Teach SPGiST to store nulls and do whole-index scans.

This patch fixes the other major compatibility-breaking limitation of
SPGiST, that it didn't store anything for null values of the indexed
column, and so could not support whole-index scans or "x IS NULL"
tests.  The approach is to create a wholly separate search tree for
the null entries, and use fixed "allTheSame" insertion and search
rules when processing this tree, instead of calling the index opclass
methods.  This way the opclass methods do not need to worry about
dealing with nulls.

Catversion bump is for pg_am updates as well as the change in on-disk
format of SPGiST indexes; there are some tweaks in SPGiST WAL records
as well.

Heavily rewritten version of a patch by Oleg Bartunov and Teodor Sigaev.
(The original also stored nulls separately, but it reused GIN code to do
so; which required undesirable compromises in the on-disk format, and
would likely lead to bugs due to the GIN code being required to work in
two very different contexts.)

1 files changed, 27 insertions, 10 deletions

diff --git a/src/backend/access/spgist/spgxlog.c b/src/backend/access/spgist/spgxlog.c
index daa8ae300ba..8e87e2adc90 100644
--- a/src/backend/access/spgist/spgxlog.c
+++ b/src/backend/access/spgist/spgxlog.c
@@ -84,7 +84,7 @@ spgRedoCreateIndex(XLogRecPtr lsn, XLogRecord *record)
 	MarkBufferDirty(buffer);
 	UnlockReleaseBuffer(buffer);
 
-	buffer = XLogReadBuffer(*node, SPGIST_HEAD_BLKNO, true);
+	buffer = XLogReadBuffer(*node, SPGIST_ROOT_BLKNO, true);
 	Assert(BufferIsValid(buffer));
 	SpGistInitBuffer(buffer, SPGIST_LEAF);
 	page = (Page) BufferGetPage(buffer);
@@ -92,6 +92,15 @@ spgRedoCreateIndex(XLogRecPtr lsn, XLogRecord *record)
 	PageSetTLI(page, ThisTimeLineID);
 	MarkBufferDirty(buffer);
 	UnlockReleaseBuffer(buffer);
+
+	buffer = XLogReadBuffer(*node, SPGIST_NULL_BLKNO, true);
+	Assert(BufferIsValid(buffer));
+	SpGistInitBuffer(buffer, SPGIST_LEAF | SPGIST_NULLS);
+	page = (Page) BufferGetPage(buffer);
+	PageSetLSN(page, lsn);
+	PageSetTLI(page, ThisTimeLineID);
+	MarkBufferDirty(buffer);
+	UnlockReleaseBuffer(buffer);
 }
 
 static void
@@ -116,7 +125,8 @@ spgRedoAddLeaf(XLogRecPtr lsn, XLogRecord *record)
 			page = BufferGetPage(buffer);
 
 			if (xldata->newPage)
-				SpGistInitBuffer(buffer, SPGIST_LEAF);
+				SpGistInitBuffer(buffer,
+								 SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
 
 			if (!XLByteLE(lsn, PageGetLSN(page)))
 			{
@@ -218,7 +228,8 @@ spgRedoMoveLeafs(XLogRecPtr lsn, XLogRecord *record)
 			page = BufferGetPage(buffer);
 
 			if (xldata->newPage)
-				SpGistInitBuffer(buffer, SPGIST_LEAF);
+				SpGistInitBuffer(buffer,
+								 SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
 
 			if (!XLByteLE(lsn, PageGetLSN(page)))
 			{
@@ -344,6 +355,7 @@ spgRedoAddNode(XLogRecPtr lsn, XLogRecord *record)
 			{
 				page = BufferGetPage(buffer);
 
+				/* AddNode is not used for nulls pages */
 				if (xldata->newPage)
 					SpGistInitBuffer(buffer, 0);
 
@@ -464,6 +476,7 @@ spgRedoSplitTuple(XLogRecPtr lsn, XLogRecord *record)
 		{
 			page = BufferGetPage(buffer);
 
+			/* SplitTuple is not used for nulls pages */
 			if (xldata->newPage)
 				SpGistInitBuffer(buffer, 0);
 
@@ -545,7 +558,7 @@ spgRedoPickSplit(XLogRecPtr lsn, XLogRecord *record)
 	 */
 	bbi = 0;
 
-	if (xldata->blknoSrc == SPGIST_HEAD_BLKNO)
+	if (SpGistBlockIsRoot(xldata->blknoSrc))
 	{
 		/* when splitting root, we touch it only in the guise of new inner */
 		srcBuffer = InvalidBuffer;
@@ -557,7 +570,8 @@ spgRedoPickSplit(XLogRecPtr lsn, XLogRecord *record)
 		Assert(BufferIsValid(srcBuffer));
 		page = (Page) BufferGetPage(srcBuffer);
 
-		SpGistInitBuffer(srcBuffer, SPGIST_LEAF);
+		SpGistInitBuffer(srcBuffer,
+						 SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
 		/* don't update LSN etc till we're done with it */
 	}
 	else
@@ -612,7 +626,8 @@ spgRedoPickSplit(XLogRecPtr lsn, XLogRecord *record)
 		Assert(BufferIsValid(destBuffer));
 		page = (Page) BufferGetPage(destBuffer);
 
-		SpGistInitBuffer(destBuffer, SPGIST_LEAF);
+		SpGistInitBuffer(destBuffer,
+						 SPGIST_LEAF | (xldata->storesNulls ? SPGIST_NULLS : 0));
 		/* don't update LSN etc till we're done with it */
 	}
 	else
@@ -678,7 +693,8 @@ spgRedoPickSplit(XLogRecPtr lsn, XLogRecord *record)
 			page = BufferGetPage(buffer);
 
 			if (xldata->initInner)
-				SpGistInitBuffer(buffer, 0);
+				SpGistInitBuffer(buffer,
+								 (xldata->storesNulls ? SPGIST_NULLS : 0));
 
 			if (!XLByteLE(lsn, PageGetLSN(page)))
 			{
@@ -709,7 +725,7 @@ spgRedoPickSplit(XLogRecPtr lsn, XLogRecord *record)
 	if (xldata->blknoParent == InvalidBlockNumber)
 	{
 		/* no parent cause we split the root */
-		Assert(xldata->blknoInner == SPGIST_HEAD_BLKNO);
+		Assert(SpGistBlockIsRoot(xldata->blknoInner));
 	}
 	else if (xldata->blknoInner != xldata->blknoParent)
 	{
@@ -842,7 +858,7 @@ spgRedoVacuumRoot(XLogRecPtr lsn, XLogRecord *record)
 
 	if (!(record->xl_info & XLR_BKP_BLOCK_1))
 	{
-		buffer = XLogReadBuffer(xldata->node, SPGIST_HEAD_BLKNO, false);
+		buffer = XLogReadBuffer(xldata->node, xldata->blkno, false);
 		if (BufferIsValid(buffer))
 		{
 			page = BufferGetPage(buffer);
@@ -1039,7 +1055,8 @@ spg_desc(StringInfo buf, uint8 xl_info, char *rec)
 			break;
 		case XLOG_SPGIST_VACUUM_ROOT:
 			out_target(buf, ((spgxlogVacuumRoot *) rec)->node);
-			appendStringInfo(buf, "vacuum leaf tuples on root page");
+			appendStringInfo(buf, "vacuum leaf tuples on root page %u",
+							 ((spgxlogVacuumRoot *) rec)->blkno);
 			break;
 		case XLOG_SPGIST_VACUUM_REDIRECT:
 			out_target(buf, ((spgxlogVacuumRedirect *) rec)->node);