More GIN refactoring.

Split off the portion of ginInsertValue that inserts the tuple to current
level into a separate function, ginPlaceToPage. ginInsertValue's charter
is now to recurse up the tree to insert the downlink, when a page split is
required.

This is in preparation for a patch to change the way incomplete splits are
handled, which will need to do these operations separately. And IMHO makes
the code more readable anyway.

src/backend/access/gin/ginbtree.c

@@ -280,40 +280,19 @@ ginFindParents(GinBtree btree, GinBtreeStack *stack,
 }
 
 /*
- * Insert value (stored in GinBtree) to tree described by stack
+ * Returns true if the insertion is done, false if the page was split and
+ * downlink insertion is pending.
  *
- * During an index build, buildStats is non-null and the counters
- * it contains are incremented as needed.
- *
- * NB: the passed-in stack is freed, as though by freeGinBtreeStack.
+ * stack->buffer is locked on entry, and is kept locked.
  */
-void
-ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
+static bool
+ginPlaceToPage(GinBtree btree, BlockNumber rootBlkno, GinBtreeStack *stack,
+			   GinStatsData *buildStats)
 {
-	GinBtreeStack *parent;
-	BlockNumber rootBlkno;
-	Page		page,
-				rpage,
-				lpage;
-
-	/* extract root BlockNumber from stack */
-	Assert(stack != NULL);
-	parent = stack;
-	while (parent->parent)
-		parent = parent->parent;
-	rootBlkno = parent->blkno;
-	Assert(BlockNumberIsValid(rootBlkno));
-
-	/* this loop crawls up the stack until the insertion is complete */
-	for (;;)
-	{
+	Page		page = BufferGetPage(stack->buffer);
 	XLogRecData *rdata;
-		BlockNumber savedRightLink;
 	bool		fit;
 
-		page = BufferGetPage(stack->buffer);
-		savedRightLink = GinPageGetOpaque(page)->rightlink;
-
 	START_CRIT_SECTION();
 	fit = btree->placeToPage(btree, stack->buffer, stack->off, &rdata);
 	if (fit)
@@ -328,23 +307,26 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 			PageSetLSN(page, recptr);
 		}
 
-			LockBuffer(stack->buffer, GIN_UNLOCK);
 		END_CRIT_SECTION();
 
-			freeGinBtreeStack(stack);
-
-			return;
+		return true;
 	}
 	else
 	{
 		/* Didn't fit, have to split */
 		Buffer		rbuffer;
 		Page		newlpage;
+		BlockNumber savedRightLink;
+		GinBtreeStack *parent;
+		Page		lpage,
+					rpage;
 
 		END_CRIT_SECTION();
 
 		rbuffer = GinNewBuffer(btree->index);
 
+		savedRightLink = GinPageGetOpaque(page)->rightlink;
+
 		/*
 		 * newlpage is a pointer to memory page, it is not associated with
 		 * a buffer. stack->buffer is not touched yet.
@@ -375,7 +357,6 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 			((ginxlogSplit *) (rdata->data))->isRootSplit = TRUE;
 			((ginxlogSplit *) (rdata->data))->rrlink = InvalidBlockNumber;
 
-				page = BufferGetPage(stack->buffer);
 			lpage = BufferGetPage(lbuffer);
 			rpage = BufferGetPage(rbuffer);
 
@@ -405,11 +386,8 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 
 			UnlockReleaseBuffer(rbuffer);
 			UnlockReleaseBuffer(lbuffer);
-				LockBuffer(stack->buffer, GIN_UNLOCK);
 			END_CRIT_SECTION();
 
-				freeGinBtreeStack(stack);
-
 			/* During index build, count the newly-added root page */
 			if (buildStats)
 			{
@@ -419,7 +397,7 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 					buildStats->nEntryPages++;
 			}
 
-				return;
+			return true;
 		}
 		else
 		{
@@ -449,12 +427,54 @@ ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
 			}
 			UnlockReleaseBuffer(rbuffer);
 			END_CRIT_SECTION();
+
+			return false;
 		}
 	}
+}
 
-		btree->prepareDownlink(btree, stack->buffer);
+/*
+ * Insert value (stored in GinBtree) to tree described by stack
+ *
+ * During an index build, buildStats is non-null and the counters
+ * it contains are incremented as needed.
+ *
+ * NB: the passed-in stack is freed, as though by freeGinBtreeStack.
+ */
+void
+ginInsertValue(GinBtree btree, GinBtreeStack *stack, GinStatsData *buildStats)
+{
+	GinBtreeStack *parent;
+	BlockNumber rootBlkno;
+	Page		page;
+
+	/* extract root BlockNumber from stack */
+	Assert(stack != NULL);
+	parent = stack;
+	while (parent->parent)
+		parent = parent->parent;
+	rootBlkno = parent->blkno;
+	Assert(BlockNumberIsValid(rootBlkno));
+
+	/* this loop crawls up the stack until the insertion is complete */
+	for (;;)
+	{
+		bool done;
+
+		done = ginPlaceToPage(btree, rootBlkno, stack, buildStats);
+
+		/* just to be extra sure we don't delete anything by accident... */
 		btree->isDelete = FALSE;
 
+		if (done)
+		{
+			LockBuffer(stack->buffer, GIN_UNLOCK);
+			freeGinBtreeStack(stack);
+			break;
+		}
+
+		btree->prepareDownlink(btree, stack->buffer);
+
 		/* search parent to lock */
 		LockBuffer(parent->buffer, GIN_EXCLUSIVE);