Index: ext/fts2/fts2.c
==================================================================
--- ext/fts2/fts2.c
+++ ext/fts2/fts2.c
@@ -157,13 +157,15 @@
 ** Otherwise, for terms greater than or equal to pTerm[i] but less
 ** than pTerm[i+1], the subtree for that term will be rooted at
 ** iBlockid+i.
 **
 ** New data is spilled to a new interior node at the same height when
-** the current node exceeds INTERIOR_MAX bytes (default 2048).  The
-** interior nodes at a given height are naturally tracked by interior
-** nodes at height+1, and so on.
+** the current node exceeds INTERIOR_MAX bytes (default 2048).
+** INTERIOR_MIN_TERMS (default 7) keeps large terms from monopolizing
+** interior nodes and making the tree too skinny.  The interior nodes
+** at a given height are naturally tracked by interior nodes at
+** height+1, and so on.
 **
 **
 **** Segment directory ****
 ** The segment directory in table %_segdir stores meta-information for
 ** merging and deleting segments, and also the root node of the
@@ -3595,10 +3597,20 @@
 ** format.
 */
 
 /* How large interior nodes can grow. */
 #define INTERIOR_MAX 2048
+
+/* Minimum number of terms per interior node (except the root). This
+** prevents large terms from making the tree too skinny - must be >0
+** so that the tree always makes progress.  Note that the min tree
+** fanout will be INTERIOR_MIN_TERMS+1.
+*/
+#define INTERIOR_MIN_TERMS 7
+#if INTERIOR_MIN_TERMS<1
+# error INTERIOR_MIN_TERMS must be greater than 0.
+#endif
 
 /* ROOT_MAX controls how much data is stored inline in the segment
 ** directory.
 */
 /* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
@@ -3640,10 +3652,11 @@
 typedef struct InteriorWriter {
   int iHeight;                   /* from 0 at leaves. */
   InteriorBlock *first, *last;
   struct InteriorWriter *parentWriter;
 
+  sqlite_int64 iOpeningChildBlock; /* First child block in block "last". */
 #ifndef NDEBUG
   sqlite_int64 iLastChildBlock;  /* for consistency checks. */
 #endif
 } InteriorWriter;
 
@@ -3657,10 +3670,11 @@
   InteriorBlock *block;
   assert( iHeight>0 );
   CLEAR(pWriter);
 
   pWriter->iHeight = iHeight;
+  pWriter->iOpeningChildBlock = iChildBlock;
 #ifndef NDEBUG
   pWriter->iLastChildBlock = iChildBlock;
 #endif
   block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
   pWriter->last = pWriter->first = block;
@@ -3678,15 +3692,19 @@
 #ifndef NDEBUG
   pWriter->iLastChildBlock++;
 #endif
   assert( pWriter->iLastChildBlock==iChildBlock );
 
-  if( pWriter->last->data.nData+n+nTerm>INTERIOR_MAX ){
-    /* Overflow to a new block. */
+  /* Overflow to a new block if the new term makes the current block
+  ** too big, and the current block already has enough terms.
+  */
+  if( pWriter->last->data.nData+n+nTerm>INTERIOR_MAX &&
+      iChildBlock-pWriter->iOpeningChildBlock>INTERIOR_MIN_TERMS ){
     pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
                                            pTerm, nTerm);
     pWriter->last = pWriter->last->next;
+    pWriter->iOpeningChildBlock = iChildBlock;
   }else{
     dataBufferAppend2(&pWriter->last->data, c, n, pTerm, nTerm);
   }
 }