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, 11 insertions, 3 deletions

diff --git a/src/backend/access/gin/ginentrypage.c b/src/backend/access/gin/ginentrypage.c
index 7733028fba8..0ed0a3db7eb 100644
--- a/src/backend/access/gin/ginentrypage.c
+++ b/src/backend/access/gin/ginentrypage.c
@@ -486,9 +486,12 @@ entryPreparePage(GinBtree btree, Page page, OffsetNumber off)
 
 /*
  * Place tuple on page and fills WAL record
+ *
+ * If the tuple doesn't fit, returns false without modifying the page.
  */
-static void
-entryPlaceToPage(GinBtree btree, Buffer buf, OffsetNumber off, XLogRecData **prdata)
+static bool
+entryPlaceToPage(GinBtree btree, Buffer buf, OffsetNumber off,
+				 XLogRecData **prdata)
 {
 	Page		page = BufferGetPage(buf);
 	OffsetNumber placed;
@@ -498,6 +501,10 @@ entryPlaceToPage(GinBtree btree, Buffer buf, OffsetNumber off, XLogRecData **prd
 	static XLogRecData rdata[3];
 	static ginxlogInsert data;
 
+	/* quick exit if it doesn't fit */
+	if (!entryIsEnoughSpace(btree, buf, off))
+		return false;
+
 	*prdata = rdata;
 	data.updateBlkno = entryPreparePage(btree, page, off);
 
@@ -543,6 +550,8 @@ entryPlaceToPage(GinBtree btree, Buffer buf, OffsetNumber off, XLogRecData **prd
 	rdata[cnt].next = NULL;
 
 	btree->entry = NULL;
+
+	return true;
 }
 
 /*
@@ -724,7 +733,6 @@ ginPrepareEntryScan(GinBtree btree, OffsetNumber attnum,
 	btree->findItem = entryLocateLeafEntry;
 	btree->findChildPtr = entryFindChildPtr;
 	btree->getLeftMostPage = entryGetLeftMostPage;
-	btree->isEnoughSpace = entryIsEnoughSpace;
 	btree->placeToPage = entryPlaceToPage;
 	btree->splitPage = entrySplitPage;
 	btree->fillRoot = ginEntryFillRoot;