diff --git a/VERSION b/VERSION
index 30291cba22..afad818663 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-3.10.0
+3.11.0
diff --git a/configure b/configure
index 174f41ae24..850d986306 100755
--- a/configure
+++ b/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.69 for sqlite 3.10.0.
+# Generated by GNU Autoconf 2.69 for sqlite 3.11.0.
 #
 #
 # Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
@@ -726,8 +726,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='sqlite'
 PACKAGE_TARNAME='sqlite'
-PACKAGE_VERSION='3.10.0'
-PACKAGE_STRING='sqlite 3.10.0'
+PACKAGE_VERSION='3.11.0'
+PACKAGE_STRING='sqlite 3.11.0'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -1460,7 +1460,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures sqlite 3.10.0 to adapt to many kinds of systems.
+\`configure' configures sqlite 3.11.0 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1525,7 +1525,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of sqlite 3.10.0:";;
+     short | recursive ) echo "Configuration of sqlite 3.11.0:";;
    esac
   cat <<\_ACEOF
 
@@ -1646,7 +1646,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-sqlite configure 3.10.0
+sqlite configure 3.11.0
 generated by GNU Autoconf 2.69
 
 Copyright (C) 2012 Free Software Foundation, Inc.
@@ -2065,7 +2065,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by sqlite $as_me 3.10.0, which was
+It was created by sqlite $as_me 3.11.0, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   $ $0 $@
@@ -12023,7 +12023,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by sqlite $as_me 3.10.0, which was
+This file was extended by sqlite $as_me 3.11.0, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -12089,7 +12089,7 @@ _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config="`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`"
 ac_cs_version="\\
-sqlite config.status 3.10.0
+sqlite config.status 3.11.0
 configured by $0, generated by GNU Autoconf 2.69,
   with options \\"\$ac_cs_config\\"
 
diff --git a/manifest b/manifest
index 6158acb724..5a749962b4 100644
--- a/manifest
+++ b/manifest
@@ -1,10 +1,10 @@
-C Add\sthe\sfts5speed.tcl\sscript\sto\sext/fts5/tool/.
-D 2016-01-11T18:23:07.397
+C Merge\strunk\swith\sthis\sbranch.
+D 2016-01-11T18:30:34.152
 F Makefile.in 7c8cc4c2f0179efc6fa9492141d1fb65f4807054
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc e45d8b9b56dfa3f2cd860b2c28bd9d304513b042
 F README.md 8ecc12493ff9f820cdea6520a9016001cb2e59b7
-F VERSION 8b9d3ac6f1962f94e06ba05462422a544f9c4e36
+F VERSION 866588d1edf0ccb5b0d33896974338f97564f719
 F aclocal.m4 a5c22d164aff7ed549d53a90fa56d56955281f50
 F art/sqlite370.eps aa97a671332b432a54e1d74ff5e8775be34200c2
 F art/sqlite370.ico af56c1d00fee7cd4753e8631ed60703ed0fc6e90
@@ -29,7 +29,7 @@ F autoconf/tea/win/rules.vc c511f222b80064096b705dbeb97060ee1d6b6d63
 F config.guess 226d9a188c6196f3033ffc651cbc9dcee1a42977
 F config.h.in 42b71ad3fe21c9e88fa59e8458ca1a6bc72eb0c0
 F config.sub 9ebe4c3b3dab6431ece34f16828b594fb420da55
-F configure e511ceefe595e35051933a90c848ab4fa1d48add x
+F configure b4519bb54fff37e7cde9d03d8f2946f18d5d0086 x
 F configure.ac fcfc67b323d32daaa3e46cf7782d9465ed423a6d
 F contrib/sqlitecon.tcl 210a913ad63f9f991070821e599d600bd913e0ad
 F doc/lemon.html 334dbf6621b8fb8790297ec1abf3cfa4621709d1
@@ -280,21 +280,21 @@ F src/attach.c e944d0052b577703b9b83aac1638452ff42a8395
 F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
 F src/backup.c 2869a76c03eb393ee795416e2387005553df72bc
 F src/bitvec.c 1a78d450a17c5016710eec900bedfc5729bf9bdf
-F src/btmutex.c 45a968cc85afed9b5e6cf55bf1f42f8d18107f79
-F src/btree.c 4d3452b2a3daf875490ac4f0a278da7f85fabe12
-F src/btree.h 2d76dee44704c47eed323356a758662724b674a0
+F src/btmutex.c bc87dd3b062cc26edfe79918de2200ccb8d41e73
+F src/btree.c 6bd9b3d778a023e2238a81cd0b87b00085220e0e
+F src/btree.h 68ef301795e00cdf1d3ab93abc44a43b7fe771e0
 F src/btreeInt.h b5f2651b41808f038dee9282c5dc0232ce6532d3
-F src/build.c d8006e9030c61b9495d0b2f724edd3fcdae16930
+F src/build.c 9d497ff4bf3c82cecb520436e0e9963785627583
 F src/callback.c 7b44ce59674338ad48b0e84e7b72f935ea4f68b0
 F src/complete.c addcd8160b081131005d5bc2d34adf20c1c5c92f
 F src/ctime.c 60e135af364d777a9ab41c97e5e89cd224da6198
 F src/date.c e4655393bb403fa310eef66cc4583d75d4d7fd93
 F src/dbstat.c ffd63fc8ba7541476ced189b95e95d7f2bc63f78
 F src/delete.c 00af9f08a15ddc5cba5962d3d3e5bf2d67b2e7da
-F src/expr.c 38790e65d1219f2b7dc26458f39a5252fe7c60cd
+F src/expr.c fe55c489362d1429c364e98c877514f4455f45a6
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c e18b3dff7d47c7bcac5ac4fc178a89b9fd322b44
-F src/func.c cf5e10af9125b245f1b962e8ba4d520a37818795
+F src/func.c ccaf46fa98f795673afbfab73dff7c18db88f3cd
 F src/global.c bd5a0af3f30b0c01be6db756c626cd3c33a3d260
 F src/hash.c 4263fbc955f26c2e8cdc0cf214bc42435aa4e4f5
 F src/hash.h c8f3c31722cf3277d03713909761e152a5b81094
@@ -309,7 +309,7 @@ F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c 6919bcf12f221868ea066eec27e579fed95ce98b
 F src/mem2.c f1940d9e91948dd6a908fbb9ce3835c36b5d83c3
 F src/mem3.c 8768ac94694f31ffaf8b4d0ea5dc08af7010a35a
-F src/mem5.c 262055c242fa7db59c5f07ad77fdc4e97888c054
+F src/mem5.c 71f81a11fc5e29a57428761ab38a7bf2ef4ee19d
 F src/memjournal.c 3eb2c0b51adbd869cb6a44780323f05fa904dc85
 F src/msvc.h d9ba56c6851227ab44b3f228a35f3f5772296495
 F src/mutex.c 8e45800ee78e0cd1f1f3fe8e398853307f4a085c
@@ -322,14 +322,14 @@ F src/os.c 8fd25588eeba74068d41102d26810e216999b6c8
 F src/os.h 3e57a24e2794a94d3cf2342c6d9a884888cd96bf
 F src/os_common.h abdb9a191a367793268fe553d25bab894e986a0e
 F src/os_setup.h c9d4553b5aaa6f73391448b265b89bed0b890faa
-F src/os_unix.c 0ca6d8710366fbb01a275160f018334cd347cbda
+F src/os_unix.c 82986e1e75782b54da7822dca42d36d974fc2948
 F src/os_win.c 386fba30419e8458b13209781c2af5590eab2811
 F src/os_win.h eb7a47aa17b26b77eb97e4823f20a00b8bda12ca
 F src/pager.c 58d2593612acb6b542de6715b4af397ea1fa0a35
 F src/pager.h bf25005b4656cd805af43487c3139fca9678d0cc
-F src/parse.y 23737e649c26ce327603799e57f5c2ff50e5e6ba
+F src/parse.y caad1e98edeca6960493d0c60d31b76820dd7776
 F src/pcache.c 73895411fa6b7bd6f0091212feabbe833b358d23
-F src/pcache.h 1ff11adce609ba7de139b6abfabaf9a2bac947b5
+F src/pcache.h 4d0ccaad264d360981ec5e6a2b596d6e85242545
 F src/pcache1.c 72f644dc9e1468c72922eff5904048427b817051
 F src/pragma.c f3e7147299ca05ef4304a36f1fd6e002729c72c6
 F src/pragma.h 64c78a648751b9f4f297276c4eb7507b14b4628c
@@ -338,16 +338,16 @@ F src/printf.c af589a27b7d40f6f4f704e9eea99f02f18ad6d32
 F src/random.c ba2679f80ec82c4190062d756f22d0c358180696
 F src/resolve.c a83b41104e6ff69855d03cd0aaa09e93927ec39f
 F src/rowset.c eccf6af6d620aaa4579bd3b72c1b6395d9e9fa1e
-F src/select.c f8fded11fc443a9f5a73cc5db069d06b34460e2f
+F src/select.c d84c091185bc160c349e8bf460ebd084dbd77e64
 F src/shell.c ed71dc7679e6f087a3f1ea3f9dae4b0fae7209c3
 F src/sqlite.h.in 7d87d71b9a4689c51fa092f48f16590ff71558e3
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h dfbe62ffd95b99afe2140d8c35b180d11924072d
-F src/sqliteInt.h f97614d43833bae0ed6c51ac8e550f0099a1d0ba
+F src/sqliteInt.h b8ccd34a919e4b6bab8c4164046330002aa9a27a
 F src/sqliteLimit.h 216557999cb45f2e3578ed53ebefe228d779cb46
 F src/status.c 70912d7be68e9e2dbc4010c93d344af61d4c59ba
 F src/table.c 51b46b2a62d1b3a959633d593b89bab5e2c9155e
-F src/tclsqlite.c d9439b6a910985b7fff43ba6756bcef00de22649
+F src/tclsqlite.c 82979239a896992f9b78efec81cfda05d316a7d0
 F src/test1.c 4f1b42699068b7806af3111786f5ad760c2c1ff7
 F src/test2.c 5586f43fcd9a1be0830793cf9d354082c261b25b
 F src/test3.c a8887dabbbee3059af338f20d290084a63ed1b0f
@@ -403,20 +403,20 @@ F src/update.c 17332f9fe818cbc0444c36a811800af8498af4c3
 F src/utf.c 32d7f82aa921322f3e1c956f4b58f019ebd2c6b3
 F src/util.c e802e8e311a0d6c48cd1b3e89db164f6f0248d70
 F src/vacuum.c 2ddd5cad2a7b9cef7f9e431b8c7771634c6b1701
-F src/vdbe.c 6ac8e5d808d48afc369316e147c191102f0584c1
+F src/vdbe.c 6572d00eefeaa0b14b325fdf3a409920ec3fee82
 F src/vdbe.h efb7a8c1459e31f3ea4377824c6a7e4cb5068637
-F src/vdbeInt.h 75c2e82ee3357e9210c06474f8d9bdf12c81105d
+F src/vdbeInt.h 42eefa4f9e7432b9968d321b44e48821ec13b189
 F src/vdbeapi.c 020681b943e77766b32ae1cddf86d7831b7374ca
-F src/vdbeaux.c 3308a07a6b0b64e22e83cbcc76773eaf330b056a
+F src/vdbeaux.c 5d8c7c04e0f677033efb1292248a5f9056bbc34c
 F src/vdbeblob.c fdc4a81605ae7a35ae94a55bd768b66d6be16f15
 F src/vdbemem.c fdd1578e47bea61390d472de53c565781d81e045
 F src/vdbesort.c a7ec02da4494c59dfd071126dd3726be5a11459d
 F src/vdbetrace.c 8befe829faff6d9e6f6e4dee5a7d3f85cc85f1a0
 F src/vtab.c 2a8b44aa372c33f6154208e7a7f6c44254549806
 F src/vxworks.h c18586c8edc1bddbc15c004fa16aeb1e1342b4fb
-F src/wal.c 974928c988681c5157202c79dd9f26afaa7b5086
+F src/wal.c 92ca9e7923c337c497e4c9aa7edac800e269a1d8
 F src/wal.h 907943dfdef10b583e81906679a347e0ec6f1b1b
-F src/walker.c 2e14d17f592d176b6dc879c33fbdec4fbccaa2ba
+F src/walker.c 0f142b5bd3ed2041fc52d773880748b212e63354
 F src/where.c c6d3d2f6af57d574a7365ee2b225a5024f2a6bec
 F src/whereInt.h 78b6b4de94db84aecbdc07fe3e38f648eb391e9a
 F src/wherecode.c dfbfe198e418b01f208b489e088edd230c91a4e7
@@ -1066,7 +1066,7 @@ F test/tclsqlite.test 7fb866443c7deceed22b63948ccd6f76b52ad054
 F test/tempdb.test 19d0f66e2e3eeffd68661a11c83ba5e6ace9128c
 F test/temptable.test d2c9b87a54147161bcd1822e30c1d1cd891e5b30
 F test/temptrigger.test 8ec228b0db5d7ebc4ee9b458fc28cb9e7873f5e1
-F test/tester.tcl 9df86ab273a0877ffb4ec26c255166dcdca4c278
+F test/tester.tcl af4749cf4abf04291710c5e73f40bc8f411bae86
 F test/thread001.test 9f22fd3525a307ff42a326b6bc7b0465be1745a5
 F test/thread002.test e630504f8a06c00bf8bbe68528774dd96aeb2e58
 F test/thread003.test ee4c9efc3b86a6a2767516a37bd64251272560a7
@@ -1279,12 +1279,12 @@ F test/vtabC.test 4528f459a13136f982e75614d120aef165f17292
 F test/vtabD.test 05b3f1d77117271671089e48719524b676842e96
 F test/vtabE.test d5024aa42754962f6bb0afd261681686488e7afe
 F test/vtabF.test fd5ad376f5a34fe0891df1f3cddb4fe7c3eb077e
-F test/vtabH.test 492ba03dcb7bb8fedcc53f258c410d04013adbc9
+F test/vtabH.test 5f5157a1501d9889ec35c1a1832f69612dd31444
 F test/vtabI.test 751b07636700dbdea328e4265b6077ccd6811a3f
 F test/vtab_alter.test 9e374885248f69e251bdaacf480b04a197f125e5
 F test/vtab_err.test 0d4d8eb4def1d053ac7c5050df3024fd47a3fbd8
 F test/vtab_shared.test ea8778d5b0df200adef2ca7c00c3c37d4375f772
-F test/wal.test dbfc482e10c7263298833bb1fc60b3ac9d6340a1
+F test/wal.test 65bfc68f3f09dcbc62cee9f794e560428d96cec7
 F test/wal2.test 1f841d2048080d32f552942e333fd99ce541dada
 F test/wal3.test b1d425f68a1f61d12563f0fa1ee6fca7d5afabf4
 F test/wal4.test 4744e155cd6299c6bd99d3eab1c82f77db9cdb3c
@@ -1306,6 +1306,7 @@ F test/walfault.test 1f8389f7709877e9b4cc679033d71d6fe529056b
 F test/walhook.test ed00a40ba7255da22d6b66433ab61fab16a63483
 F test/walmode.test 4022fe03ae6e830583672caa101f046438a0473c
 F test/walnoshm.test 84ca10c544632a756467336b7c3b864d493ee496
+F test/waloverwrite.test 8702964967c2f28204f0b4f27af65da81999fc99
 F test/walpersist.test 8c6b7e3ec1ba91b5e4dc4e0921d6d3f87cd356a6
 F test/walro.test 34422d1d95aaff0388f0791ec20edb34e2a3ed57
 F test/walshared.test 0befc811dcf0b287efae21612304d15576e35417
@@ -1411,7 +1412,7 @@ F tool/vdbe_profile.tcl 246d0da094856d72d2c12efec03250d71639d19f
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 0e3c545423246231ddac8fed2f103d71d556e17f
-R af2ae430a57fbc5161db0dbbd31b8a3f
+P 2c0b93553ebb00a70c611eb8dac021877933f088 ecc98bef43c2fd07d64e4efddf340929a875ebac
+R fac95fe8d4249da246cad11b14ac9297
 U dan
-Z 7e47e5a1c7084b8fa203746692b6702a
+Z 0acdab0d7c32bec7117a883df7ebebf7
diff --git a/manifest.uuid b/manifest.uuid
index 7a083e6ea4..0ab6f5ff10 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-2c0b93553ebb00a70c611eb8dac021877933f088
\ No newline at end of file
+a73d245f2e523a57163bc93d9fb6a74c4cdf21e7
\ No newline at end of file
diff --git a/src/btmutex.c b/src/btmutex.c
index c9c8572dfb..c1ebff9604 100644
--- a/src/btmutex.c
+++ b/src/btmutex.c
@@ -169,21 +169,6 @@ int sqlite3BtreeHoldsMutex(Btree *p){
 #endif
 
 
-#ifndef SQLITE_OMIT_INCRBLOB
-/*
-** Enter and leave a mutex on a Btree given a cursor owned by that
-** Btree.  These entry points are used by incremental I/O and can be
-** omitted if that module is not used.
-*/
-void sqlite3BtreeEnterCursor(BtCursor *pCur){
-  sqlite3BtreeEnter(pCur->pBtree);
-}
-void sqlite3BtreeLeaveCursor(BtCursor *pCur){
-  sqlite3BtreeLeave(pCur->pBtree);
-}
-#endif /* SQLITE_OMIT_INCRBLOB */
-
-
 /*
 ** Enter the mutex on every Btree associated with a database
 ** connection.  This is needed (for example) prior to parsing
@@ -217,14 +202,6 @@ void sqlite3BtreeLeaveAll(sqlite3 *db){
   }
 }
 
-/*
-** Return true if a particular Btree requires a lock.  Return FALSE if
-** no lock is ever required since it is not sharable.
-*/
-int sqlite3BtreeSharable(Btree *p){
-  return p->sharable;
-}
-
 #ifndef NDEBUG
 /*
 ** Return true if the current thread holds the database connection
@@ -298,4 +275,23 @@ void sqlite3BtreeEnterAll(sqlite3 *db){
   }
 }
 #endif /* if SQLITE_THREADSAFE */
+
+#ifndef SQLITE_OMIT_INCRBLOB
+/*
+** Enter a mutex on a Btree given a cursor owned by that Btree. 
+**
+** These entry points are used by incremental I/O only. Enter() is required 
+** any time OMIT_SHARED_CACHE is not defined, regardless of whether or not 
+** the build is threadsafe. Leave() is only required by threadsafe builds.
+*/
+void sqlite3BtreeEnterCursor(BtCursor *pCur){
+  sqlite3BtreeEnter(pCur->pBtree);
+}
+# if SQLITE_THREADSAFE
+void sqlite3BtreeLeaveCursor(BtCursor *pCur){
+  sqlite3BtreeLeave(pCur->pBtree);
+}
+# endif
+#endif /* ifndef SQLITE_OMIT_INCRBLOB */
+
 #endif /* ifndef SQLITE_OMIT_SHARED_CACHE */
diff --git a/src/btree.c b/src/btree.c
index f5feff8a4c..77552d5831 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -450,6 +450,10 @@ static void releasePage(MemPage *pPage);  /* Forward reference */
 static int cursorHoldsMutex(BtCursor *p){
   return sqlite3_mutex_held(p->pBt->mutex);
 }
+static int cursorOwnsBtShared(BtCursor *p){
+  assert( cursorHoldsMutex(p) );
+  return (p->pBtree->db==p->pBt->db);
+}
 #endif
 
 /*
@@ -786,7 +790,7 @@ static int btreeMoveto(
 static int btreeRestoreCursorPosition(BtCursor *pCur){
   int rc;
   int skipNext;
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState>=CURSOR_REQUIRESEEK );
   if( pCur->eState==CURSOR_FAULT ){
     return pCur->skipNext;
@@ -3126,7 +3130,6 @@ int sqlite3BtreeNewDb(Btree *p){
 ** proceed.
 */
 int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
-  sqlite3 *pBlock = 0;
   BtShared *pBt = p->pBt;
   int rc = SQLITE_OK;
 
@@ -3149,27 +3152,30 @@ int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
   }
 
 #ifndef SQLITE_OMIT_SHARED_CACHE
-  /* If another database handle has already opened a write transaction 
-  ** on this shared-btree structure and a second write transaction is
-  ** requested, return SQLITE_LOCKED.
-  */
-  if( (wrflag && pBt->inTransaction==TRANS_WRITE)
-   || (pBt->btsFlags & BTS_PENDING)!=0
-  ){
-    pBlock = pBt->pWriter->db;
-  }else if( wrflag>1 ){
-    BtLock *pIter;
-    for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
-      if( pIter->pBtree!=p ){
-        pBlock = pIter->pBtree->db;
-        break;
+  {
+    sqlite3 *pBlock = 0;
+    /* If another database handle has already opened a write transaction 
+    ** on this shared-btree structure and a second write transaction is
+    ** requested, return SQLITE_LOCKED.
+    */
+    if( (wrflag && pBt->inTransaction==TRANS_WRITE)
+     || (pBt->btsFlags & BTS_PENDING)!=0
+    ){
+      pBlock = pBt->pWriter->db;
+    }else if( wrflag>1 ){
+      BtLock *pIter;
+      for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
+        if( pIter->pBtree!=p ){
+          pBlock = pIter->pBtree->db;
+          break;
+        }
       }
     }
-  }
-  if( pBlock ){
-    sqlite3ConnectionBlocked(p->db, pBlock);
-    rc = SQLITE_LOCKED_SHAREDCACHE;
-    goto trans_begun;
+    if( pBlock ){
+      sqlite3ConnectionBlocked(p->db, pBlock);
+      rc = SQLITE_LOCKED_SHAREDCACHE;
+      goto trans_begun;
+    }
   }
 #endif
 
@@ -4286,7 +4292,7 @@ int sqlite3BtreeKeySize(BtCursor *pCur, i64 *pSize){
 ** to return an integer result code for historical reasons.
 */
 int sqlite3BtreeDataSize(BtCursor *pCur, u32 *pSize){
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   assert( pCur->iPage>=0 );
   assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
@@ -4666,7 +4672,7 @@ int sqlite3BtreeData(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
   }
 #endif
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   rc = restoreCursorPosition(pCur);
   if( rc==SQLITE_OK ){
     assert( pCur->eState==CURSOR_VALID );
@@ -4704,7 +4710,7 @@ static const void *fetchPayload(
   assert( pCur!=0 && pCur->iPage>=0 && pCur->apPage[pCur->iPage]);
   assert( pCur->eState==CURSOR_VALID );
   assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
   assert( pCur->info.nSize>0 );
   assert( pCur->info.pPayload>pCur->apPage[pCur->iPage]->aData || CORRUPT_DB );
@@ -4750,7 +4756,7 @@ const void *sqlite3BtreeDataFetch(BtCursor *pCur, u32 *pAmt){
 static int moveToChild(BtCursor *pCur, u32 newPgno){
   BtShared *pBt = pCur->pBt;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
   assert( pCur->iPage>=0 );
@@ -4796,7 +4802,7 @@ static void assertParentIndex(MemPage *pParent, int iIdx, Pgno iChild){
 ** the largest cell index.
 */
 static void moveToParent(BtCursor *pCur){
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   assert( pCur->iPage>0 );
   assert( pCur->apPage[pCur->iPage] );
@@ -4836,7 +4842,7 @@ static int moveToRoot(BtCursor *pCur){
   MemPage *pRoot;
   int rc = SQLITE_OK;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
   assert( CURSOR_VALID   < CURSOR_REQUIRESEEK );
   assert( CURSOR_FAULT   > CURSOR_REQUIRESEEK );
@@ -4915,7 +4921,7 @@ static int moveToLeftmost(BtCursor *pCur){
   int rc = SQLITE_OK;
   MemPage *pPage;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   while( rc==SQLITE_OK && !(pPage = pCur->apPage[pCur->iPage])->leaf ){
     assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
@@ -4940,7 +4946,7 @@ static int moveToRightmost(BtCursor *pCur){
   int rc = SQLITE_OK;
   MemPage *pPage = 0;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   while( !(pPage = pCur->apPage[pCur->iPage])->leaf ){
     pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
@@ -4961,7 +4967,7 @@ static int moveToRightmost(BtCursor *pCur){
 int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
   int rc;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
   rc = moveToRoot(pCur);
   if( rc==SQLITE_OK ){
@@ -4984,7 +4990,7 @@ int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
 int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
   int rc;
  
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
 
   /* If the cursor already points to the last entry, this is a no-op. */
@@ -5062,7 +5068,7 @@ int sqlite3BtreeMovetoUnpacked(
   int rc;
   RecordCompare xRecordCompare;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
   assert( pRes );
   assert( (pIdxKey==0)==(pCur->pKeyInfo==0) );
@@ -5310,7 +5316,7 @@ static SQLITE_NOINLINE int btreeNext(BtCursor *pCur, int *pRes){
   int idx;
   MemPage *pPage;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
   assert( *pRes==0 );
   if( pCur->eState!=CURSOR_VALID ){
@@ -5374,7 +5380,7 @@ static SQLITE_NOINLINE int btreeNext(BtCursor *pCur, int *pRes){
 }
 int sqlite3BtreeNext(BtCursor *pCur, int *pRes){
   MemPage *pPage;
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pRes!=0 );
   assert( *pRes==0 || *pRes==1 );
   assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
@@ -5419,7 +5425,7 @@ static SQLITE_NOINLINE int btreePrevious(BtCursor *pCur, int *pRes){
   int rc;
   MemPage *pPage;
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pRes!=0 );
   assert( *pRes==0 );
   assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
@@ -5475,7 +5481,7 @@ static SQLITE_NOINLINE int btreePrevious(BtCursor *pCur, int *pRes){
   return rc;
 }
 int sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pRes!=0 );
   assert( *pRes==0 || *pRes==1 );
   assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
@@ -7955,7 +7961,7 @@ int sqlite3BtreeInsert(
     return pCur->skipNext;
   }
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( (pCur->curFlags & BTCF_WriteFlag)!=0
               && pBt->inTransaction==TRANS_WRITE
               && (pBt->btsFlags & BTS_READ_ONLY)==0 );
@@ -8102,7 +8108,7 @@ int sqlite3BtreeDelete(BtCursor *pCur, int bPreserve){
   u16 szCell;                          /* Size of the cell being deleted */
   int bSkipnext = 0;                   /* Leaf cursor in SKIPNEXT state */
 
-  assert( cursorHoldsMutex(pCur) );
+  assert( cursorOwnsBtShared(pCur) );
   assert( pBt->inTransaction==TRANS_WRITE );
   assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
   assert( pCur->curFlags & BTCF_WriteFlag );
@@ -9564,7 +9570,7 @@ int sqlite3BtreeLockTable(Btree *p, int iTab, u8 isWriteLock){
 */
 int sqlite3BtreePutData(BtCursor *pCsr, u32 offset, u32 amt, void *z){
   int rc;
-  assert( cursorHoldsMutex(pCsr) );
+  assert( cursorOwnsBtShared(pCsr) );
   assert( sqlite3_mutex_held(pCsr->pBtree->db->mutex) );
   assert( pCsr->curFlags & BTCF_Incrblob );
 
@@ -9671,3 +9677,12 @@ int sqlite3BtreeIsReadonly(Btree *p){
 ** Return the size of the header added to each page by this module.
 */
 int sqlite3HeaderSizeBtree(void){ return ROUND8(sizeof(MemPage)); }
+
+#if !defined(SQLITE_OMIT_SHARED_CACHE)
+/*
+** Return true if the Btree passed as the only argument is sharable.
+*/
+int sqlite3BtreeSharable(Btree *p){
+  return p->sharable;
+}
+#endif
diff --git a/src/btree.h b/src/btree.h
index 09b713f3db..2f398e7bba 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -287,15 +287,17 @@ void sqlite3BtreeCursorList(Btree*);
 #ifndef SQLITE_OMIT_SHARED_CACHE
   void sqlite3BtreeEnter(Btree*);
   void sqlite3BtreeEnterAll(sqlite3*);
+  int sqlite3BtreeSharable(Btree*);
+  void sqlite3BtreeEnterCursor(BtCursor*);
 #else
 # define sqlite3BtreeEnter(X) 
 # define sqlite3BtreeEnterAll(X)
+# define sqlite3BtreeSharable(X) 0
+# define sqlite3BtreeEnterCursor(X)
 #endif
 
 #if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE
-  int sqlite3BtreeSharable(Btree*);
   void sqlite3BtreeLeave(Btree*);
-  void sqlite3BtreeEnterCursor(BtCursor*);
   void sqlite3BtreeLeaveCursor(BtCursor*);
   void sqlite3BtreeLeaveAll(sqlite3*);
 #ifndef NDEBUG
@@ -306,9 +308,7 @@ void sqlite3BtreeCursorList(Btree*);
 #endif
 #else
 
-# define sqlite3BtreeSharable(X) 0
 # define sqlite3BtreeLeave(X)
-# define sqlite3BtreeEnterCursor(X)
 # define sqlite3BtreeLeaveCursor(X)
 # define sqlite3BtreeLeaveAll(X)
 
diff --git a/src/build.c b/src/build.c
index 63e3004657..6aac454172 100644
--- a/src/build.c
+++ b/src/build.c
@@ -24,15 +24,6 @@
 */
 #include "sqliteInt.h"
 
-/*
-** This routine is called when a new SQL statement is beginning to
-** be parsed.  Initialize the pParse structure as needed.
-*/
-void sqlite3BeginParse(Parse *pParse, int explainFlag){
-  pParse->explain = (u8)explainFlag;
-  pParse->nVar = 0;
-}
-
 #ifndef SQLITE_OMIT_SHARED_CACHE
 /*
 ** The TableLock structure is only used by the sqlite3TableLock() and
diff --git a/src/expr.c b/src/expr.c
index d8d36afa54..3be3bf52db 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -461,8 +461,9 @@ Expr *sqlite3ExprAlloc(
       assert( iValue>=0 );
     }
   }
-  pNew = sqlite3DbMallocZero(db, sizeof(Expr)+nExtra);
+  pNew = sqlite3DbMallocRaw(db, sizeof(Expr)+nExtra);
   if( pNew ){
+    memset(pNew, 0, sizeof(Expr));
     pNew->op = (u8)op;
     pNew->iAgg = -1;
     if( pToken ){
diff --git a/src/func.c b/src/func.c
index ad4cf73c31..45bbb35cd8 100644
--- a/src/func.c
+++ b/src/func.c
@@ -567,10 +567,10 @@ static void total_changes(
 ** A structure defining how to do GLOB-style comparisons.
 */
 struct compareInfo {
-  u8 matchAll;
-  u8 matchOne;
-  u8 matchSet;
-  u8 noCase;
+  u8 matchAll;          /* "*" or "%" */
+  u8 matchOne;          /* "?" or "_" */
+  u8 matchSet;          /* "[" or 0 */
+  u8 noCase;            /* true to ignore case differences */
 };
 
 /*
@@ -633,22 +633,14 @@ static int patternCompare(
   const u8 *zPattern,              /* The glob pattern */
   const u8 *zString,               /* The string to compare against the glob */
   const struct compareInfo *pInfo, /* Information about how to do the compare */
-  u32 esc                          /* The escape character */
+  u32 matchOther                   /* The escape char (LIKE) or '[' (GLOB) */
 ){
   u32 c, c2;                       /* Next pattern and input string chars */
   u32 matchOne = pInfo->matchOne;  /* "?" or "_" */
   u32 matchAll = pInfo->matchAll;  /* "*" or "%" */
-  u32 matchOther;                  /* "[" or the escape character */
   u8 noCase = pInfo->noCase;       /* True if uppercase==lowercase */
   const u8 *zEscaped = 0;          /* One past the last escaped input char */
   
-  /* The GLOB operator does not have an ESCAPE clause.  And LIKE does not
-  ** have the matchSet operator.  So we either have to look for one or
-  ** the other, never both.  Hence the single variable matchOther is used
-  ** to store the one we have to look for.
-  */
-  matchOther = esc ? esc : pInfo->matchSet;
-
   while( (c = Utf8Read(zPattern))!=0 ){
     if( c==matchAll ){  /* Match "*" */
       /* Skip over multiple "*" characters in the pattern.  If there
@@ -662,7 +654,7 @@ static int patternCompare(
       if( c==0 ){
         return 1;   /* "*" at the end of the pattern matches */
       }else if( c==matchOther ){
-        if( esc ){
+        if( pInfo->matchSet==0 ){
           c = sqlite3Utf8Read(&zPattern);
           if( c==0 ) return 0;
         }else{
@@ -670,7 +662,7 @@ static int patternCompare(
           ** recursive search in this case, but it is an unusual case. */
           assert( matchOther<0x80 );  /* '[' is a single-byte character */
           while( *zString
-                 && patternCompare(&zPattern[-1],zString,pInfo,esc)==0 ){
+                 && patternCompare(&zPattern[-1],zString,pInfo,matchOther)==0 ){
             SQLITE_SKIP_UTF8(zString);
           }
           return *zString!=0;
@@ -696,18 +688,18 @@ static int patternCompare(
         }
         while( (c2 = *(zString++))!=0 ){
           if( c2!=c && c2!=cx ) continue;
-          if( patternCompare(zPattern,zString,pInfo,esc) ) return 1;
+          if( patternCompare(zPattern,zString,pInfo,matchOther) ) return 1;
         }
       }else{
         while( (c2 = Utf8Read(zString))!=0 ){
           if( c2!=c ) continue;
-          if( patternCompare(zPattern,zString,pInfo,esc) ) return 1;
+          if( patternCompare(zPattern,zString,pInfo,matchOther) ) return 1;
         }
       }
       return 0;
     }
     if( c==matchOther ){
-      if( esc ){
+      if( pInfo->matchSet==0 ){
         c = sqlite3Utf8Read(&zPattern);
         if( c==0 ) return 0;
         zEscaped = zPattern;
@@ -760,7 +752,7 @@ static int patternCompare(
 ** The sqlite3_strglob() interface.
 */
 int sqlite3_strglob(const char *zGlobPattern, const char *zString){
-  return patternCompare((u8*)zGlobPattern, (u8*)zString, &globInfo, 0)==0;
+  return patternCompare((u8*)zGlobPattern, (u8*)zString, &globInfo, '[')==0;
 }
 
 /*
@@ -798,9 +790,10 @@ static void likeFunc(
   sqlite3_value **argv
 ){
   const unsigned char *zA, *zB;
-  u32 escape = 0;
+  u32 escape;
   int nPat;
   sqlite3 *db = sqlite3_context_db_handle(context);
+  struct compareInfo *pInfo = sqlite3_user_data(context);
 
 #ifdef SQLITE_LIKE_DOESNT_MATCH_BLOBS
   if( sqlite3_value_type(argv[0])==SQLITE_BLOB
@@ -840,13 +833,13 @@ static void likeFunc(
       return;
     }
     escape = sqlite3Utf8Read(&zEsc);
+  }else{
+    escape = pInfo->matchSet;
   }
   if( zA && zB ){
-    struct compareInfo *pInfo = sqlite3_user_data(context);
 #ifdef SQLITE_TEST
     sqlite3_like_count++;
 #endif
-    
     sqlite3_result_int(context, patternCompare(zB, zA, pInfo, escape));
   }
 }
diff --git a/src/mem5.c b/src/mem5.c
index 49bebca093..7316a630a6 100644
--- a/src/mem5.c
+++ b/src/mem5.c
@@ -102,6 +102,7 @@ static SQLITE_WSD struct Mem5Global {
   */
   sqlite3_mutex *mutex;
 
+#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
   /*
   ** Performance statistics
   */
@@ -113,6 +114,7 @@ static SQLITE_WSD struct Mem5Global {
   u32 maxOut;         /* Maximum instantaneous currentOut */
   u32 maxCount;       /* Maximum instantaneous currentCount */
   u32 maxRequest;     /* Largest allocation (exclusive of internal frag) */
+#endif
   
   /*
   ** Lists of free blocks.  aiFreelist[0] is a list of free blocks of
@@ -224,14 +226,17 @@ static void *memsys5MallocUnsafe(int nByte){
   /* nByte must be a positive */
   assert( nByte>0 );
 
+  /* No more than 1GiB per allocation */
+  if( nByte > 0x40000000 ) return 0;
+
+#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
   /* Keep track of the maximum allocation request.  Even unfulfilled
   ** requests are counted */
   if( (u32)nByte>mem5.maxRequest ){
-    /* Abort if the requested allocation size is larger than the largest
-    ** power of two that we can represent using 32-bit signed integers. */
-    if( nByte > 0x40000000 ) return 0;
     mem5.maxRequest = nByte;
   }
+#endif
+
 
   /* Round nByte up to the next valid power of two */
   for(iFullSz=mem5.szAtom,iLogsize=0; iFullSz<nByte; iFullSz*=2,iLogsize++){}
@@ -258,6 +263,7 @@ static void *memsys5MallocUnsafe(int nByte){
   }
   mem5.aCtrl[i] = iLogsize;
 
+#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
   /* Update allocator performance statistics. */
   mem5.nAlloc++;
   mem5.totalAlloc += iFullSz;
@@ -266,6 +272,7 @@ static void *memsys5MallocUnsafe(int nByte){
   mem5.currentOut += iFullSz;
   if( mem5.maxCount<mem5.currentCount ) mem5.maxCount = mem5.currentCount;
   if( mem5.maxOut<mem5.currentOut ) mem5.maxOut = mem5.currentOut;
+#endif
 
 #ifdef SQLITE_DEBUG
   /* Make sure the allocated memory does not assume that it is set to zero
@@ -300,12 +307,15 @@ static void memsys5FreeUnsafe(void *pOld){
 
   mem5.aCtrl[iBlock] |= CTRL_FREE;
   mem5.aCtrl[iBlock+size-1] |= CTRL_FREE;
+
+#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
   assert( mem5.currentCount>0 );
   assert( mem5.currentOut>=(size*mem5.szAtom) );
   mem5.currentCount--;
   mem5.currentOut -= size*mem5.szAtom;
   assert( mem5.currentOut>0 || mem5.currentCount==0 );
   assert( mem5.currentCount>0 || mem5.currentOut==0 );
+#endif
 
   mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
   while( ALWAYS(iLogsize<LOGMAX) ){
diff --git a/src/os_unix.c b/src/os_unix.c
index 791ba5d8d9..a40a866780 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -437,26 +437,36 @@ static struct unix_syscall {
 #define osGeteuid   ((uid_t(*)(void))aSyscall[21].pCurrent)
 
 #if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
-  { "mmap",       (sqlite3_syscall_ptr)mmap,     0 },
+  { "mmap",         (sqlite3_syscall_ptr)mmap,            0 },
+#else
+  { "mmap",         (sqlite3_syscall_ptr)0,               0 },
+#endif
 #define osMmap ((void*(*)(void*,size_t,int,int,int,off_t))aSyscall[22].pCurrent)
 
+#if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
   { "munmap",       (sqlite3_syscall_ptr)munmap,          0 },
+#else
+  { "munmap",       (sqlite3_syscall_ptr)0,               0 },
+#endif
 #define osMunmap ((void*(*)(void*,size_t))aSyscall[23].pCurrent)
 
-#if HAVE_MREMAP
+#if HAVE_MREMAP && (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0)
   { "mremap",       (sqlite3_syscall_ptr)mremap,          0 },
 #else
   { "mremap",       (sqlite3_syscall_ptr)0,               0 },
 #endif
 #define osMremap ((void*(*)(void*,size_t,size_t,int,...))aSyscall[24].pCurrent)
 
+#if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
   { "getpagesize",  (sqlite3_syscall_ptr)unixGetpagesize, 0 },
+#else
+  { "getpagesize",  (sqlite3_syscall_ptr)0,               0 },
+#endif
 #define osGetpagesize ((int(*)(void))aSyscall[25].pCurrent)
 
   { "readlink",     (sqlite3_syscall_ptr)readlink,        0 },
 #define osReadlink ((ssize_t(*)(const char*,char*,size_t))aSyscall[26].pCurrent)
 
-#endif
 
 }; /* End of the overrideable system calls */
 
diff --git a/src/parse.y b/src/parse.y
index 6ac2be21f2..d6a587a2c8 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -114,10 +114,10 @@ cmdlist ::= cmdlist ecmd.
 cmdlist ::= ecmd.
 ecmd ::= SEMI.
 ecmd ::= explain cmdx SEMI.
-explain ::= .           { sqlite3BeginParse(pParse, 0); }
+explain ::= .
 %ifndef SQLITE_OMIT_EXPLAIN
-explain ::= EXPLAIN.              { sqlite3BeginParse(pParse, 1); }
-explain ::= EXPLAIN QUERY PLAN.   { sqlite3BeginParse(pParse, 2); }
+explain ::= EXPLAIN.              { pParse->explain = 1; }
+explain ::= EXPLAIN QUERY PLAN.   { pParse->explain = 2; }
 %endif  SQLITE_OMIT_EXPLAIN
 cmdx ::= cmd.           { sqlite3FinishCoding(pParse); }
 
diff --git a/src/pcache.h b/src/pcache.h
index 42c44cf7ba..475c04c061 100644
--- a/src/pcache.h
+++ b/src/pcache.h
@@ -55,6 +55,8 @@ struct PgHdr {
 #define PGHDR_DONT_WRITE      0x020  /* Do not write content to disk */
 #define PGHDR_MMAP            0x040  /* This is an mmap page object */
 
+#define PGHDR_WAL_APPEND      0x080  /* Appended to wal file */
+
 /* Initialize and shutdown the page cache subsystem */
 int sqlite3PcacheInitialize(void);
 void sqlite3PcacheShutdown(void);
diff --git a/src/select.c b/src/select.c
index f8b8e9e77f..b1db07d09a 100644
--- a/src/select.c
+++ b/src/select.c
@@ -111,29 +111,34 @@ Select *sqlite3SelectNew(
   Select *pNew;
   Select standin;
   sqlite3 *db = pParse->db;
-  pNew = sqlite3DbMallocZero(db, sizeof(*pNew) );
+  pNew = sqlite3DbMallocRaw(db, sizeof(*pNew) );
   if( pNew==0 ){
     assert( db->mallocFailed );
     pNew = &standin;
-    memset(pNew, 0, sizeof(*pNew));
   }
   if( pEList==0 ){
     pEList = sqlite3ExprListAppend(pParse, 0, sqlite3Expr(db,TK_ASTERISK,0));
   }
   pNew->pEList = pEList;
+  pNew->op = TK_SELECT;
+  pNew->selFlags = selFlags;
+  pNew->iLimit = 0;
+  pNew->iOffset = 0;
+  pNew->addrOpenEphm[0] = -1;
+  pNew->addrOpenEphm[1] = -1;
+  pNew->nSelectRow = 0;
   if( pSrc==0 ) pSrc = sqlite3DbMallocZero(db, sizeof(*pSrc));
   pNew->pSrc = pSrc;
   pNew->pWhere = pWhere;
   pNew->pGroupBy = pGroupBy;
   pNew->pHaving = pHaving;
   pNew->pOrderBy = pOrderBy;
-  pNew->selFlags = selFlags;
-  pNew->op = TK_SELECT;
+  pNew->pPrior = 0;
+  pNew->pNext = 0;
   pNew->pLimit = pLimit;
   pNew->pOffset = pOffset;
+  pNew->pWith = 0;
   assert( pOffset==0 || pLimit!=0 || pParse->nErr>0 || db->mallocFailed!=0 );
-  pNew->addrOpenEphm[0] = -1;
-  pNew->addrOpenEphm[1] = -1;
   if( db->mallocFailed ) {
     clearSelect(db, pNew, pNew!=&standin);
     pNew = 0;
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index c01bbc7869..a4d4f65f3c 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -767,10 +767,6 @@ typedef INT16_TYPE LogEst;
 */
 #ifdef __APPLE__
 # include <TargetConditionals.h>
-# if TARGET_OS_IPHONE
-#   undef SQLITE_MAX_MMAP_SIZE
-#   define SQLITE_MAX_MMAP_SIZE 0
-# endif
 #endif
 #ifndef SQLITE_MAX_MMAP_SIZE
 # if defined(__linux__) \
@@ -3340,7 +3336,6 @@ void sqlite3Pragma(Parse*,Token*,Token*,Token*,int);
 void sqlite3ResetAllSchemasOfConnection(sqlite3*);
 void sqlite3ResetOneSchema(sqlite3*,int);
 void sqlite3CollapseDatabaseArray(sqlite3*);
-void sqlite3BeginParse(Parse*,int);
 void sqlite3CommitInternalChanges(sqlite3*);
 void sqlite3DeleteColumnNames(sqlite3*,Table*);
 int sqlite3ColumnsFromExprList(Parse*,ExprList*,i16*,Column**);
diff --git a/src/tclsqlite.c b/src/tclsqlite.c
index f024317e90..604e898265 100644
--- a/src/tclsqlite.c
+++ b/src/tclsqlite.c
@@ -2976,6 +2976,10 @@ static int DbMain(void *cd, Tcl_Interp *interp, int objc,Tcl_Obj *const*objv){
       Tcl_AppendResult(interp,sqlite3_libversion(), (char*)0);
       return TCL_OK;
     }
+    if( strcmp(zArg,"-sourceid")==0 ){
+      Tcl_AppendResult(interp,sqlite3_sourceid(), (char*)0);
+      return TCL_OK;
+    }
     if( strcmp(zArg,"-has-codec")==0 ){
 #ifdef SQLITE_HAS_CODEC
       Tcl_AppendResult(interp,"1",(char*)0);
diff --git a/src/vdbe.c b/src/vdbe.c
index 5acb3b3137..7eb4c0baeb 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -2374,7 +2374,6 @@ case OP_Column: {
   u64 offset64;      /* 64-bit offset */
   u32 avail;         /* Number of bytes of available data */
   u32 t;             /* A type code from the record header */
-  u16 fx;            /* pDest->flags value */
   Mem *pReg;         /* PseudoTable input register */
 
   p2 = pOp->p2;
@@ -2552,10 +2551,31 @@ case OP_Column: {
   assert( sqlite3VdbeCheckMemInvariants(pDest) );
   if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
   assert( t==pC->aType[p2] );
+  pDest->enc = encoding;
   if( pC->szRow>=aOffset[p2+1] ){
     /* This is the common case where the desired content fits on the original
     ** page - where the content is not on an overflow page */
-    sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], t, pDest);
+    zData = pC->aRow + aOffset[p2];
+    if( t<12 ){
+      sqlite3VdbeSerialGet(zData, t, pDest);
+    }else{
+      /* If the column value is a string, we need a persistent value, not
+      ** a MEM_Ephem value.  This branch is a fast short-cut that is equivalent
+      ** to calling sqlite3VdbeSerialGet() and sqlite3VdbeDeephemeralize().
+      */
+      static const u16 aFlag[] = { MEM_Blob, MEM_Str|MEM_Term };
+      pDest->n = len = (t-12)/2;
+      if( pDest->szMalloc < len+2 ){
+        pDest->flags = MEM_Null;
+        if( sqlite3VdbeMemGrow(pDest, len+2, 0) ) goto no_mem;
+      }else{
+        pDest->z = pDest->zMalloc;
+      }
+      memcpy(pDest->z, zData, len);
+      pDest->z[len] = 0;
+      pDest->z[len+1] = 0;
+      pDest->flags = aFlag[t&1];
+    }
   }else{
     /* This branch happens only when content is on overflow pages */
     if( ((pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
@@ -2567,38 +2587,20 @@ case OP_Column: {
       **    2. the length(X) function if X is a blob, and
       **    3. if the content length is zero.
       ** So we might as well use bogus content rather than reading
-      ** content from disk.  NULL will work for the value for strings
-      ** and blobs and whatever is in the payloadSize64 variable
-      ** will work for everything else. */
-      sqlite3VdbeSerialGet(t<=13 ? (u8*)&payloadSize64 : 0, t, pDest);
+      ** content from disk. */
+      static u8 aZero[8];  /* This is the bogus content */
+      sqlite3VdbeSerialGet(aZero, t, pDest);
     }else{
       rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, !pC->isTable,
                                    pDest);
-      if( rc!=SQLITE_OK ){
-        goto op_column_error;
+      if( rc==SQLITE_OK ){
+        sqlite3VdbeSerialGet((const u8*)pDest->z, t, pDest);
+        pDest->flags &= ~MEM_Ephem;
       }
-      sqlite3VdbeSerialGet((const u8*)pDest->z, t, pDest);
-      pDest->flags &= ~MEM_Ephem;
     }
   }
-  pDest->enc = encoding;
 
 op_column_out:
-  /* If the column value is an ephemeral string, go ahead and persist
-  ** that string in case the cursor moves before the column value is
-  ** used.  The following code does the equivalent of Deephemeralize()
-  ** but does it faster. */
-  if( (pDest->flags & MEM_Ephem)!=0 && pDest->z ){
-    fx = pDest->flags & (MEM_Str|MEM_Blob);
-    assert( fx!=0 );
-    zData = (const u8*)pDest->z;
-    len = pDest->n;
-    if( sqlite3VdbeMemClearAndResize(pDest, len+2) ) goto no_mem;
-    memcpy(pDest->z, zData, len);
-    pDest->z[len] = 0;
-    pDest->z[len+1] = 0;
-    pDest->flags = fx|MEM_Term;
-  }
 op_column_error:
   UPDATE_MAX_BLOBSIZE(pDest);
   REGISTER_TRACE(pOp->p3, pDest);
diff --git a/src/vdbeInt.h b/src/vdbeInt.h
index d1de55eb1c..b231cf908e 100644
--- a/src/vdbeInt.h
+++ b/src/vdbeInt.h
@@ -489,11 +489,15 @@ int sqlite3VdbeSorterRewind(const VdbeCursor *, int *);
 int sqlite3VdbeSorterWrite(const VdbeCursor *, Mem *);
 int sqlite3VdbeSorterCompare(const VdbeCursor *, Mem *, int, int *);
 
-#if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
+#if !defined(SQLITE_OMIT_SHARED_CACHE) 
   void sqlite3VdbeEnter(Vdbe*);
-  void sqlite3VdbeLeave(Vdbe*);
 #else
 # define sqlite3VdbeEnter(X)
+#endif
+
+#if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
+  void sqlite3VdbeLeave(Vdbe*);
+#else
 # define sqlite3VdbeLeave(X)
 #endif
 
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index dbbb2a6ccb..aa8070a132 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -1317,7 +1317,7 @@ void sqlite3VdbeUsesBtree(Vdbe *p, int i){
   }
 }
 
-#if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
+#if !defined(SQLITE_OMIT_SHARED_CACHE)
 /*
 ** If SQLite is compiled to support shared-cache mode and to be threadsafe,
 ** this routine obtains the mutex associated with each BtShared structure
diff --git a/src/wal.c b/src/wal.c
index 4238ea483b..ae6a54849a 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -445,6 +445,7 @@ struct Wal {
   u8 padToSectorBoundary;    /* Pad transactions out to the next sector */
   WalIndexHdr hdr;           /* Wal-index header for current transaction */
   u32 minFrame;              /* Ignore wal frames before this one */
+  u32 iReCksum;              /* On commit, recalculate checksums from here */
   const char *zWalName;      /* Name of WAL file */
   u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
 #ifdef SQLITE_DEBUG
@@ -698,14 +699,16 @@ static void walEncodeFrame(
   assert( WAL_FRAME_HDRSIZE==24 );
   sqlite3Put4byte(&aFrame[0], iPage);
   sqlite3Put4byte(&aFrame[4], nTruncate);
-  memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
+  if( pWal->iReCksum==0 ){
+    memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
 
-  nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
-  walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
-  walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
+    nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
+    walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
+    walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
 
-  sqlite3Put4byte(&aFrame[16], aCksum[0]);
-  sqlite3Put4byte(&aFrame[20], aCksum[1]);
+    sqlite3Put4byte(&aFrame[16], aCksum[0]);
+    sqlite3Put4byte(&aFrame[20], aCksum[1]);
+  }
 }
 
 /*
@@ -2632,6 +2635,7 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
   /* Cannot start a write transaction without first holding a read
   ** transaction. */
   assert( pWal->readLock>=0 );
+  assert( pWal->writeLock==0 && pWal->iReCksum==0 );
 
   if( pWal->readOnly ){
     return SQLITE_READONLY;
@@ -2667,6 +2671,7 @@ int sqlite3WalEndWriteTransaction(Wal *pWal){
   if( pWal->writeLock ){
     walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
     pWal->writeLock = 0;
+    pWal->iReCksum = 0;
     pWal->truncateOnCommit = 0;
   }
   return SQLITE_OK;
@@ -2885,6 +2890,59 @@ static int walWriteOneFrame(
   return rc;
 }
 
+/*
+** This function is called as part of committing a transaction within which
+** one or more frames have been overwritten. It updates the checksums for
+** all frames written to the wal file by the current transaction starting
+** with the earliest to have been overwritten.
+**
+** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
+*/
+static int walRewriteChecksums(Wal *pWal, u32 iLast){
+  const int szPage = pWal->szPage;/* Database page size */
+  int rc = SQLITE_OK;             /* Return code */
+  u8 *aBuf;                       /* Buffer to load data from wal file into */
+  u8 aFrame[WAL_FRAME_HDRSIZE];   /* Buffer to assemble frame-headers in */
+  u32 iRead;                      /* Next frame to read from wal file */
+  i64 iCksumOff;
+
+  aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE);
+  if( aBuf==0 ) return SQLITE_NOMEM;
+
+  /* Find the checksum values to use as input for the recalculating the
+  ** first checksum. If the first frame is frame 1 (implying that the current
+  ** transaction restarted the wal file), these values must be read from the
+  ** wal-file header. Otherwise, read them from the frame header of the
+  ** previous frame.  */
+  assert( pWal->iReCksum>0 );
+  if( pWal->iReCksum==1 ){
+    iCksumOff = 24;
+  }else{
+    iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16;
+  }
+  rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff);
+  pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf);
+  pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]);
+
+  iRead = pWal->iReCksum;
+  pWal->iReCksum = 0;
+  for(; rc==SQLITE_OK && iRead<=iLast; iRead++){
+    i64 iOff = walFrameOffset(iRead, szPage);
+    rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff);
+    if( rc==SQLITE_OK ){
+      u32 iPgno, nDbSize;
+      iPgno = sqlite3Get4byte(aBuf);
+      nDbSize = sqlite3Get4byte(&aBuf[4]);
+
+      walEncodeFrame(pWal, iPgno, nDbSize, &aBuf[WAL_FRAME_HDRSIZE], aFrame);
+      rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOff);
+    }
+  }
+
+  sqlite3_free(aBuf);
+  return rc;
+}
+
 /* 
 ** Write a set of frames to the log. The caller must hold the write-lock
 ** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
@@ -2905,6 +2963,8 @@ int sqlite3WalFrames(
   int szFrame;                    /* The size of a single frame */
   i64 iOffset;                    /* Next byte to write in WAL file */
   WalWriter w;                    /* The writer */
+  u32 iFirst = 0;                 /* First frame that may be overwritten */
+  WalIndexHdr *pLive;             /* Pointer to shared header */
 
   assert( pList );
   assert( pWal->writeLock );
@@ -2920,6 +2980,11 @@ int sqlite3WalFrames(
   }
 #endif
 
+  pLive = (WalIndexHdr*)walIndexHdr(pWal);
+  if( memcmp(&pWal->hdr, (void *)pLive, sizeof(WalIndexHdr))!=0 ){
+    iFirst = pLive->mxFrame+1;
+  }
+
   /* See if it is possible to write these frames into the start of the
   ** log file, instead of appending to it at pWal->hdr.mxFrame.
   */
@@ -2984,6 +3049,27 @@ int sqlite3WalFrames(
   /* Write all frames into the log file exactly once */
   for(p=pList; p; p=p->pDirty){
     int nDbSize;   /* 0 normally.  Positive == commit flag */
+
+    /* Check if this page has already been written into the wal file by
+    ** the current transaction. If so, overwrite the existing frame and
+    ** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that 
+    ** checksums must be recomputed when the transaction is committed.  */
+    if( iFirst && (p->pDirty || isCommit==0) ){
+      u32 iWrite = 0;
+      VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite);
+      assert( rc==SQLITE_OK || iWrite==0 );
+      if( iWrite>=iFirst ){
+        i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE;
+        if( pWal->iReCksum==0 || iWrite<pWal->iReCksum ){
+          pWal->iReCksum = iWrite;
+        }
+        rc = sqlite3OsWrite(pWal->pWalFd, p->pData, szPage, iOff);
+        if( rc ) return rc;
+        p->flags &= ~PGHDR_WAL_APPEND;
+        continue;
+      }
+    }
+
     iFrame++;
     assert( iOffset==walFrameOffset(iFrame, szPage) );
     nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0;
@@ -2991,6 +3077,13 @@ int sqlite3WalFrames(
     if( rc ) return rc;
     pLast = p;
     iOffset += szFrame;
+    p->flags |= PGHDR_WAL_APPEND;
+  }
+
+  /* Recalculate checksums within the wal file if required. */
+  if( isCommit && pWal->iReCksum ){
+    rc = walRewriteChecksums(pWal, iFrame);
+    if( rc ) return rc;
   }
 
   /* If this is the end of a transaction, then we might need to pad
@@ -3042,6 +3135,7 @@ int sqlite3WalFrames(
   */
   iFrame = pWal->hdr.mxFrame;
   for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){
+    if( (p->flags & PGHDR_WAL_APPEND)==0 ) continue;
     iFrame++;
     rc = walIndexAppend(pWal, iFrame, p->pgno);
   }
@@ -3154,6 +3248,7 @@ int sqlite3WalCheckpoint(
 
   /* Copy data from the log to the database file. */
   if( rc==SQLITE_OK ){
+
     if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
       rc = SQLITE_CORRUPT_BKPT;
     }else{
diff --git a/src/walker.c b/src/walker.c
index 81e0f2cd60..1e0ad32871 100644
--- a/src/walker.c
+++ b/src/walker.c
@@ -36,9 +36,8 @@
 ** The return value from this routine is WRC_Abort to abandon the tree walk
 ** and WRC_Continue to continue.
 */
-int sqlite3WalkExpr(Walker *pWalker, Expr *pExpr){
+static SQLITE_NOINLINE int walkExpr(Walker *pWalker, Expr *pExpr){
   int rc;
-  if( pExpr==0 ) return WRC_Continue;
   testcase( ExprHasProperty(pExpr, EP_TokenOnly) );
   testcase( ExprHasProperty(pExpr, EP_Reduced) );
   rc = pWalker->xExprCallback(pWalker, pExpr);
@@ -54,6 +53,9 @@ int sqlite3WalkExpr(Walker *pWalker, Expr *pExpr){
   }
   return rc & WRC_Abort;
 }
+int sqlite3WalkExpr(Walker *pWalker, Expr *pExpr){
+  return pExpr ? walkExpr(pWalker,pExpr) : WRC_Continue;
+}
 
 /*
 ** Call sqlite3WalkExpr() for every expression in list p or until
diff --git a/test/tester.tcl b/test/tester.tcl
index 4008a34491..426808ea90 100644
--- a/test/tester.tcl
+++ b/test/tester.tcl
@@ -1028,7 +1028,13 @@ proc finalize_testing {} {
     output2 "[expr {$nErr-$nKnown}] new errors and $nKnown known errors\
          out of $nTest tests"
   } else {
-    output2 "$nErr errors out of $nTest tests"
+    set cpuinfo {}
+    if {[catch {exec hostname} hname]==0} {set cpuinfo [string trim $hname]}
+    append cpuinfo " $::tcl_platform(os)"
+    append cpuinfo " [expr {$::tcl_platform(pointerSize)*8}]-bit"
+    append cpuinfo " [string map {E -e} $::tcl_platform(byteOrder)]"
+    output2 "SQLite [sqlite3 -sourceid]"
+    output2 "$nErr errors out of $nTest tests on $cpuinfo"
   }
   if {$nErr>$nKnown} {
     output2 -nonewline "!Failures on these tests:"
diff --git a/test/vtabH.test b/test/vtabH.test
index 7bd542e05b..d16db13674 100644
--- a/test/vtabH.test
+++ b/test/vtabH.test
@@ -68,19 +68,19 @@ set x7 backbone
 set x8 backarrow
 set x9 castle
 
-db func glob gfunc
+db func glob -argcount 2 gfunc
 proc gfunc {a b} {
   incr ::gfunc
   return 1
 }
 
-db func like lfunc
+db func like -argcount 2 lfunc
 proc lfunc {a b} {
   incr ::gfunc 100
   return 1
 }
 
-db func regexp rfunc
+db func regexp -argcount 2 rfunc
 proc rfunc {a b} {
   incr ::gfunc 10000
   return 1
diff --git a/test/wal.test b/test/wal.test
index bfe3634577..abd3a3ce49 100644
--- a/test/wal.test
+++ b/test/wal.test
@@ -712,7 +712,7 @@ do_test wal-11.5 {
 do_test wal-11.6 {
   execsql COMMIT
   list [expr [file size test.db]/1024] [file size test.db-wal]
-} [list 3 [wal_file_size 41 1024]]
+} [list 3 [wal_file_size 40 1024]]
 do_test wal-11.7 {
   execsql { 
     SELECT count(*) FROM t1;
@@ -722,15 +722,22 @@ do_test wal-11.7 {
 do_test wal-11.8 {
   execsql { PRAGMA wal_checkpoint }
   list [expr [file size test.db]/1024] [file size test.db-wal]
-} [list 37 [wal_file_size 41 1024]]
+} [list 37 [wal_file_size 40 1024]]
 do_test wal-11.9 {
   db close
   list [expr [file size test.db]/1024] [log_deleted test.db-wal]
 } {37 1}
 sqlite3_wal db test.db
-set nWal 39
-if {[permutation]!="mmap"} {set nWal 37}
-ifcapable !mmap {set nWal 37}
+
+# After adding the capability of WAL to overwrite prior uncommitted
+# frame in the WAL-file with revised content, the size of the WAL file
+# following cache-spill is smaller.
+#
+#set nWal 39
+#if {[permutation]!="mmap"} {set nWal 37}
+#ifcapable !mmap {set nWal 37}
+set nWal 34
+
 do_test wal-11.10 {
   execsql {
     PRAGMA cache_size = 10;
diff --git a/test/waloverwrite.test b/test/waloverwrite.test
new file mode 100644
index 0000000000..5e51a70d3f
--- /dev/null
+++ b/test/waloverwrite.test
@@ -0,0 +1,164 @@
+# 2010 May 5
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library.  The
+# focus of this file is testing the operation of the library in
+# "PRAGMA journal_mode=WAL" mode.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+source $testdir/wal_common.tcl
+set testprefix waloverwrite
+
+ifcapable !wal {finish_test ; return }
+
+# Simple test:
+#
+# Test cases *.1 - *.6:
+#
+#   + Create a database of blobs roughly 50 pages in size.
+#
+#   + Set the db cache size to something much smaller than this (5 pages)
+#
+#   + Within a transaction, loop through the set of blobs 5 times. Update
+#      each blob as it is visited.
+#
+#   + Test that the wal file is roughly 50 pages in size - even though many
+#      database pages have been written to it multiple times.
+#
+#   + Take a copy of the database and wal file. Test that recovery can
+#     be run on it.
+#
+# Test cases *.7 - *.9:
+#
+#   + Same thing, but before committing the statement transaction open
+#     a SAVEPOINT, update the blobs another 5 times, then roll it back.
+#
+#   + Check that if recovery is run on the resulting wal file, the rolled
+#     back changes from within the SAVEPOINT are not present in the db.
+#
+# The above is run twice - once where the wal file is empty at the start of
+# step 3 (tn==1) and once where it already contains a transaction (tn==2).
+#
+foreach {tn xtra} {
+  1 {}
+  2 { UPDATE t1 SET y = randomblob(799) WHERE x=4 }
+} {
+  reset_db
+  do_execsql_test 1.$tn.0 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(x, y);
+    CREATE INDEX i1y ON t1(y);
+  
+    WITH cnt(i) AS (
+      SELECT 1 UNION ALL SELECT i+1 FROM cnt WHERE i<20
+    )
+    INSERT INTO t1 SELECT i, randomblob(800) FROM cnt;
+  } {}
+  
+  do_test 1.$tn.1 {
+    set nPg [db one { PRAGMA page_count } ]
+    expr $nPg>40 && $nPg<50
+  } {1}
+  
+  do_test 1.$tn.2 {
+    db close
+    sqlite3 db test.db
+  
+    execsql {PRAGMA journal_mode = wal}
+    execsql {PRAGMA cache_size = 5}
+    execsql $xtra
+  
+    db transaction {
+      for {set i 0} {$i < 5} {incr i} {
+        foreach x [db eval {SELECT x FROM t1}] {
+          execsql { UPDATE t1 SET y = randomblob(799) WHERE x=$x }
+        }
+      }
+    }
+  
+    set nPg [wal_frame_count test.db-wal 1024]
+    expr $nPg>40 && $nPg<60
+  } {1}
+  
+  do_execsql_test 1.$tn.3 { PRAGMA integrity_check } ok
+  
+  do_test 1.$tn.4 {
+    forcedelete test.db2 test.db2-wal
+    forcecopy test.db test.db2
+    sqlite3 db2 test.db2
+    execsql { SELECT sum(length(y)) FROM t1 } db2
+  } [expr 20*800]
+  
+  do_test 1.$tn.5 {
+    db2 close
+    forcecopy test.db test.db2
+    forcecopy test.db-wal test.db2-wal
+    sqlite3 db2 test.db2
+    execsql { SELECT sum(length(y)) FROM t1 } db2
+  } [expr 20*799]
+  
+  do_test 1.$tn.6 {
+    execsql { PRAGMA integrity_check } db2
+  } ok
+  db2 close
+
+  do_test 1.$tn.7 {
+    execsql { PRAGMA wal_checkpoint }
+    db transaction {
+      for {set i 0} {$i < 1} {incr i} {
+        foreach x [db eval {SELECT x FROM t1}] {
+          execsql { UPDATE t1 SET y = randomblob(798) WHERE x=$x }
+        }
+      }
+
+      execsql {
+        WITH cnt(i) AS (SELECT 1 UNION ALL SELECT i+1 FROM cnt WHERE i<20)
+        INSERT INTO t2 SELECT i, randomblob(800) FROM cnt;
+      }
+
+      execsql {SAVEPOINT abc}
+      for {set i 0} {$i < 5} {incr i} {
+        foreach x [db eval {SELECT x FROM t1}] {
+          execsql { UPDATE t1 SET y = randomblob(797) WHERE x=$x }
+        }
+      }
+      breakpoint
+      execsql {ROLLBACK TO abc}
+
+    }
+
+    set nPg [wal_frame_count test.db-wal 1024]
+    expr $nPg>55 && $nPg<75
+  } {1}
+
+  do_test 1.$tn.8 {
+    forcedelete test.db2 test.db2-wal
+    forcecopy test.db test.db2
+    sqlite3 db2 test.db2
+    execsql { SELECT sum(length(y)) FROM t1 } db2
+  } [expr 20*799]
+
+  do_test 1.$tn.9 {
+    db2 close
+    forcecopy test.db-wal test.db2-wal
+    sqlite3 db2 test.db2
+    execsql { SELECT sum(length(y)) FROM t1 } db2
+  } [expr 20*798]
+
+  do_test 1.$tn.9 {
+    execsql { PRAGMA integrity_check } db2
+  } ok
+  db2 close
+}
+
+finish_test
+