/* Initialize, or re-initialize, shared state needed by workers. */
if (!node->pei)
node->pei = ExecInitParallelPlan(node->ps.lefttree,
estate,
gather->initParam,
gather->num_workers,
node->tuples_needed);
else
ExecParallelReinitialize(node->ps.lefttree,
node->pei,
gather->initParam);
/*
* Register backend workers. We might not get as many as we
* requested, or indeed any at all.
*/
pcxt = node->pei->pcxt;
LaunchParallelWorkers(pcxt);
/* We save # workers launched for the benefit of EXPLAIN */
node->nworkers_launched = pcxt->nworkers_launched;
/* Set up tuple queue readers to read the results. */
if (pcxt->nworkers_launched > 0)
{
ExecParallelCreateReaders(node->pei);
/* Make a working array showing the active readers */
node->nreaders = pcxt->nworkers_launched;
node->reader = (TupleQueueReader **)
palloc(node->nreaders * sizeof(TupleQueueReader *));
memcpy(node->reader, node->pei->reader,
node->nreaders * sizeof(TupleQueueReader *));
}
else
{
/* No workers? Then never mind. */
node->nreaders = 0;
node->reader = NULL;
}
node->nextreader = 0;
}
/* Run plan locally if no workers or enabled and not single-copy. */
node->need_to_scan_locally = (node->nreaders == 0)
|| (!gather->single_copy && parallel_leader_participation);
node->initialized = true;
}
/*
* Reset per-tuple memory context to free any expression evaluation
* storage allocated in the previous tuple cycle.
*/
econtext = node->ps.ps_ExprContext;
ResetExprContext(econtext);
/*
* Get next tuple, either from one of our workers, or by running the plan
* ourselves.
*/
slot = gather_getnext(node);
if (TupIsNull(slot))
return NULL;
/* If no projection is required, we're done. */
if (node->ps.ps_ProjInfo == NULL)
return slot;
/*
* Form the result tuple using ExecProject(), and return it.
*/
econtext->ecxt_outertuple = slot;
return ExecProject(node->ps.ps_ProjInfo);
}
