Additional comments and an assert on the sqlite3BtreeInsert() overwrite

optimization.

FossilOrigin-Name: c1f0ae9d2981a19875103750379ad26f2575f878

manifest

@@ -1,5 +1,5 @@
-C In\ssqlite3BtreeInsert()\swhen\sreplacing\sa\sre-existing\srow,\stry\sto\soverwrite\nthe\scell\sdirectly\srather\sthan\sdeallocate\sand\sreallocate\sthe\scell.
-D 2016-12-09T17:32:51.304
+C Additional\scomments\sand\san\sassert\son\sthe\ssqlite3BtreeInsert()\soverwrite\noptimization.
+D 2016-12-09T18:09:42.258
 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 71f31086e48b0802990e95dbc30b65486f8c102d
+F src/btree.c 38bc160dfb270b4e005b23672310096c78eed4c8
 F src/btree.h 2349a588abcd7e0c04f984e15c5c777b61637583
 F src/btreeInt.h 10c4b77c2fb399580babbcc7cf652ac10dba796e
 F src/build.c 178f16698cbcb43402c343a9413fe22c99ffee21
@@ -1536,7 +1536,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 0ea3ece988883874bb88e3daaa220d7fc0cf36ef
-R 6946276392a9f20f9596069270e1a062
+P 0b86fbca6615ccf1f3a62614db577a8acbec6d9e
+R 11e5ca14997252e736d13429f6c59d06
 U drh
-Z ec93e08c56ba9575d48dea94960936a0
+Z db8419761e0f22ff22785868538d89ab

manifest.uuid

@@ -1 +1 @@
-0b86fbca6615ccf1f3a62614db577a8acbec6d9e
+c1f0ae9d2981a19875103750379ad26f2575f878

src/btree.c

@@ -8062,7 +8062,12 @@ int sqlite3BtreeInsert(
     }
     rc = clearCell(pPage, oldCell, &info);
     if( info.nSize==szNew && info.nLocal==info.nPayload ){
-      /* Overwrite the old cell with the new */
+      /* Overwrite the old cell with the new if they are the same size.
+      ** We could also try to do this if the old cell is smaller, then add
+      ** the leftover space to the free list.  But experiments show that
+      ** doing that is no faster then skipping this optimization and just
+      ** calling dropCell() and insertCell(). */
+      assert( rc==SQLITE_OK ); /* clearCell never fails when nLocal==nPayload */
       memcpy(oldCell, newCell, szNew);
       return SQLITE_OK;
     }