* tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
* or set scan->rs_ctup.t_data = NULL if no more tuples.
*
- * dir == NoMovementScanDirection means "re-fetch the tuple indicated
- * by scan->rs_ctup".
- *
* Note: the reason nkeys/key are passed separately, even though they are
* kept in the scan descriptor, is that the caller may not want us to check
* the scankeys.
linesleft = lines - lineoff + 1;
}
- else if (backward)
+ else
{
/* backward parallel scan not supported */
Assert(scan->rs_base.rs_parallel == NULL);
linesleft = lineoff;
}
- else
- {
- /*
- * ``no movement'' scan direction: refetch prior tuple
- */
- if (!scan->rs_inited)
- {
- Assert(!BufferIsValid(scan->rs_cbuf));
- tuple->t_data = NULL;
- return;
- }
-
- block = ItemPointerGetBlockNumber(&(tuple->t_self));
- if (block != scan->rs_cblock)
- heapgetpage((TableScanDesc) scan, block);
-
- /* Since the tuple was previously fetched, needn't lock page here */
- page = BufferGetPage(scan->rs_cbuf);
- TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
- lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
- lpp = PageGetItemId(page, lineoff);
- Assert(ItemIdIsNormal(lpp));
-
- tuple->t_data = (HeapTupleHeader) PageGetItem(page, lpp);
- tuple->t_len = ItemIdGetLength(lpp);
-
- return;
- }
/*
* advance the scan until we find a qualifying tuple or run out of stuff
linesleft = lines - lineindex;
}
- else if (backward)
+ else
{
/* backward parallel scan not supported */
Assert(scan->rs_base.rs_parallel == NULL);
linesleft = lineindex + 1;
}
- else
- {
- /*
- * ``no movement'' scan direction: refetch prior tuple
- */
- if (!scan->rs_inited)
- {
- Assert(!BufferIsValid(scan->rs_cbuf));
- tuple->t_data = NULL;
- return;
- }
-
- block = ItemPointerGetBlockNumber(&(tuple->t_self));
- if (block != scan->rs_cblock)
- heapgetpage((TableScanDesc) scan, block);
-
- /* Since the tuple was previously fetched, needn't lock page here */
- page = BufferGetPage(scan->rs_cbuf);
- TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
- lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
- lpp = PageGetItemId(page, lineoff);
- Assert(ItemIdIsNormal(lpp));
-
- tuple->t_data = (HeapTupleHeader) PageGetItem(page, lpp);
- tuple->t_len = ItemIdGetLength(lpp);
-
- /* check that rs_cindex is in sync */
- Assert(scan->rs_cindex < scan->rs_ntuples);
- Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);
-
- return;
- }
/*
* advance the scan until we find a qualifying tuple or run out of stuff
case BackwardScanDirection:
scandir = "Backward";
break;
- case NoMovementScanDirection:
- scandir = "NoMovement";
- break;
case ForwardScanDirection:
scandir = "Forward";
break;
* extract necessary information from index scan node
*/
estate = node->ss.ps.state;
- direction = estate->es_direction;
- /* flip direction if this is an overall backward scan */
- if (ScanDirectionIsBackward(((IndexOnlyScan *) node->ss.ps.plan)->indexorderdir))
- {
- if (ScanDirectionIsForward(direction))
- direction = BackwardScanDirection;
- else if (ScanDirectionIsBackward(direction))
- direction = ForwardScanDirection;
- }
+
+ /*
+ * Determine which direction to scan the index in based on the plan's scan
+ * direction and the current direction of execution.
+ */
+ direction = ScanDirectionCombine(estate->es_direction,
+ ((IndexOnlyScan *) node->ss.ps.plan)->indexorderdir);
scandesc = node->ioss_ScanDesc;
econtext = node->ss.ps.ps_ExprContext;
slot = node->ss.ss_ScanTupleSlot;
* extract necessary information from index scan node
*/
estate = node->ss.ps.state;
- direction = estate->es_direction;
- /* flip direction if this is an overall backward scan */
- if (ScanDirectionIsBackward(((IndexScan *) node->ss.ps.plan)->indexorderdir))
- {
- if (ScanDirectionIsForward(direction))
- direction = BackwardScanDirection;
- else if (ScanDirectionIsBackward(direction))
- direction = ForwardScanDirection;
- }
+
+ /*
+ * Determine which direction to scan the index in based on the plan's scan
+ * direction and the current direction of execution.
+ */
+ direction = ScanDirectionCombine(estate->es_direction,
+ ((IndexScan *) node->ss.ps.plan)->indexorderdir);
scandesc = node->iss_ScanDesc;
econtext = node->ss.ps.ps_ExprContext;
slot = node->ss.ss_ScanTupleSlot;
orderbyclauses,
orderbyclausecols,
useful_pathkeys,
- index_is_ordered ?
- ForwardScanDirection :
- NoMovementScanDirection,
+ ForwardScanDirection,
index_only_scan,
outer_relids,
loop_count,
orderbyclauses,
orderbyclausecols,
useful_pathkeys,
- index_is_ordered ?
- ForwardScanDirection :
- NoMovementScanDirection,
+ ForwardScanDirection,
index_only_scan,
outer_relids,
loop_count,
/* it should be a base rel... */
Assert(baserelid > 0);
Assert(best_path->path.parent->rtekind == RTE_RELATION);
+ /* check the scan direction is valid */
+ Assert(best_path->indexscandir == ForwardScanDirection ||
+ best_path->indexscandir == BackwardScanDirection);
/*
* Extract the index qual expressions (stripped of RestrictInfos) from the
* 'indexorderbycols' is an integer list of index column numbers (zero based)
* the ordering operators can be used with.
* 'pathkeys' describes the ordering of the path.
- * 'indexscandir' is ForwardScanDirection or BackwardScanDirection
- * for an ordered index, or NoMovementScanDirection for
- * an unordered index.
+ * 'indexscandir' is either ForwardScanDirection or BackwardScanDirection.
* 'indexonly' is true if an index-only scan is wanted.
* 'required_outer' is the set of outer relids for a parameterized path.
* 'loop_count' is the number of repetitions of the indexscan to factor into
/*
- * ScanDirection was an int8 for no apparent reason. I kept the original
- * values because I'm not sure if I'll break anything otherwise. -ay 2/95
+ * Defines the direction for scanning a table or an index. Scans are never
+ * invoked using NoMovementScanDirectionScans. For convenience, we use the
+ * values -1 and 1 for backward and forward scans. This allows us to perform
+ * a few mathematical tricks such as what is done in ScanDirectionCombine.
*/
typedef enum ScanDirection
{
ForwardScanDirection = 1
} ScanDirection;
+/*
+ * Determine the net effect of two direction specifications.
+ * This relies on having ForwardScanDirection = +1, BackwardScanDirection = -1,
+ * and will probably not do what you want if applied to any other values.
+ */
+#define ScanDirectionCombine(a, b) ((a) * (b))
+
/*
* ScanDirectionIsValid
* True iff scan direction is valid.
{
slot->tts_tableOid = RelationGetRelid(sscan->rs_rd);
+ /* We don't expect actual scans using NoMovementScanDirection */
+ Assert(direction == ForwardScanDirection ||
+ direction == BackwardScanDirection);
+
/*
* We don't expect direct calls to table_scan_getnextslot with valid
* CheckXidAlive for catalog or regular tables. See detailed comments in
/* Ensure table_beginscan_tidrange() was used. */
Assert((sscan->rs_flags & SO_TYPE_TIDRANGESCAN) != 0);
+ /* We don't expect actual scans using NoMovementScanDirection */
+ Assert(direction == ForwardScanDirection ||
+ direction == BackwardScanDirection);
+
return sscan->rs_rd->rd_tableam->scan_getnextslot_tidrange(sscan,
direction,
slot);
* on which index column each ORDER BY can be used with.)
*
* 'indexscandir' is one of:
- * ForwardScanDirection: forward scan of an ordered index
+ * ForwardScanDirection: forward scan of an index
* BackwardScanDirection: backward scan of an ordered index
- * NoMovementScanDirection: scan of an unordered index, or don't care
- * (The executor doesn't care whether it gets ForwardScanDirection or
- * NoMovementScanDirection for an indexscan, but the planner wants to
- * distinguish ordered from unordered indexes for building pathkeys.)
+ * Unordered indexes will always have an indexscandir of ForwardScanDirection.
*
* 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
* we need not recompute them when considering using the same index in a
projects / users / rhaas / postgres.git / commitdiff