In balance_nonroot, try to combine dropCell/insertCell combinations for the

dividers into a cell overwrites.  This results in a very small (0.05%)
performance gain which is probably not worth the added complexity.

FossilOrigin-Name: 478627c9e949ffa97979cc91506b8c79a2aef484

manifest

@@ -1,5 +1,5 @@
-C When\sdoing\sthe\ssqlite3BtreeInsert()\soverwrite\soptimization,\smake\ssure\sthe\nmemcpy()\sdoes\snot\sextend\soff\sthe\send\sof\sthe\spage.
-D 2016-12-09T19:42:18.129
+C In\sbalance_nonroot,\stry\sto\scombine\sdropCell/insertCell\scombinations\sfor\sthe\ndividers\sinto\sa\scell\soverwrites.\s\sThis\sresults\sin\sa\svery\ssmall\s(0.05%)\nperformance\sgain\swhich\sis\sprobably\snot\sworth\sthe\sadded\scomplexity.
+D 2016-12-10T00:14:23.419
 F Makefile.in 7639c6a09da11a9c7c6f2630fc981ee588d1072d
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc b8ca53350ae545e3562403d5da2a69cec79308da
@@ -331,7 +331,7 @@ F src/auth.c 930b376a9c56998557367e6f7f8aaeac82a2a792
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c bc87dd3b062cc26edfe79918de2200ccb8d41e73
-F src/btree.c 217c9900de7cf04997aff25faabc366cfe84e8f1
+F src/btree.c 518b5a3692a3d2a4bee8628fa9a300d286377f7f
 F src/btree.h 2349a588abcd7e0c04f984e15c5c777b61637583
 F src/btreeInt.h 10c4b77c2fb399580babbcc7cf652ac10dba796e
 F src/build.c 178f16698cbcb43402c343a9413fe22c99ffee21
@@ -1536,7 +1536,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P c1f0ae9d2981a19875103750379ad26f2575f878
-R 956ba83a1c02ce8b54106bed68f282ac
+P 684ef4582ed19b2af22dda6fc085c70464f92f1b
+R d49f83677b094a47cc3a2fe599b3e886
+T *branch * failed-dropCell-opt
+T *sym-failed-dropCell-opt *
+T -sym-trunk *
 U drh
-Z 1db7deef38744b5038e919d70ebcde44
+Z fdade63ef998e2e74e6a87d6f3697018

manifest.uuid

@@ -1 +1 @@
-684ef4582ed19b2af22dda6fc085c70464f92f1b
+478627c9e949ffa97979cc91506b8c79a2aef484

src/btree.c

@@ -7017,12 +7017,18 @@ static int balance_nonroot(
   Pgno aPgno[NB+2];            /* Page numbers of new pages before shuffling */
   Pgno aPgOrder[NB+2];         /* Copy of aPgno[] used for sorting pages */
   u16 aPgFlags[NB+2];          /* flags field of new pages before shuffling */
-  CellArray b;                  /* Parsed information on cells being balanced */
+  CellArray b;                 /* Parsed information on cells being balanced */
+  struct DeferredDropCell {    /* Deferred calls to dropCell() for pParent */
+     u16 idx;                     /* The index of the cell to drop */
+     u16 sz;                      /* The size of the cell to drop */
+  } sDDC0, sDDC1;              /* Up to 2 deferred calls */
 
   memset(abDone, 0, sizeof(abDone));
   b.nCell = 0;
   b.apCell = 0;
   pBt = pParent->pBt;
+  sDDC0.sz = sDDC0.idx = 0;
+  sDDC1.sz = sDDC1.idx = 0;
   assert( sqlite3_mutex_held(pBt->mutex) );
   assert( sqlite3PagerIswriteable(pParent->pDbPage) );
 
@@ -7118,7 +7124,12 @@ static int balance_nonroot(
           apDiv[i] = &aOvflSpace[apDiv[i]-pParent->aData];
         }
       }
-      dropCell(pParent, i+nxDiv-pParent->nOverflow, szNew[i], &rc);
+      assert( sDDC1.sz==0 );
+      sDDC1 = sDDC0;
+      sDDC0.idx = i+nxDiv-pParent->nOverflow;
+      sDDC0.sz = szNew[i];
+//printf("dropCell:\n");
+//    dropCell(pParent, i+nxDiv-pParent->nOverflow, szNew[i], &rc);
     }
   }
 
@@ -7586,10 +7597,34 @@ static int balance_nonroot(
     iOvflSpace += sz;
     assert( sz<=pBt->maxLocal+23 );
     assert( iOvflSpace <= (int)pBt->pageSize );
-    insertCell(pParent, nxDiv+i, pCell, sz, pTemp, pNew->pgno, &rc);
+    if( sDDC0.idx==nxDiv+i && sDDC0.sz==sz ){
+      /* overwrite */
+      unsigned char *oldCell = findCell(pParent, sDDC0.idx);
+//printf("overwrite: pg=%d idx=%d sz=%d\n", pParent->pgno, sDDC0.idx, sDDC0.sz);
+      memcpy(oldCell+4, pCell+4, sz-4);
+      put4byte(oldCell, pNew->pgno);
+      sDDC0 = sDDC1;
+      sDDC1.sz = 0;
+    }else{
+      if( sDDC0.sz>0 ){
+        if( sDDC1.sz>0 ){
+//printf("dropCell: pg=%d idx=%d sz=%d\n", pParent->pgno, sDDC1.idx, sDDC1.sz);
+          dropCell(pParent, sDDC1.idx, sDDC1.sz, &rc);
+          sDDC1.sz = 0;
+        }
+//printf("dropCell: pg=%d idx=%d sz=%d\n", pParent->pgno, sDDC0.idx, sDDC0.sz);
+        dropCell(pParent, sDDC0.idx, sDDC0.sz, &rc);
+        sDDC0.sz = 0;
+        if( rc ) goto balance_cleanup;
+      }
+//printf("insertCell: pg=%d idx=%d sz=%d\n", pParent->pgno, nxDiv+i, sz);
+      insertCell(pParent, nxDiv+i, pCell, sz, pTemp, pNew->pgno, &rc);
+    }
     if( rc!=SQLITE_OK ) goto balance_cleanup;
     assert( sqlite3PagerIswriteable(pParent->pDbPage) );
   }
+  if( sDDC1.sz ) dropCell(pParent, sDDC1.idx, sDDC1.sz, &rc);
+  if( sDDC0.sz ) dropCell(pParent, sDDC0.idx, sDDC0.sz, &rc);
 
   /* Now update the actual sibling pages. The order in which they are updated
   ** is important, as this code needs to avoid disrupting any page from which