Separate TBM[Shared|Private]Iterator and TBMIterateResult

Remove the TBMIterateResult member from the TBMPrivateIterator and
TBMSharedIterator and make tbm_[shared|private_]iterate() take a
TBMIterateResult as a parameter.

This allows tidbitmap API users to manage multiple TBMIterateResults per
scan. This is required for bitmap heap scan to use the read stream API,
with which there may be multiple I/Os in flight at once, each one with a
TBMIterateResult.

Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/d4bb26c9-fe07-439e-ac53-c0e244387e01%40vondra.me

3 files changed, 30 insertions, 33 deletions

diff --git a/src/backend/access/gin/ginget.c b/src/backend/access/gin/ginget.c
index 4a56f19390d..f29ccd3c2d1 100644
--- a/src/backend/access/gin/ginget.c
+++ b/src/backend/access/gin/ginget.c
@@ -332,8 +332,8 @@ restartScanEntry:
 	entry->list = NULL;
 	entry->nlist = 0;
 	entry->matchBitmap = NULL;
-	entry->matchResult = NULL;
 	entry->matchNtuples = -1;
+	entry->matchResult.blockno = InvalidBlockNumber;
 	entry->reduceResult = false;
 	entry->predictNumberResult = 0;
 
@@ -827,20 +827,19 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 		{
 			/*
 			 * If we've exhausted all items on this block, move to next block
-			 * in the bitmap.
+			 * in the bitmap. tbm_private_iterate() sets matchResult.blockno
+			 * to InvalidBlockNumber when the bitmap is exhausted.
 			 */
-			while (entry->matchResult == NULL ||
-				   (!entry->matchResult->lossy &&
+			while ((!BlockNumberIsValid(entry->matchResult.blockno)) ||
+				   (!entry->matchResult.lossy &&
 					entry->offset >= entry->matchNtuples) ||
-				   entry->matchResult->blockno < advancePastBlk ||
+				   entry->matchResult.blockno < advancePastBlk ||
 				   (ItemPointerIsLossyPage(&advancePast) &&
-					entry->matchResult->blockno == advancePastBlk))
+					entry->matchResult.blockno == advancePastBlk))
 			{
-				entry->matchResult =
-					tbm_private_iterate(entry->matchIterator);
-
-				if (entry->matchResult == NULL)
+				if (!tbm_private_iterate(entry->matchIterator, &entry->matchResult))
 				{
+					Assert(!BlockNumberIsValid(entry->matchResult.blockno));
 					ItemPointerSetInvalid(&entry->curItem);
 					tbm_end_private_iterate(entry->matchIterator);
 					entry->matchIterator = NULL;
@@ -849,14 +848,14 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 				}
 
 				/* Exact pages need their tuple offsets extracted. */
-				if (!entry->matchResult->lossy)
-					entry->matchNtuples = tbm_extract_page_tuple(entry->matchResult,
+				if (!entry->matchResult.lossy)
+					entry->matchNtuples = tbm_extract_page_tuple(&entry->matchResult,
 																 entry->matchOffsets,
 																 TBM_MAX_TUPLES_PER_PAGE);
 
 				/*
 				 * Reset counter to the beginning of entry->matchResult. Note:
-				 * entry->offset is still greater than entry->matchNtuples if
+				 * entry->offset is still greater than matchResult.ntuples if
 				 * matchResult is lossy.  So, on next call we will get next
 				 * result from TIDBitmap.
 				 */
@@ -869,10 +868,10 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 			 * We're now on the first page after advancePast which has any
 			 * items on it. If it's a lossy result, return that.
 			 */
-			if (entry->matchResult->lossy)
+			if (entry->matchResult.lossy)
 			{
 				ItemPointerSetLossyPage(&entry->curItem,
-										entry->matchResult->blockno);
+										entry->matchResult.blockno);
 
 				/*
 				 * We might as well fall out of the loop; we could not
@@ -889,7 +888,7 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 			Assert(entry->matchNtuples > -1);
 
 			/* Skip over any offsets <= advancePast, and return that. */
-			if (entry->matchResult->blockno == advancePastBlk)
+			if (entry->matchResult.blockno == advancePastBlk)
 			{
 				Assert(entry->matchNtuples > 0);
 
@@ -910,7 +909,7 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 			}
 
 			ItemPointerSet(&entry->curItem,
-						   entry->matchResult->blockno,
+						   entry->matchResult.blockno,
 						   entry->matchOffsets[entry->offset]);
 			entry->offset++;
 
diff --git a/src/backend/access/gin/ginscan.c b/src/backend/access/gin/ginscan.c
index f6cdd098a02..c2d1771bd77 100644
--- a/src/backend/access/gin/ginscan.c
+++ b/src/backend/access/gin/ginscan.c
@@ -111,7 +111,7 @@ ginFillScanEntry(GinScanOpaque so, OffsetNumber attnum,
 	ItemPointerSetMin(&scanEntry->curItem);
 	scanEntry->matchBitmap = NULL;
 	scanEntry->matchIterator = NULL;
-	scanEntry->matchResult = NULL;
+	scanEntry->matchResult.blockno = InvalidBlockNumber;
 	scanEntry->matchNtuples = -1;
 	scanEntry->list = NULL;
 	scanEntry->nlist = 0;
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index eecff8ffd67..25d26409e2c 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -2126,7 +2126,7 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 	Buffer		buffer;
 	Snapshot	snapshot;
 	int			ntup;
-	TBMIterateResult *tbmres;
+	TBMIterateResult tbmres;
 	OffsetNumber offsets[TBM_MAX_TUPLES_PER_PAGE];
 	int			noffsets = -1;
 
@@ -2142,14 +2142,12 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 	{
 		CHECK_FOR_INTERRUPTS();
 
-		tbmres = tbm_iterate(&scan->st.rs_tbmiterator);
-
-		if (tbmres == NULL)
+		if (!tbm_iterate(&scan->st.rs_tbmiterator, &tbmres))
 			return false;
 
 		/* Exact pages need their tuple offsets extracted. */
-		if (!tbmres->lossy)
-			noffsets = tbm_extract_page_tuple(tbmres, offsets,
+		if (!tbmres.lossy)
+			noffsets = tbm_extract_page_tuple(&tbmres, offsets,
 											  TBM_MAX_TUPLES_PER_PAGE);
 
 		/*
@@ -2161,11 +2159,11 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 		 * reachable by the index.
 		 */
 	} while (!IsolationIsSerializable() &&
-			 tbmres->blockno >= hscan->rs_nblocks);
+			 tbmres.blockno >= hscan->rs_nblocks);
 
 	/* Got a valid block */
-	*blockno = tbmres->blockno;
-	*recheck = tbmres->recheck;
+	*blockno = tbmres.blockno;
+	*recheck = tbmres.recheck;
 
 	/*
 	 * We can skip fetching the heap page if we don't need any fields from the
@@ -2173,11 +2171,11 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 	 * page are visible to our transaction.
 	 */
 	if (!(scan->rs_flags & SO_NEED_TUPLES) &&
-		!tbmres->recheck &&
-		VM_ALL_VISIBLE(scan->rs_rd, tbmres->blockno, &bscan->rs_vmbuffer))
+		!tbmres.recheck &&
+		VM_ALL_VISIBLE(scan->rs_rd, tbmres.blockno, &bscan->rs_vmbuffer))
 	{
 		/* can't be lossy in the skip_fetch case */
-		Assert(!tbmres->lossy);
+		Assert(!tbmres.lossy);
 		Assert(bscan->rs_empty_tuples_pending >= 0);
 		Assert(noffsets > -1);
 
@@ -2186,7 +2184,7 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 		return true;
 	}
 
-	block = tbmres->blockno;
+	block = tbmres.blockno;
 
 	/*
 	 * Acquire pin on the target heap page, trading in any pin we held before.
@@ -2215,7 +2213,7 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 	/*
 	 * We need two separate strategies for lossy and non-lossy cases.
 	 */
-	if (!tbmres->lossy)
+	if (!tbmres.lossy)
 	{
 		/*
 		 * Bitmap is non-lossy, so we just look through the offsets listed in
@@ -2279,7 +2277,7 @@ heapam_scan_bitmap_next_block(TableScanDesc scan,
 	Assert(ntup <= MaxHeapTuplesPerPage);
 	hscan->rs_ntuples = ntup;
 
-	if (tbmres->lossy)
+	if (tbmres.lossy)
 		(*lossy_pages)++;
 	else
 		(*exact_pages)++;