scan->rs_ntuples = ntup;
}
+/*
+ * heapgettup_initial_block - return the first BlockNumber to scan
+ *
+ * Returns InvalidBlockNumber when there are no blocks to scan. This can
+ * occur with empty tables and in parallel scans when parallel workers get all
+ * of the pages before we can get a chance to get our first page.
+ */
+static BlockNumber
+heapgettup_initial_block(HeapScanDesc scan, ScanDirection dir)
+{
+ Assert(!scan->rs_inited);
+
+ /* When there are no pages to scan, return InvalidBlockNumber */
+ if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+ return InvalidBlockNumber;
+
+ if (ScanDirectionIsForward(dir))
+ {
+ /* serial scan */
+ if (scan->rs_base.rs_parallel == NULL)
+ return scan->rs_startblock;
+ else
+ {
+ /* parallel scan */
+ table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
+ scan->rs_parallelworkerdata,
+ (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel);
+
+ /* may return InvalidBlockNumber if there are no more blocks */
+ return table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
+ scan->rs_parallelworkerdata,
+ (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel);
+ }
+ }
+ else
+ {
+ /* backward parallel scan not supported */
+ Assert(scan->rs_base.rs_parallel == NULL);
+
+ /*
+ * Disable reporting to syncscan logic in a backwards scan; it's not
+ * very likely anyone else is doing the same thing at the same time,
+ * and much more likely that we'll just bollix things for forward
+ * scanners.
+ */
+ scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
+
+ /*
+ * Start from last page of the scan. Ensure we take into account
+ * rs_numblocks if it's been adjusted by heap_setscanlimits().
+ */
+ if (scan->rs_numblocks != InvalidBlockNumber)
+ return (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
+
+ if (scan->rs_startblock > 0)
+ return scan->rs_startblock - 1;
+
+ return scan->rs_nblocks - 1;
+ }
+}
+
/* ----------------
* heapgettup - fetch next heap tuple
*
{
if (!scan->rs_inited)
{
+ block = heapgettup_initial_block(scan, dir);
+
/*
- * return null immediately if relation is empty
+ * Check if we have reached the end of the scan already. This
+ * could happen if the table is empty or if the parallel workers
+ * have already finished the scan before we did anything ourselves
*/
- if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+ if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
- if (scan->rs_base.rs_parallel != NULL)
- {
- ParallelBlockTableScanDesc pbscan =
- (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
- ParallelBlockTableScanWorker pbscanwork =
- scan->rs_parallelworkerdata;
-
- table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
- pbscanwork, pbscan);
-
- block = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
- pbscanwork, pbscan);
-
- /* Other processes might have already finished the scan. */
- if (block == InvalidBlockNumber)
- {
- Assert(!BufferIsValid(scan->rs_cbuf));
- tuple->t_data = NULL;
- return;
- }
- }
- else
- block = scan->rs_startblock; /* first page */
heapgetpage((TableScanDesc) scan, block);
lineoff = FirstOffsetNumber; /* first offnum */
scan->rs_inited = true;
}
else
{
- /* backward parallel scan not supported */
- Assert(scan->rs_base.rs_parallel == NULL);
-
if (!scan->rs_inited)
{
+ block = heapgettup_initial_block(scan, dir);
+
/*
- * return null immediately if relation is empty
+ * Check if we have reached the end of the scan already. This
+ * could happen if the table is empty.
*/
- if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+ if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
- /*
- * Disable reporting to syncscan logic in a backwards scan; it's
- * not very likely anyone else is doing the same thing at the same
- * time, and much more likely that we'll just bollix things for
- * forward scanners.
- */
- scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
-
- /*
- * Start from last page of the scan. Ensure we take into account
- * rs_numblocks if it's been adjusted by heap_setscanlimits().
- */
- if (scan->rs_numblocks != InvalidBlockNumber)
- block = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
- else if (scan->rs_startblock > 0)
- block = scan->rs_startblock - 1;
- else
- block = scan->rs_nblocks - 1;
heapgetpage((TableScanDesc) scan, block);
+ LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
+
+ page = BufferGetPage(scan->rs_cbuf);
+ TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
+ lines = PageGetMaxOffsetNumber(page);
+ lineoff = lines; /* final offnum */
+ scan->rs_inited = true;
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
- }
+ LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
- LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
+ page = BufferGetPage(scan->rs_cbuf);
+ TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
+ lines = PageGetMaxOffsetNumber(page);
- page = BufferGetPage(scan->rs_cbuf);
- TestForOldSnapshot(snapshot, scan->rs_base.rs_rd, page);
- lines = PageGetMaxOffsetNumber(page);
-
- if (!scan->rs_inited)
- {
- lineoff = lines; /* final offnum */
- scan->rs_inited = true;
- }
- else
- {
/*
* The previous returned tuple may have been vacuumed since the
* previous scan when we use a non-MVCC snapshot, so we must
{
if (!scan->rs_inited)
{
+ block = heapgettup_initial_block(scan, dir);
+
/*
- * return null immediately if relation is empty
+ * Check if we have reached the end of the scan already. This
+ * could happen if the table is empty or if the parallel workers
+ * have already finished the scan before we did anything ourselves
*/
- if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+ if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
- if (scan->rs_base.rs_parallel != NULL)
- {
- ParallelBlockTableScanDesc pbscan =
- (ParallelBlockTableScanDesc) scan->rs_base.rs_parallel;
- ParallelBlockTableScanWorker pbscanwork =
- scan->rs_parallelworkerdata;
-
- table_block_parallelscan_startblock_init(scan->rs_base.rs_rd,
- pbscanwork, pbscan);
-
- block = table_block_parallelscan_nextpage(scan->rs_base.rs_rd,
- pbscanwork, pbscan);
-
- /* Other processes might have already finished the scan. */
- if (block == InvalidBlockNumber)
- {
- Assert(!BufferIsValid(scan->rs_cbuf));
- tuple->t_data = NULL;
- return;
- }
- }
- else
- block = scan->rs_startblock; /* first page */
heapgetpage((TableScanDesc) scan, block);
lineindex = 0;
scan->rs_inited = true;
}
else
{
- /* backward parallel scan not supported */
- Assert(scan->rs_base.rs_parallel == NULL);
-
if (!scan->rs_inited)
{
+ block = heapgettup_initial_block(scan, dir);
+
/*
- * return null immediately if relation is empty
+ * Check if we have reached the end of the scan already. This
+ * could happen if the table is empty.
*/
- if (scan->rs_nblocks == 0 || scan->rs_numblocks == 0)
+ if (block == InvalidBlockNumber)
{
Assert(!BufferIsValid(scan->rs_cbuf));
tuple->t_data = NULL;
return;
}
- /*
- * Disable reporting to syncscan logic in a backwards scan; it's
- * not very likely anyone else is doing the same thing at the same
- * time, and much more likely that we'll just bollix things for
- * forward scanners.
- */
- scan->rs_base.rs_flags &= ~SO_ALLOW_SYNC;
-
- /*
- * Start from last page of the scan. Ensure we take into account
- * rs_numblocks if it's been adjusted by heap_setscanlimits().
- */
- if (scan->rs_numblocks != InvalidBlockNumber)
- block = (scan->rs_startblock + scan->rs_numblocks - 1) % scan->rs_nblocks;
- else if (scan->rs_startblock > 0)
- block = scan->rs_startblock - 1;
- else
- block = scan->rs_nblocks - 1;
heapgetpage((TableScanDesc) scan, block);
+ page = BufferGetPage(scan->rs_cbuf);
+ TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
+ lines = scan->rs_ntuples;
+ lineindex = lines - 1;
+ scan->rs_inited = true;
}
else
{
/* continue from previously returned page/tuple */
block = scan->rs_cblock; /* current page */
- }
-
- page = BufferGetPage(scan->rs_cbuf);
- TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
- lines = scan->rs_ntuples;
- if (!scan->rs_inited)
- {
- lineindex = lines - 1;
- scan->rs_inited = true;
- }
- else
- {
+ page = BufferGetPage(scan->rs_cbuf);
+ TestForOldSnapshot(scan->rs_base.rs_snapshot, scan->rs_base.rs_rd, page);
+ lines = scan->rs_ntuples;
lineindex = scan->rs_cindex - 1;
}
/* block and lineindex now reference the previous visible tid */
projects / users / c2main / postgres.git / commitdiff