Misc GIN refactoring.

Merge the isEnoughSpace and placeToPage functions in the b-tree interface
into one function that tries to put a tuple on page, and returns false if
it doesn't fit.

Move createPostingTree function to gindatapage.c, and change its contract
so that it can be passed more items than fit on the root page. It's in a
better position than the callers to know how many items fit.

Move ginMergeItemPointers out of gindatapage.c, into a separate file.

These changes make no difference now, but reduce the footprint of Alexander
Korotkov's upcoming patch to pack item pointers more tightly.

1 files changed, 25 insertions, 24 deletions

diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index bda9c60279a..7b2c39965a7 100644
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -33,23 +33,26 @@ typedef struct
 
 
 /*
- * Cleans array of ItemPointer (removes dead pointers)
- * Results are always stored in *cleaned, which will be allocated
- * if it's needed. In case of *cleaned!=NULL caller is responsible to
- * have allocated enough space. *cleaned and items may point to the same
- * memory address.
+ * Vacuums a list of item pointers. The original size of the list is 'nitem',
+ * returns the number of items remaining afterwards.
+ *
+ * If *cleaned == NULL on entry, the original array is left unmodified; if
+ * any items are removed, a palloc'd copy of the result is stored in *cleaned.
+ * Otherwise *cleaned should point to the original array, in which case it's
+ * modified directly.
  */
-
-static uint32
-ginVacuumPostingList(GinVacuumState *gvs, ItemPointerData *items, uint32 nitem, ItemPointerData **cleaned)
+static int
+ginVacuumPostingList(GinVacuumState *gvs, ItemPointerData *items, int nitem,
+					 ItemPointerData **cleaned)
 {
-	uint32		i,
+	int			i,
 				j = 0;
 
+	Assert(*cleaned == NULL || *cleaned == items);
+
 	/*
 	 * just scan over ItemPointer array
 	 */
-
 	for (i = 0; i < nitem; i++)
 	{
 		if (gvs->callback(items + i, gvs->callback_state))
@@ -385,7 +388,8 @@ typedef struct DataPageDeleteStack
  * scans posting tree and deletes empty pages
  */
 static bool
-ginScanToDelete(GinVacuumState *gvs, BlockNumber blkno, bool isRoot, DataPageDeleteStack *parent, OffsetNumber myoff)
+ginScanToDelete(GinVacuumState *gvs, BlockNumber blkno, bool isRoot,
+				DataPageDeleteStack *parent, OffsetNumber myoff)
 {
 	DataPageDeleteStack *me;
 	Buffer		buffer;
@@ -431,15 +435,13 @@ ginScanToDelete(GinVacuumState *gvs, BlockNumber blkno, bool isRoot, DataPageDel
 
 	if (GinPageGetOpaque(page)->maxoff < FirstOffsetNumber)
 	{
+		/* the page is empty */
 		if (!(me->leftBlkno == InvalidBlockNumber && GinPageRightMost(page)))
 		{
 			/* we never delete right most branch */
 			Assert(!isRoot);
-			if (GinPageGetOpaque(page)->maxoff < FirstOffsetNumber)
-			{
-				ginDeletePage(gvs, blkno, me->leftBlkno, me->parent->blkno, myoff, me->parent->isRoot);
-				meDelete = TRUE;
-			}
+			ginDeletePage(gvs, blkno, me->leftBlkno, me->parent->blkno, myoff, me->parent->isRoot);
+			meDelete = TRUE;
 		}
 	}
 
@@ -517,11 +519,12 @@ ginVacuumEntryPage(GinVacuumState *gvs, Buffer buffer, BlockNumber *roots, uint3
 		else if (GinGetNPosting(itup) > 0)
 		{
 			/*
-			 * if we already create temporary page, we will make changes in
-			 * place
+			 * if we already created a temporary page, make changes in place
 			 */
 			ItemPointerData *cleaned = (tmppage == origpage) ? NULL : GinGetPosting(itup);
-			uint32		newN = ginVacuumPostingList(gvs, GinGetPosting(itup), GinGetNPosting(itup), &cleaned);
+			int			newN;
+
+			newN = ginVacuumPostingList(gvs, GinGetPosting(itup), GinGetNPosting(itup), &cleaned);
 
 			if (GinGetNPosting(itup) != newN)
 			{
@@ -530,15 +533,13 @@ ginVacuumEntryPage(GinVacuumState *gvs, Buffer buffer, BlockNumber *roots, uint3
 				GinNullCategory category;
 
 				/*
-				 * Some ItemPointers was deleted, so we should remake our
-				 * tuple
+				 * Some ItemPointers were deleted, recreate tuple.
 				 */
-
 				if (tmppage == origpage)
 				{
 					/*
-					 * On first difference we create temporary page in memory
-					 * and copies content in to it.
+					 * On first difference, create a temporary copy of the
+					 * page and copy the tuple's posting list to it.
 					 */
 					tmppage = PageGetTempPageCopy(origpage);