/* ----------------------------------------------------------------
* ExecInitCteScan
* ----------------------------------------------------------------
*/
CteScanState *
ExecInitCteScan(CteScan *node, EState *estate, int eflags)
{
CteScanState *scanstate;
ParamExecData *prmdata;
/* check for unsupported flags */
Assert(!(eflags & EXEC_FLAG_MARK));
/*
* For the moment we have to force the tuplestore to allow REWIND, because
* we might be asked to rescan the CTE even though upper levels didn't
* tell us to be prepared to do it efficiently. Annoying, since this
* prevents truncation of the tuplestore. XXX FIXME
*
* Note: if we are in an EPQ recheck plan tree, it's likely that no access
* to the tuplestore is needed at all, making this even more annoying.
* It's not worth improving that as long as all the read pointers would
* have REWIND anyway, but if we ever improve this logic then that aspect
* should be considered too.
*/
eflags |= EXEC_FLAG_REWIND;
/*
* CteScan should not have any children.
*/
Assert(outerPlan(node) == NULL);
Assert(innerPlan(node) == NULL);
/*
* create new CteScanState for node
*/
scanstate = makeNode(CteScanState);
scanstate->ss.ps.plan = (Plan *) node;
scanstate->ss.ps.state = estate;
scanstate->eflags = eflags;
scanstate->cte_table = NULL;
scanstate->eof_cte = false;
/*
* Find the already-initialized plan for the CTE query.
*/
scanstate->cteplanstate = (PlanState *) list_nth(estate->es_subplanstates,
node->ctePlanId - 1);
/*
* The Param slot associated with the CTE query is used to hold a pointer
* to the CteState of the first CteScan node that initializes for this
* CTE. This node will be the one that holds the shared state for all the
* CTEs, particularly the shared tuplestore.
*/
prmdata = &(estate->es_param_exec_vals[node->cteParam]);
Assert(prmdata->execPlan == NULL);
Assert(!prmdata->isnull);
scanstate->leader = (CteScanState *) DatumGetPointer(prmdata->value);
if (scanstate->leader == NULL)
{
/* I am the leader */
prmdata->value = PointerGetDatum(scanstate);
scanstate->leader = scanstate;
scanstate->cte_table = tuplestore_begin_heap(true, false, work_mem);
tuplestore_set_eflags(scanstate->cte_table, scanstate->eflags);
scanstate->readptr = 0;
}
else
{
/* Not the leader */
Assert(IsA(scanstate->leader, CteScanState));
/* Create my own read pointer, and ensure it is at start */
scanstate->readptr =
tuplestore_alloc_read_pointer(scanstate->leader->cte_table,
scanstate->eflags);
tuplestore_select_read_pointer(scanstate->leader->cte_table,
scanstate->readptr);
tuplestore_rescan(scanstate->leader->cte_table);
}
/*
* Miscellaneous initialization
*
* create expression context for node
*/
ExecAssignExprContext(estate, &scanstate->ss.ps);
/*
* initialize child expressions
*/
scanstate->ss.ps.targetlist = (List *)
ExecInitExpr((Expr *) node->scan.plan.targetlist,
(PlanState *) scanstate);
scanstate->ss.ps.qual = (List *)
ExecInitExpr((Expr *) node->scan.plan.qual,
(PlanState *) scanstate);
/*
* tuple table initialization
*/
ExecInitResultTupleSlot(estate, &scanstate->ss.ps);
ExecInitScanTupleSlot(estate, &scanstate->ss);
/*
* The scan tuple type (ie, the rowtype we expect to find in the work
* table) is the same as the result rowtype of the CTE query.
*/
ExecAssignScanType(&scanstate->ss,
ExecGetResultType(scanstate->cteplanstate));
/*
* Initialize result tuple type and projection info.
*/
ExecAssignResultTypeFromTL(&scanstate->ss.ps);
ExecAssignScanProjectionInfo(&scanstate->ss);
return scanstate;
}
/* ----------------------------------------------------------------
* ExecMaterial
*
* As long as we are at the end of the data collected in the tuplestore,
* we collect one new row from the subplan on each call, and stash it
* aside in the tuplestore before returning it. The tuplestore is
* only read if we are asked to scan backwards, rescan, or mark/restore.
*
* ----------------------------------------------------------------
*/
TupleTableSlot * /* result tuple from subplan */
ExecMaterial(MaterialState *node)
{
EState *estate;
ScanDirection dir;
bool forward;
Tuplestorestate *tuplestorestate;
bool eof_tuplestore;
TupleTableSlot *slot;
/*
* get state info from node
*/
estate = node->ss.ps.state;
dir = estate->es_direction;
forward = ScanDirectionIsForward(dir);
tuplestorestate = node->tuplestorestate;
/*
* If first time through, and we need a tuplestore, initialize it.
*/
if (tuplestorestate == NULL && node->eflags != 0)
{
tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
tuplestore_set_eflags(tuplestorestate, node->eflags);
if (node->eflags & EXEC_FLAG_MARK)
{
/*
* Allocate a second read pointer to serve as the mark. We know it
* must have index 1, so needn't store that.
*/
int ptrno PG_USED_FOR_ASSERTS_ONLY;
ptrno = tuplestore_alloc_read_pointer(tuplestorestate,
node->eflags);
Assert(ptrno == 1);
}
node->tuplestorestate = tuplestorestate;
}
/*
* If we are not at the end of the tuplestore, or are going backwards, try
* to fetch a tuple from tuplestore.
*/
eof_tuplestore = (tuplestorestate == NULL) ||
tuplestore_ateof(tuplestorestate);
if (!forward && eof_tuplestore)
{
if (!node->eof_underlying)
{
/*
* When reversing direction at tuplestore EOF, the first
* gettupleslot call will fetch the last-added tuple; but we want
* to return the one before that, if possible. So do an extra
* fetch.
*/
if (!tuplestore_advance(tuplestorestate, forward))
return NULL; /* the tuplestore must be empty */
}
eof_tuplestore = false;
}
/*
* If we can fetch another tuple from the tuplestore, return it.
*/
slot = node->ss.ps.ps_ResultTupleSlot;
if (!eof_tuplestore)
{
if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
return slot;
if (forward)
eof_tuplestore = true;
}
/*
* If necessary, try to fetch another row from the subplan.
*
* Note: the eof_underlying state variable exists to short-circuit further
* subplan calls. It's not optional, unfortunately, because some plan
* node types are not robust about being called again when they've already
* returned NULL.
*/
if (eof_tuplestore && !node->eof_underlying)
{
PlanState *outerNode;
TupleTableSlot *outerslot;
/*
* We can only get here with forward==true, so no need to worry about
* which direction the subplan will go.
*/
outerNode = outerPlanState(node);
outerslot = ExecProcNode(outerNode);
if (TupIsNull(outerslot))
{
node->eof_underlying = true;
return NULL;
}
/*
* Append a copy of the returned tuple to tuplestore. NOTE: because
* the tuplestore is certainly in EOF state, its read position will
* move forward over the added tuple. This is what we want.
*/
if (tuplestorestate)
tuplestore_puttupleslot(tuplestorestate, outerslot);
/*
* We can just return the subplan's returned tuple, without copying.
*/
return outerslot;
}
/*
* Nothing left ...
*/
return ExecClearTuple(slot);
}
