diff --git a/ext/fts3/fts3_porter.c b/ext/fts3/fts3_porter.c
index db175acdbb..8fb4c25daa 100644
--- a/ext/fts3/fts3_porter.c
+++ b/ext/fts3/fts3_porter.c
@@ -183,7 +183,7 @@ static int isVowel(const char *z){
 ** by a consonant.
 **
 ** In this routine z[] is in reverse order.  So we are really looking
-** for an instance of of a consonant followed by a vowel.
+** for an instance of a consonant followed by a vowel.
 */
 static int m_gt_0(const char *z){
   while( isVowel(z) ){ z++; }
diff --git a/manifest b/manifest
index f563572da1..6ebd011b87 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Merge\sall\srecent\sfixes\sand\senhancements\sfrom\strunk\sinto\ssessions.
-D 2014-12-02T16:31:01.447
+C Incorporate\sthe\sSQLITE_CHECKPOINT_TRUNCATE\senhancement\sand\sa\scouple\sof\nobscure\sbug\sfixes\sfrom\strunk.
+D 2014-12-04T23:35:08.510
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in e2007fafb7b679a39800a1d636dcc6662a840530
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -86,7 +86,7 @@ F ext/fts3/fts3_expr.c 40123785eaa3ebd4c45c9b23407cc44ac0c49905
 F ext/fts3/fts3_hash.c 29b986e43f4e9dd40110eafa377dc0d63c422c60
 F ext/fts3/fts3_hash.h 39cf6874dc239d6b4e30479b1975fe5b22a3caaf
 F ext/fts3/fts3_icu.c e319e108661147bcca8dd511cd562f33a1ba81b5
-F ext/fts3/fts3_porter.c 7f8b4bf5af7c0f20f73b8e87e14fa9298f52e290
+F ext/fts3/fts3_porter.c 3565faf04b626cddf85f03825e86056a4562c009
 F ext/fts3/fts3_snippet.c 51beb5c1498176fd9caccaf1c75b55cb803a985a
 F ext/fts3/fts3_term.c a521f75132f9a495bdca1bdd45949b3191c52763
 F ext/fts3/fts3_test.c 8a3a78c4458b2d7c631fcf4b152a5cd656fa7038
@@ -199,7 +199,7 @@ F src/complete.c c4ba6e0626bb94bc77a0861735f3382fcf7cc818
 F src/ctime.c df19848891c8a553c80e6f5a035e768280952d1a
 F src/date.c 93594514aae68de117ca4a2a0d6cc63eddf26744
 F src/delete.c 20a360262b62051afacb44122b3593a8bd9be131
-F src/expr.c 73de4c0da2eed6b149d40a05c589dfeb2c4a87a1
+F src/expr.c 00da3072f362b06f39ce4052baa1d4ce2bb36d1c
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c da985ae673efef2c712caef825a5d2edb087ead7
 F src/func.c 6d3c4ebd72aa7923ce9b110a7dc15f9b8c548430
@@ -212,7 +212,7 @@ F src/journal.c b4124532212b6952f42eb2c12fa3c25701d8ba8d
 F src/legacy.c ba1863ea58c4c840335a84ec276fc2b25e22bc4e
 F src/lempar.c 7274c97d24bb46631e504332ccd3bd1b37841770
 F src/loadext.c de741e66e5ddc1598d904d7289239696e40ed994
-F src/main.c e8d76c9dc47ae7aac2bb1b3d65b55cea4fdc900f
+F src/main.c 962eac230ec5c619ebccafa498bcfb617af0cc79
 F src/malloc.c 740db54387204c9a2eb67c6d98e68b08e9ef4eab
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c faf615aafd8be74a71494dfa027c113ea5c6615f
@@ -233,29 +233,29 @@ F src/os_setup.h c9d4553b5aaa6f73391448b265b89bed0b890faa
 F src/os_unix.c fb587121840f690101336879adfa6d0b2cd0e8c7
 F src/os_win.c a9e500dd963fb1f67d7860e58b5772abe6123862
 F src/os_win.h 09e751b20bbc107ffbd46e13555dc73576d88e21
-F src/pager.c b8764f90c135482988268eec93d7f5cdb89d687a
+F src/pager.c 7a5c5bc0e29b9b16834f5558a9d5d22bbae59a08
 F src/pager.h d1eee3c3f741be247ce6d82752a178515fc8578b
 F src/parse.y 5dfead8aed90cb0c7c1115898ee2266804daff45
 F src/pcache.c ace1b67632deeaa84859b4c16c27711dfb7db3d4
 F src/pcache.h b44658c9c932d203510279439d891a2a83e12ba8
 F src/pcache1.c facbdd3ecc09c8f750089d941305694301328e98
-F src/pragma.c 3f3e959390a10c0131676f0e307acce372777e0f
+F src/pragma.c d54cdd40b63d608f2d95b7482c710690e3593a73
 F src/prepare.c b7b7bf020bd4c962f7c8aed5a3c542c7dfe9f9c7
 F src/printf.c 9e75a6a0b55bf61cfff7d7e19d89834a1b938236
 F src/random.c ba2679f80ec82c4190062d756f22d0c358180696
-F src/resolve.c 4965007d6497b6a4d7a6d98751cc39712885f952
+F src/resolve.c f6c46d3434439ab2084618d603e6d6dbeb0d6ada
 F src/rowset.c eccf6af6d620aaa4579bd3b72c1b6395d9e9fa1e
-F src/select.c 428165951748151e87a15295b7357221433e311b
+F src/select.c f377fb8a5c73c10678ea74f3400f7913943e3d75
 F src/shell.c 81e4f2b57396db0714bc73d1f95cf3970f5dcc10
-F src/sqlite.h.in 76626596dabd96d98b3bb88495386b1bb5fa7f44
+F src/sqlite.h.in 9e505658e72a84604b7571b6bc78d8a9bde0a9b7
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h 17d487c3c91b0b8c584a32fbeb393f6f795eea7d
-F src/sqliteInt.h 4ad823ef8e31448ca333eafa1892ab35759ae6c1
+F src/sqliteInt.h aff67183ad2b5d29f71a3084e15d16cae96f622c
 F src/sqliteLimit.h 164b0e6749d31e0daa1a4589a169d31c0dec7b3d
 F src/status.c 81712116e826b0089bb221b018929536b2b5406f
 F src/table.c f142bba7903e93ca8d113a5b8877a108ad1a27dc
 F src/tclsqlite.c 05be57620509060e85064b9495256c05d56e76b0
-F src/test1.c a0bce4f47da65b76c80e5f8bf9a5ef174603866a
+F src/test1.c f5d7ecd3dd663b11f35269fd91f7090db0570903
 F src/test2.c 98049e51a17dc62606a99a9eb95ee477f9996712
 F src/test3.c 1c0e5d6f080b8e33c1ce8b3078e7013fdbcd560c
 F src/test4.c 9b32d22f5f150abe23c1830e2057c4037c45b3df
@@ -308,7 +308,7 @@ F src/update.c d207deb7a031f698104bee879de0632b611e72dd
 F src/utf.c fc6b889ba0779b7722634cdeaa25f1930d93820c
 F src/util.c 3b627daa45c7308c1e36e3dbaa3f9ce7e5c7fa73
 F src/vacuum.c 9b30ec729337dd012ed88d4c292922c8ef9cf00c
-F src/vdbe.c 24e590213c0b5b4432db922fcc2981d918b6607d
+F src/vdbe.c c02217423a807dc97c743f5fff493cd55dffa77d
 F src/vdbe.h b434bb75fbec973d18d49225a59833ae39ee2afc
 F src/vdbeInt.h dc69f0351bef56456fdba3e09d3387ba4f1b1520
 F src/vdbeapi.c 3d4d2a2b24055ce2cb029fa73067c56616264b51
@@ -318,10 +318,10 @@ F src/vdbemem.c 96e41193b4affd9ebc0eea2fa628879dac88c744
 F src/vdbesort.c 42c166f7ca78cb643c7f4e4bdfa83c59d363d1a6
 F src/vdbetrace.c 7e4222955e07dd707a2f360c0eb73452be1cb010
 F src/vtab.c c08ec66f45919eaa726bf88aa53eb08379d607f9
-F src/wal.c 486e644b3b8aa5ad066f625bc428aa8ff7001405
+F src/wal.c 847692349eb6e1fb8543dbc97e69ddbfa4cc7ea7
 F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
 F src/walker.c c253b95b4ee44b21c406e2a1052636c31ea27804
-F src/where.c a0b16f9d78321cb340a977287d19f826555c7d3b
+F src/where.c d67fe69dd1bb32ad3d488a8c5bc803a29814f357
 F src/whereInt.h d3633e9b592103241b74b0ec76185f3e5b8b62e0
 F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
 F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
@@ -471,7 +471,7 @@ F test/descidx1.test 6d03b44c8538fe0eb4924e19fba10cdd8f3c9240
 F test/descidx2.test 9f1a0c83fd57f8667c82310ca21b30a350888b5d
 F test/descidx3.test 09ddbe3f5295f482d2f8b687cf6db8bad7acd9a2
 F test/diskfull.test 106391384780753ea6896b7b4f005d10e9866b6e
-F test/distinct.test 086e70c765f172e8974e9f83b9ac5ca03c154e77
+F test/distinct.test 175d49ee783febaf368192dfe7f5afbc68910230
 F test/distinctagg.test 1a6ef9c87a58669438fc771450d7a72577417376
 F test/e_blobbytes.test 9bea1d3e2b20f3010b04abba58f6ba172301f49f
 F test/e_blobclose.test df756753f571bc30e42e3a6cba2807576e49e716
@@ -687,7 +687,7 @@ F test/join.test 52d4d49f86d0cf46926672878c4eaf0da399104a
 F test/join2.test f2171c265e57ee298a27e57e7051d22962f9f324
 F test/join3.test 6f0c774ff1ba0489e6c88a3e77b9d3528fb4fda0
 F test/join4.test 1a352e4e267114444c29266ce79e941af5885916
-F test/join5.test 86675fc2919269aa923c84dd00ee4249b97990fe
+F test/join5.test 5df23eba184f159ed9705a954957e765a10c141d
 F test/join6.test cfe6503791ceb0cbb509966740286ec423cbf10b
 F test/journal1.test 69abc726c51b4a0409189f9a85191205297c0577
 F test/journal2.test ae06f566c28552c313ded3fee79a6c69e6d049b1
@@ -1131,7 +1131,7 @@ F test/wal.test 885f32b2b390b30b4aa3dbb0e568f8f78d40f5cc
 F test/wal2.test 1f841d2048080d32f552942e333fd99ce541dada
 F test/wal3.test b22eb662bcbc148c5f6d956eaf94b047f7afe9c0
 F test/wal4.test 4744e155cd6299c6bd99d3eab1c82f77db9cdb3c
-F test/wal5.test 8f888b50f66b78821e61ed0e233ded5de378224b
+F test/wal5.test 174cc1512e304a7dfa28ac30527e28ea02fc37df
 F test/wal6.test 527581f5527bf9c24394991e2be83000aace5f9e
 F test/wal64k.test 163655ecd2cb8afef4737cac2a40fdd2eeaf20b8
 F test/wal7.test 2ae8f427d240099cc4b2dfef63cff44e2a68a1bd
@@ -1172,7 +1172,7 @@ F test/whereF.test 5b2ba0dbe8074aa13e416b37c753991f0a2492d7
 F test/whereG.test 69f5ec4b15760a8c860f80e2d55525669390aab3
 F test/whereH.test e4b07f7a3c2f5d31195cd33710054c78667573b2
 F test/whereI.test 1d89199697919d4930be05a71e7fe620f114e622
-F test/whereJ.test 63599653dfefe4e74ebb358db753417fe0aa8a49
+F test/whereJ.test 55a3221706a7ab706293f17cc8f96da563bf0767
 F test/wherelimit.test 5e9fd41e79bb2b2d588ed999d641d9c965619b31
 F test/wild001.test bca33f499866f04c24510d74baf1e578d4e44b1c
 F test/win32heap.test ea19770974795cff26e11575e12d422dbd16893c
@@ -1241,7 +1241,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P f09055f3c4348264c7336f90646375f0d98b061e 61b31e771430f490fc2c4cef55046debc4a5f4f5
-R 4cb97995ea5a95cf1669fe4c63af9fe5
+P 2617d93713d9f4cf907ab2e7baef6a0f74f7198e 0d3aef97ebddf422b8bdcbc5878970c6129e3f54
+R 6c3870353869dc63de6b6e7262754990
 U drh
-Z 1bc55c89abd689844735dcd7c551f20d
+Z 0421768e128ea5c34e2d7a186ce23ac0
diff --git a/manifest.uuid b/manifest.uuid
index af77bccc43..b765ac2f7d 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-2617d93713d9f4cf907ab2e7baef6a0f74f7198e
\ No newline at end of file
+34ffa3b3c002b0e87d8382ad76e87dbaec0b2bc6
\ No newline at end of file
diff --git a/src/expr.c b/src/expr.c
index c28f196221..817975ab3a 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1414,7 +1414,8 @@ int sqlite3ExprCanBeNull(const Expr *p){
       return 0;
     case TK_COLUMN:
       assert( p->pTab!=0 );
-      return p->iColumn>=0 && p->pTab->aCol[p->iColumn].notNull==0;
+      return ExprHasProperty(p, EP_CanBeNull) ||
+             (p->iColumn>=0 && p->pTab->aCol[p->iColumn].notNull==0);
     default:
       return 1;
   }
diff --git a/src/main.c b/src/main.c
index 2acc94edfd..47f96ac648 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1957,10 +1957,13 @@ int sqlite3_wal_checkpoint_v2(
   if( pnLog ) *pnLog = -1;
   if( pnCkpt ) *pnCkpt = -1;
 
-  assert( SQLITE_CHECKPOINT_FULL>SQLITE_CHECKPOINT_PASSIVE );
-  assert( SQLITE_CHECKPOINT_FULL<SQLITE_CHECKPOINT_RESTART );
-  assert( SQLITE_CHECKPOINT_PASSIVE+2==SQLITE_CHECKPOINT_RESTART );
-  if( eMode<SQLITE_CHECKPOINT_PASSIVE || eMode>SQLITE_CHECKPOINT_RESTART ){
+  assert( SQLITE_CHECKPOINT_PASSIVE==0 );
+  assert( SQLITE_CHECKPOINT_FULL==1 );
+  assert( SQLITE_CHECKPOINT_RESTART==2 );
+  assert( SQLITE_CHECKPOINT_TRUNCATE==3 );
+  if( eMode<SQLITE_CHECKPOINT_PASSIVE || eMode>SQLITE_CHECKPOINT_TRUNCATE ){
+    /* EVIDENCE-OF: R-03996-12088 The M parameter must be a valid checkpoint
+    ** mode: */
     return SQLITE_MISUSE;
   }
 
@@ -1988,7 +1991,9 @@ int sqlite3_wal_checkpoint_v2(
 ** checkpointed.
 */
 int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb){
-  return sqlite3_wal_checkpoint_v2(db, zDb, SQLITE_CHECKPOINT_PASSIVE, 0, 0);
+  /* EVIDENCE-OF: R-41613-20553 The sqlite3_wal_checkpoint(D,X) is equivalent to
+  ** sqlite3_wal_checkpoint_v2(D,X,SQLITE_CHECKPOINT_PASSIVE,0,0). */
+  return sqlite3_wal_checkpoint_v2(db,zDb,SQLITE_CHECKPOINT_PASSIVE,0,0);
 }
 
 #ifndef SQLITE_OMIT_WAL
diff --git a/src/pager.c b/src/pager.c
index e0ede87f07..a2ae9cc410 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -7075,7 +7075,8 @@ int sqlite3PagerCheckpoint(Pager *pPager, int eMode, int *pnLog, int *pnCkpt){
   int rc = SQLITE_OK;
   if( pPager->pWal ){
     rc = sqlite3WalCheckpoint(pPager->pWal, eMode,
-        pPager->xBusyHandler, pPager->pBusyHandlerArg,
+        (eMode==SQLITE_CHECKPOINT_PASSIVE ? 0 : pPager->xBusyHandler),
+        pPager->pBusyHandlerArg,
         pPager->ckptSyncFlags, pPager->pageSize, (u8 *)pPager->pTmpSpace,
         pnLog, pnCkpt
     );
diff --git a/src/pragma.c b/src/pragma.c
index 543f265ba9..ab9a283629 100644
--- a/src/pragma.c
+++ b/src/pragma.c
@@ -2195,7 +2195,7 @@ void sqlite3Pragma(
 
 #ifndef SQLITE_OMIT_WAL
   /*
-  **   PRAGMA [database.]wal_checkpoint = passive|full|restart
+  **   PRAGMA [database.]wal_checkpoint = passive|full|restart|truncate
   **
   ** Checkpoint the database.
   */
@@ -2207,6 +2207,8 @@ void sqlite3Pragma(
         eMode = SQLITE_CHECKPOINT_FULL;
       }else if( sqlite3StrICmp(zRight, "restart")==0 ){
         eMode = SQLITE_CHECKPOINT_RESTART;
+      }else if( sqlite3StrICmp(zRight, "truncate")==0 ){
+        eMode = SQLITE_CHECKPOINT_TRUNCATE;
       }
     }
     sqlite3VdbeSetNumCols(v, 3);
diff --git a/src/resolve.c b/src/resolve.c
index 8fb580b3a1..d4bd548c93 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -320,6 +320,10 @@ static int lookupName(
       if( pMatch ){
         pExpr->iTable = pMatch->iCursor;
         pExpr->pTab = pMatch->pTab;
+        assert( (pMatch->jointype & JT_RIGHT)==0 ); /* RIGHT JOIN not (yet) supported */
+        if( (pMatch->jointype & JT_LEFT)!=0 ){
+          ExprSetProperty(pExpr, EP_CanBeNull);
+        }
         pSchema = pExpr->pTab->pSchema;
       }
     } /* if( pSrcList ) */
diff --git a/src/select.c b/src/select.c
index 3b422f1100..070ac00410 100644
--- a/src/select.c
+++ b/src/select.c
@@ -4829,7 +4829,7 @@ int sqlite3Select(
   **
   ** is transformed to:
   **
-  **     SELECT xyz FROM ... GROUP BY xyz
+  **     SELECT xyz FROM ... GROUP BY xyz ORDER BY xyz
   **
   ** The second form is preferred as a single index (or temp-table) may be 
   ** used for both the ORDER BY and DISTINCT processing. As originally 
@@ -4842,7 +4842,6 @@ int sqlite3Select(
     p->selFlags &= ~SF_Distinct;
     p->pGroupBy = sqlite3ExprListDup(db, p->pEList, 0);
     pGroupBy = p->pGroupBy;
-    sSort.pOrderBy = 0;
     /* Notice that even thought SF_Distinct has been cleared from p->selFlags,
     ** the sDistinct.isTnct is still set.  Hence, isTnct represents the
     ** original setting of the SF_Distinct flag, not the current setting */
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index db0601bdb0..afa4d89eb9 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -1216,7 +1216,7 @@ struct sqlite3_vfs {
 ** </ul>
 **
 ** When unlocking, the same SHARED or EXCLUSIVE flag must be supplied as
-** was given no the corresponding lock.  
+** was given on the corresponding lock.  
 **
 ** The xShmLock method can transition between unlocked and SHARED or
 ** between unlocked and EXCLUSIVE.  It cannot transition between SHARED
@@ -1519,8 +1519,8 @@ struct sqlite3_mem_methods {
 ** [[SQLITE_CONFIG_MEMSTATUS]] <dt>SQLITE_CONFIG_MEMSTATUS</dt>
 ** <dd> ^The SQLITE_CONFIG_MEMSTATUS option takes single argument of type int,
 ** interpreted as a boolean, which enables or disables the collection of
-** memory allocation statistics. ^(When memory allocation statistics are disabled, the 
-** following SQLite interfaces become non-operational:
+** memory allocation statistics. ^(When memory allocation statistics are
+** disabled, the following SQLite interfaces become non-operational:
 **   <ul>
 **   <li> [sqlite3_memory_used()]
 **   <li> [sqlite3_memory_highwater()]
@@ -1561,7 +1561,8 @@ struct sqlite3_mem_methods {
 ** This configuration should not be used if an application-define page
 ** cache implementation is loaded using the [SQLITE_CONFIG_PCACHE2]
 ** configuration option.
-** ^There are three arguments to SQLITE_CONFIG_PAGECACHE: A pointer to 8-byte aligned
+** ^There are three arguments to SQLITE_CONFIG_PAGECACHE: A pointer to
+** 8-byte aligned
 ** memory, the size of each page buffer (sz), and the number of pages (N).
 ** The sz argument should be the size of the largest database page
 ** (a power of two between 512 and 32768) plus some extra bytes for each
@@ -1581,7 +1582,8 @@ struct sqlite3_mem_methods {
 ** [[SQLITE_CONFIG_HEAP]] <dt>SQLITE_CONFIG_HEAP</dt>
 ** <dd> ^The SQLITE_CONFIG_HEAP option specifies a static memory buffer 
 ** that SQLite will use for all of its dynamic memory allocation needs
-** beyond those provided for by [SQLITE_CONFIG_SCRATCH] and [SQLITE_CONFIG_PAGECACHE].
+** beyond those provided for by [SQLITE_CONFIG_SCRATCH] and
+** [SQLITE_CONFIG_PAGECACHE].
 ** ^The SQLITE_CONFIG_HEAP option is only available if SQLite is compiled
 ** with either [SQLITE_ENABLE_MEMSYS3] or [SQLITE_ENABLE_MEMSYS5] and returns
 ** [SQLITE_ERROR] if invoked otherwise.
@@ -1601,9 +1603,9 @@ struct sqlite3_mem_methods {
 ** [[SQLITE_CONFIG_MUTEX]] <dt>SQLITE_CONFIG_MUTEX</dt>
 ** <dd> ^(The SQLITE_CONFIG_MUTEX option takes a single argument which is a
 ** pointer to an instance of the [sqlite3_mutex_methods] structure.
-** The argument specifies alternative low-level mutex routines to be used in place
-** the mutex routines built into SQLite.)^  ^SQLite makes a copy of the
-** content of the [sqlite3_mutex_methods] structure before the call to
+** The argument specifies alternative low-level mutex routines to be used
+** in place the mutex routines built into SQLite.)^  ^SQLite makes a copy of
+** the content of the [sqlite3_mutex_methods] structure before the call to
 ** [sqlite3_config()] returns. ^If SQLite is compiled with
 ** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
 ** the entire mutexing subsystem is omitted from the build and hence calls to
@@ -1641,8 +1643,8 @@ struct sqlite3_mem_methods {
 **
 ** [[SQLITE_CONFIG_GETPCACHE2]] <dt>SQLITE_CONFIG_GETPCACHE2</dt>
 ** <dd> ^(The SQLITE_CONFIG_GETPCACHE2 option takes a single argument which
-** is a pointer to an [sqlite3_pcache_methods2] object.  SQLite copies of the current
-** page cache implementation into that object.)^ </dd>
+** is a pointer to an [sqlite3_pcache_methods2] object.  SQLite copies of
+** the current page cache implementation into that object.)^ </dd>
 **
 ** [[SQLITE_CONFIG_LOG]] <dt>SQLITE_CONFIG_LOG</dt>
 ** <dd> The SQLITE_CONFIG_LOG option is used to configure the SQLite
@@ -1667,8 +1669,9 @@ struct sqlite3_mem_methods {
 ** [[SQLITE_CONFIG_URI]] <dt>SQLITE_CONFIG_URI
 ** <dd>^(The SQLITE_CONFIG_URI option takes a single argument of type int.
 ** If non-zero, then URI handling is globally enabled. If the parameter is zero,
-** then URI handling is globally disabled.)^ ^If URI handling is globally enabled,
-** all filenames passed to [sqlite3_open()], [sqlite3_open_v2()], [sqlite3_open16()] or
+** then URI handling is globally disabled.)^ ^If URI handling is globally
+** enabled, all filenames passed to [sqlite3_open()], [sqlite3_open_v2()],
+** [sqlite3_open16()] or
 ** specified as part of [ATTACH] commands are interpreted as URIs, regardless
 ** of whether or not the [SQLITE_OPEN_URI] flag is set when the database
 ** connection is opened. ^If it is globally disabled, filenames are
@@ -1730,8 +1733,8 @@ struct sqlite3_mem_methods {
 ** [[SQLITE_CONFIG_WIN32_HEAPSIZE]]
 ** <dt>SQLITE_CONFIG_WIN32_HEAPSIZE
 ** <dd>^The SQLITE_CONFIG_WIN32_HEAPSIZE option is only available if SQLite is
-** compiled for Windows with the [SQLITE_WIN32_MALLOC] pre-processor macro defined.
-** ^SQLITE_CONFIG_WIN32_HEAPSIZE takes a 32-bit unsigned integer value
+** compiled for Windows with the [SQLITE_WIN32_MALLOC] pre-processor macro
+** defined. ^SQLITE_CONFIG_WIN32_HEAPSIZE takes a 32-bit unsigned integer value
 ** that specifies the maximum size of the created heap.
 ** </dl>
 **
@@ -1739,8 +1742,8 @@ struct sqlite3_mem_methods {
 ** <dt>SQLITE_CONFIG_PCACHE_HDRSZ
 ** <dd>^The SQLITE_CONFIG_PCACHE_HDRSZ option takes a single parameter which
 ** is a pointer to an integer and writes into that integer the number of extra
-** bytes per page required for each page in [SQLITE_CONFIG_PAGECACHE]. The amount of
-** extra space required can change depending on the compiler,
+** bytes per page required for each page in [SQLITE_CONFIG_PAGECACHE].
+** The amount of extra space required can change depending on the compiler,
 ** target platform, and SQLite version.
 ** </dl>
 */
@@ -2044,6 +2047,7 @@ int sqlite3_complete16(const void *sql);
 
 /*
 ** CAPI3REF: Register A Callback To Handle SQLITE_BUSY Errors
+** KEYWORDS: {busy-handler callback} {busy handler}
 **
 ** ^The sqlite3_busy_handler(D,X,P) routine sets a callback function X
 ** that might be invoked with argument P whenever
@@ -2060,7 +2064,7 @@ int sqlite3_complete16(const void *sql);
 ** ^The first argument to the busy handler is a copy of the void* pointer which
 ** is the third argument to sqlite3_busy_handler().  ^The second argument to
 ** the busy handler callback is the number of times that the busy handler has
-** been invoked for the same locking event.  ^If the
+** been invoked previously for the same locking event.  ^If the
 ** busy callback returns 0, then no additional attempts are made to
 ** access the database and [SQLITE_BUSY] is returned
 ** to the application.
@@ -4515,7 +4519,8 @@ typedef void (*sqlite3_destructor_type)(void*);
 ** the [sqlite3_context] pointer, the results are undefined.
 */
 void sqlite3_result_blob(sqlite3_context*, const void*, int, void(*)(void*));
-void sqlite3_result_blob64(sqlite3_context*,const void*,sqlite3_uint64,void(*)(void*));
+void sqlite3_result_blob64(sqlite3_context*,const void*,
+                           sqlite3_uint64,void(*)(void*));
 void sqlite3_result_double(sqlite3_context*, double);
 void sqlite3_result_error(sqlite3_context*, const char*, int);
 void sqlite3_result_error16(sqlite3_context*, const void*, int);
@@ -7241,97 +7246,114 @@ int sqlite3_wal_autocheckpoint(sqlite3 *db, int N);
 /*
 ** CAPI3REF: Checkpoint a database
 **
-** ^The [sqlite3_wal_checkpoint(D,X)] interface causes database named X
-** on [database connection] D to be [checkpointed].  ^If X is NULL or an
-** empty string, then a checkpoint is run on all databases of
-** connection D.  ^If the database connection D is not in
-** [WAL | write-ahead log mode] then this interface is a harmless no-op.
-** ^The [sqlite3_wal_checkpoint(D,X)] interface initiates a
-** [sqlite3_wal_checkpoint_v2|PASSIVE] checkpoint.
-** Use the [sqlite3_wal_checkpoint_v2()] interface to get a FULL
-** or RESET checkpoint.
+** ^(The sqlite3_wal_checkpoint(D,X) is equivalent to
+** [sqlite3_wal_checkpoint_v2](D,X,[SQLITE_CHECKPOINT_PASSIVE],0,0).)^
 **
-** ^The [wal_checkpoint pragma] can be used to invoke this interface
-** from SQL.  ^The [sqlite3_wal_autocheckpoint()] interface and the
-** [wal_autocheckpoint pragma] can be used to cause this interface to be
-** run whenever the WAL reaches a certain size threshold.
+** In brief, sqlite3_wal_checkpoint(D,X) causes the content in the 
+** [write-ahead log] for database X on [database connection] D to be
+** transferred into the database file and for the write-ahead log to
+** be reset.  See the [checkpointing] documentation for addition
+** information.
 **
-** See also: [sqlite3_wal_checkpoint_v2()]
+** This interface used to be the only way to cause a checkpoint to
+** occur.  But then the newer and more powerful [sqlite3_wal_checkpoint_v2()]
+** interface was added.  This interface is retained for backwards
+** compatibility and as a convenience for applications that need to manually
+** start a callback but which do not need the full power (and corresponding
+** complication) of [sqlite3_wal_checkpoint_v2()].
 */
 int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);
 
 /*
 ** CAPI3REF: Checkpoint a database
 **
-** Run a checkpoint operation on WAL database zDb attached to database 
-** handle db. The specific operation is determined by the value of the 
-** eMode parameter:
+** ^(The sqlite3_wal_checkpoint_v2(D,X,M,L,C) interface runs a checkpoint
+** operation on database X of [database connection] D in mode M.  Status
+** information is written back into integers pointed to by L and C.)^
+** ^(The M parameter must be a valid [checkpoint mode]:)^
 **
 ** <dl>
 ** <dt>SQLITE_CHECKPOINT_PASSIVE<dd>
-**   Checkpoint as many frames as possible without waiting for any database 
-**   readers or writers to finish. Sync the db file if all frames in the log
-**   are checkpointed. This mode is the same as calling 
-**   sqlite3_wal_checkpoint(). The [sqlite3_busy_handler|busy-handler callback]
-**   is never invoked.
+**   ^Checkpoint as many frames as possible without waiting for any database 
+**   readers or writers to finish, then sync the database file if all frames 
+**   in the log were checkpointed. ^The [busy-handler callback]
+**   is never invoked in the SQLITE_CHECKPOINT_PASSIVE mode.  
+**   ^On the other hand, passive mode might leave the checkpoint unfinished
+**   if there are concurrent readers or writers.
 **
 ** <dt>SQLITE_CHECKPOINT_FULL<dd>
-**   This mode blocks (it invokes the
+**   ^This mode blocks (it invokes the
 **   [sqlite3_busy_handler|busy-handler callback]) until there is no
 **   database writer and all readers are reading from the most recent database
-**   snapshot. It then checkpoints all frames in the log file and syncs the
-**   database file. This call blocks database writers while it is running,
-**   but not database readers.
+**   snapshot. ^It then checkpoints all frames in the log file and syncs the
+**   database file. ^This mode blocks new database writers while it is pending,
+**   but new database readers are allowed to continue unimpeded.
 **
 ** <dt>SQLITE_CHECKPOINT_RESTART<dd>
-**   This mode works the same way as SQLITE_CHECKPOINT_FULL, except after 
-**   checkpointing the log file it blocks (calls the 
-**   [sqlite3_busy_handler|busy-handler callback])
-**   until all readers are reading from the database file only. This ensures 
-**   that the next client to write to the database file restarts the log file 
-**   from the beginning. This call blocks database writers while it is running,
-**   but not database readers.
+**   ^This mode works the same way as SQLITE_CHECKPOINT_FULL with the addition
+**   that after checkpointing the log file it blocks (calls the 
+**   [busy-handler callback])
+**   until all readers are reading from the database file only. ^This ensures 
+**   that the next writer will restart the log file from the beginning.
+**   ^Like SQLITE_CHECKPOINT_FULL, this mode blocks new
+**   database writer attempts while it is pending, but does not impede readers.
+**
+** <dt>SQLITE_CHECKPOINT_TRUNCATE<dd>
+**   ^This mode works the same way as SQLITE_CHECKPOINT_RESTART with the
+**   addition that it also truncates the log file to zero bytes just prior
+**   to a successful return.
 ** </dl>
 **
-** If pnLog is not NULL, then *pnLog is set to the total number of frames in
-** the log file before returning. If pnCkpt is not NULL, then *pnCkpt is set to
-** the total number of checkpointed frames (including any that were already
-** checkpointed when this function is called). *pnLog and *pnCkpt may be
-** populated even if sqlite3_wal_checkpoint_v2() returns other than SQLITE_OK.
-** If no values are available because of an error, they are both set to -1
-** before returning to communicate this to the caller.
+** ^If pnLog is not NULL, then *pnLog is set to the total number of frames in
+** the log file or to -1 if the checkpoint could not run because
+** of an error or because the database is not in [WAL mode]. ^If pnCkpt is not
+** NULL,then *pnCkpt is set to the total number of checkpointed frames in the
+** log file (including any that were already checkpointed before the function
+** was called) or to -1 if the checkpoint could not run due to an error or
+** because the database is not in WAL mode. ^Note that upon successful
+** completion of an SQLITE_CHECKPOINT_TRUNCATE, the log file will have been
+** truncated to zero bytes and so both *pnLog and *pnCkpt will be set to zero.
 **
-** All calls obtain an exclusive "checkpoint" lock on the database file. If
+** ^All calls obtain an exclusive "checkpoint" lock on the database file. ^If
 ** any other process is running a checkpoint operation at the same time, the 
-** lock cannot be obtained and SQLITE_BUSY is returned. Even if there is a 
+** lock cannot be obtained and SQLITE_BUSY is returned. ^Even if there is a 
 ** busy-handler configured, it will not be invoked in this case.
 **
-** The SQLITE_CHECKPOINT_FULL and RESTART modes also obtain the exclusive 
-** "writer" lock on the database file. If the writer lock cannot be obtained
-** immediately, and a busy-handler is configured, it is invoked and the writer
-** lock retried until either the busy-handler returns 0 or the lock is
-** successfully obtained. The busy-handler is also invoked while waiting for
-** database readers as described above. If the busy-handler returns 0 before
+** ^The SQLITE_CHECKPOINT_FULL, RESTART and TRUNCATE modes also obtain the 
+** exclusive "writer" lock on the database file. ^If the writer lock cannot be
+** obtained immediately, and a busy-handler is configured, it is invoked and
+** the writer lock retried until either the busy-handler returns 0 or the lock
+** is successfully obtained. ^The busy-handler is also invoked while waiting for
+** database readers as described above. ^If the busy-handler returns 0 before
 ** the writer lock is obtained or while waiting for database readers, the
 ** checkpoint operation proceeds from that point in the same way as 
 ** SQLITE_CHECKPOINT_PASSIVE - checkpointing as many frames as possible 
-** without blocking any further. SQLITE_BUSY is returned in this case.
+** without blocking any further. ^SQLITE_BUSY is returned in this case.
 **
-** If parameter zDb is NULL or points to a zero length string, then the
-** specified operation is attempted on all WAL databases. In this case the
-** values written to output parameters *pnLog and *pnCkpt are undefined. If 
+** ^If parameter zDb is NULL or points to a zero length string, then the
+** specified operation is attempted on all WAL databases [attached] to 
+** [database connection] db.  In this case the
+** values written to output parameters *pnLog and *pnCkpt are undefined. ^If 
 ** an SQLITE_BUSY error is encountered when processing one or more of the 
 ** attached WAL databases, the operation is still attempted on any remaining 
-** attached databases and SQLITE_BUSY is returned to the caller. If any other 
+** attached databases and SQLITE_BUSY is returned at the end. ^If any other 
 ** error occurs while processing an attached database, processing is abandoned 
-** and the error code returned to the caller immediately. If no error 
+** and the error code is returned to the caller immediately. ^If no error 
 ** (SQLITE_BUSY or otherwise) is encountered while processing the attached 
 ** databases, SQLITE_OK is returned.
 **
-** If database zDb is the name of an attached database that is not in WAL
-** mode, SQLITE_OK is returned and both *pnLog and *pnCkpt set to -1. If
+** ^If database zDb is the name of an attached database that is not in WAL
+** mode, SQLITE_OK is returned and both *pnLog and *pnCkpt set to -1. ^If
 ** zDb is not NULL (or a zero length string) and is not the name of any
 ** attached database, SQLITE_ERROR is returned to the caller.
+**
+** ^Unless it returns SQLITE_MISUSE,
+** the sqlite3_wal_checkpoint_v2() interface
+** sets the error information that is queried by
+** [sqlite3_errcode()] and [sqlite3_errmsg()].
+**
+** ^The [PRAGMA wal_checkpoint] command can be used to invoke this interface
+** from SQL.
 */
 int sqlite3_wal_checkpoint_v2(
   sqlite3 *db,                    /* Database handle */
@@ -7342,16 +7364,18 @@ int sqlite3_wal_checkpoint_v2(
 );
 
 /*
-** CAPI3REF: Checkpoint operation parameters
+** CAPI3REF: Checkpoint Mode Values
+** KEYWORDS: {checkpoint mode}
 **
-** These constants can be used as the 3rd parameter to
-** [sqlite3_wal_checkpoint_v2()].  See the [sqlite3_wal_checkpoint_v2()]
-** documentation for additional information about the meaning and use of
-** each of these values.
+** These constants define all valid values for the "checkpoint mode" passed
+** as the third parameter to the [sqlite3_wal_checkpoint_v2()] interface.
+** See the [sqlite3_wal_checkpoint_v2()] documentation for details on the
+** meaning of each of these checkpoint modes.
 */
-#define SQLITE_CHECKPOINT_PASSIVE 0
-#define SQLITE_CHECKPOINT_FULL    1
-#define SQLITE_CHECKPOINT_RESTART 2
+#define SQLITE_CHECKPOINT_PASSIVE  0  /* Do as much as possible w/o blocking */
+#define SQLITE_CHECKPOINT_FULL     1  /* Wait for writers, then checkpoint */
+#define SQLITE_CHECKPOINT_RESTART  2  /* Like FULL but wait for for readers */
+#define SQLITE_CHECKPOINT_TRUNCATE 3  /* Like RESTART but also truncate WAL */
 
 /*
 ** CAPI3REF: Virtual Table Interface Configuration
@@ -7450,12 +7474,12 @@ int sqlite3_vtab_on_conflict(sqlite3 *);
 **
 ** <dl>
 ** [[SQLITE_SCANSTAT_NLOOP]] <dt>SQLITE_SCANSTAT_NLOOP</dt>
-** <dd>^The [sqlite3_int64] variable pointed to by the T parameter will be set to the
-** total number of times that the X-th loop has run.</dd>
+** <dd>^The [sqlite3_int64] variable pointed to by the T parameter will be
+** set to the total number of times that the X-th loop has run.</dd>
 **
 ** [[SQLITE_SCANSTAT_NVISIT]] <dt>SQLITE_SCANSTAT_NVISIT</dt>
-** <dd>^The [sqlite3_int64] variable pointed to by the T parameter will be set to the
-** total number of rows examined by all iterations of the X-th loop.</dd>
+** <dd>^The [sqlite3_int64] variable pointed to by the T parameter will be set
+** to the total number of rows examined by all iterations of the X-th loop.</dd>
 **
 ** [[SQLITE_SCANSTAT_EST]] <dt>SQLITE_SCANSTAT_EST</dt>
 ** <dd>^The "double" variable pointed to by the T parameter will be set to the
@@ -7466,14 +7490,14 @@ int sqlite3_vtab_on_conflict(sqlite3 *);
 ** be the NLOOP value for the current loop.
 **
 ** [[SQLITE_SCANSTAT_NAME]] <dt>SQLITE_SCANSTAT_NAME</dt>
-** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
-** a zero-terminated UTF-8 string containing the name of the index or table used
-** for the X-th loop.
+** <dd>^The "const char *" variable pointed to by the T parameter will be set
+** to a zero-terminated UTF-8 string containing the name of the index or table
+** used for the X-th loop.
 **
 ** [[SQLITE_SCANSTAT_EXPLAIN]] <dt>SQLITE_SCANSTAT_EXPLAIN</dt>
-** <dd>^The "const char *" variable pointed to by the T parameter will be set to 
-** a zero-terminated UTF-8 string containing the [EXPLAIN QUERY PLAN] description
-** for the X-th loop.
+** <dd>^The "const char *" variable pointed to by the T parameter will be set
+** to a zero-terminated UTF-8 string containing the [EXPLAIN QUERY PLAN]
+** description for the X-th loop.
 **
 ** [[SQLITE_SCANSTAT_SELECTID]] <dt>SQLITE_SCANSTAT_SELECT</dt>
 ** <dd>^The "int" variable pointed to by the T parameter will be set to the
@@ -7496,8 +7520,8 @@ int sqlite3_vtab_on_conflict(sqlite3 *);
 ** Return status data for a single loop within query pStmt.
 **
 ** The "iScanStatusOp" parameter determines which status information to return.
-** The "iScanStatusOp" must be one of the [scanstatus options] or the behavior of
-** this interface is undefined.
+** The "iScanStatusOp" must be one of the [scanstatus options] or the behavior
+** of this interface is undefined.
 ** ^The requested measurement is written into a variable pointed to by
 ** the "pOut" parameter.
 ** Parameter "idx" identifies the specific loop to retrieve statistics for.
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 8824e3129d..2b300f8e35 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -2023,7 +2023,7 @@ struct Expr {
 /*
 ** The following are the meanings of bits in the Expr.flags field.
 */
-#define EP_FromJoin  0x000001 /* Originated in ON or USING clause of a join */
+#define EP_FromJoin  0x000001 /* Originates in ON/USING clause of outer join */
 #define EP_Agg       0x000002 /* Contains one or more aggregate functions */
 #define EP_Resolved  0x000004 /* IDs have been resolved to COLUMNs */
 #define EP_Error     0x000008 /* Expression contains one or more errors */
@@ -2043,6 +2043,7 @@ struct Expr {
 #define EP_NoReduce  0x020000 /* Cannot EXPRDUP_REDUCE this Expr */
 #define EP_Unlikely  0x040000 /* unlikely() or likelihood() function */
 #define EP_Constant  0x080000 /* Node is a constant */
+#define EP_CanBeNull 0x100000 /* Can be null despite NOT NULL constraint */
 
 /*
 ** These macros can be used to test, set, or clear bits in the 
diff --git a/src/test1.c b/src/test1.c
index 1c43861547..be4ad92c11 100644
--- a/src/test1.c
+++ b/src/test1.c
@@ -5690,10 +5690,11 @@ static int test_wal_checkpoint_v2(
   int nCkpt = -555;
   Tcl_Obj *pRet;
 
-  const char * aMode[] = { "passive", "full", "restart", 0 };
+  const char * aMode[] = { "passive", "full", "restart", "truncate", 0 };
   assert( SQLITE_CHECKPOINT_PASSIVE==0 );
   assert( SQLITE_CHECKPOINT_FULL==1 );
   assert( SQLITE_CHECKPOINT_RESTART==2 );
+  assert( SQLITE_CHECKPOINT_TRUNCATE==3 );
 
   if( objc!=3 && objc!=4 ){
     Tcl_WrongNumArgs(interp, 1, objv, "DB MODE ?NAME?");
diff --git a/src/vdbe.c b/src/vdbe.c
index 890e41e1e9..48b080ecf9 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -5765,8 +5765,8 @@ case OP_AggFinal: {
 /* Opcode: Checkpoint P1 P2 P3 * *
 **
 ** Checkpoint database P1. This is a no-op if P1 is not currently in
-** WAL mode. Parameter P2 is one of SQLITE_CHECKPOINT_PASSIVE, FULL
-** or RESTART.  Write 1 or 0 into mem[P3] if the checkpoint returns
+** WAL mode. Parameter P2 is one of SQLITE_CHECKPOINT_PASSIVE, FULL,
+** RESTART, or TRUNCATE.  Write 1 or 0 into mem[P3] if the checkpoint returns
 ** SQLITE_BUSY or not, respectively.  Write the number of pages in the
 ** WAL after the checkpoint into mem[P3+1] and the number of pages
 ** in the WAL that have been checkpointed after the checkpoint
@@ -5784,6 +5784,7 @@ case OP_Checkpoint: {
   assert( pOp->p2==SQLITE_CHECKPOINT_PASSIVE
        || pOp->p2==SQLITE_CHECKPOINT_FULL
        || pOp->p2==SQLITE_CHECKPOINT_RESTART
+       || pOp->p2==SQLITE_CHECKPOINT_TRUNCATE
   );
   rc = sqlite3Checkpoint(db, pOp->p1, pOp->p2, &aRes[1], &aRes[2]);
   if( rc==SQLITE_BUSY ){
diff --git a/src/wal.c b/src/wal.c
index 3033444b41..2b80c7a95e 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -1623,6 +1623,38 @@ static int walPagesize(Wal *pWal){
   return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
 }
 
+/*
+** The following is guaranteed when this function is called:
+**
+**   a) the WRITER lock is held,
+**   b) the entire log file has been checkpointed, and
+**   c) any existing readers are reading exclusively from the database
+**      file - there are no readers that may attempt to read a frame from
+**      the log file.
+**
+** This function updates the shared-memory structures so that the next
+** client to write to the database (which may be this one) does so by
+** writing frames into the start of the log file.
+**
+** The value of parameter salt1 is used as the aSalt[1] value in the 
+** new wal-index header. It should be passed a pseudo-random value (i.e. 
+** one obtained from sqlite3_randomness()).
+*/
+static void walRestartHdr(Wal *pWal, u32 salt1){
+  volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+  int i;                          /* Loop counter */
+  u32 *aSalt = pWal->hdr.aSalt;   /* Big-endian salt values */
+  pWal->nCkpt++;
+  pWal->hdr.mxFrame = 0;
+  sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
+  memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
+  walIndexWriteHdr(pWal);
+  pInfo->nBackfill = 0;
+  pInfo->aReadMark[1] = 0;
+  for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
+  assert( pInfo->aReadMark[0]==0 );
+}
+
 /*
 ** Copy as much content as we can from the WAL back into the database file
 ** in response to an sqlite3_wal_checkpoint() request or the equivalent.
@@ -1657,7 +1689,7 @@ static int walPagesize(Wal *pWal){
 static int walCheckpoint(
   Wal *pWal,                      /* Wal connection */
   int eMode,                      /* One of PASSIVE, FULL or RESTART */
-  int (*xBusyCall)(void*),        /* Function to call when busy */
+  int (*xBusy)(void*),            /* Function to call when busy */
   void *pBusyArg,                 /* Context argument for xBusyHandler */
   int sync_flags,                 /* Flags for OsSync() (or 0) */
   u8 *zBuf                        /* Temporary buffer to use */
@@ -1671,7 +1703,6 @@ static int walCheckpoint(
   u32 mxPage;                     /* Max database page to write */
   int i;                          /* Loop counter */
   volatile WalCkptInfo *pInfo;    /* The checkpoint status information */
-  int (*xBusy)(void*) = 0;        /* Function to call when waiting for locks */
 
   szPage = walPagesize(pWal);
   testcase( szPage<=32768 );
@@ -1686,7 +1717,9 @@ static int walCheckpoint(
   }
   assert( pIter );
 
-  if( eMode!=SQLITE_CHECKPOINT_PASSIVE ) xBusy = xBusyCall;
+  /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
+  ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
+  assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
 
   /* Compute in mxSafeFrame the index of the last frame of the WAL that is
   ** safe to write into the database.  Frames beyond mxSafeFrame might
@@ -1775,19 +1808,38 @@ static int walCheckpoint(
     rc = SQLITE_OK;
   }
 
-  /* If this is an SQLITE_CHECKPOINT_RESTART operation, and the entire wal
-  ** file has been copied into the database file, then block until all
-  ** readers have finished using the wal file. This ensures that the next
-  ** process to write to the database restarts the wal file.
+  /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
+  ** entire wal file has been copied into the database file, then block 
+  ** until all readers have finished using the wal file. This ensures that 
+  ** the next process to write to the database restarts the wal file.
   */
   if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
     assert( pWal->writeLock );
     if( pInfo->nBackfill<pWal->hdr.mxFrame ){
       rc = SQLITE_BUSY;
-    }else if( eMode==SQLITE_CHECKPOINT_RESTART ){
+    }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
+      u32 salt1;
+      sqlite3_randomness(4, &salt1);
       assert( mxSafeFrame==pWal->hdr.mxFrame );
       rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
       if( rc==SQLITE_OK ){
+        if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
+          /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
+          ** SQLITE_CHECKPOINT_RESTART with the addition that it also
+          ** truncates the log file to zero bytes just prior to a
+          ** successful return.
+          **
+          ** In theory, it might be safe to do this without updating the
+          ** wal-index header in shared memory, as all subsequent reader or
+          ** writer clients should see that the entire log file has been
+          ** checkpointed and behave accordingly. This seems unsafe though,
+          ** as it would leave the system in a state where the contents of
+          ** the wal-index header do not match the contents of the 
+          ** file-system. To avoid this, update the wal-index header to
+          ** indicate that the log file contains zero valid frames.  */
+          walRestartHdr(pWal, salt1);
+          rc = sqlite3OsTruncate(pWal->pWalFd, 0);
+        }
         walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
       }
     }
@@ -2573,7 +2625,6 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
   return rc;
 }
 
-
 /*
 ** This function is called just before writing a set of frames to the log
 ** file (see sqlite3WalFrames()). It checks to see if, instead of appending
@@ -2606,20 +2657,8 @@ static int walRestartLog(Wal *pWal){
         ** In theory it would be Ok to update the cache of the header only
         ** at this point. But updating the actual wal-index header is also
         ** safe and means there is no special case for sqlite3WalUndo()
-        ** to handle if this transaction is rolled back.
-        */
-        int i;                    /* Loop counter */
-        u32 *aSalt = pWal->hdr.aSalt;       /* Big-endian salt values */
-
-        pWal->nCkpt++;
-        pWal->hdr.mxFrame = 0;
-        sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
-        aSalt[1] = salt1;
-        walIndexWriteHdr(pWal);
-        pInfo->nBackfill = 0;
-        pInfo->aReadMark[1] = 0;
-        for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
-        assert( pInfo->aReadMark[0]==0 );
+        ** to handle if this transaction is rolled back.  */
+        walRestartHdr(pWal, salt1);
         walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
       }else if( rc!=SQLITE_BUSY ){
         return rc;
@@ -2907,7 +2946,7 @@ int sqlite3WalFrames(
 */
 int sqlite3WalCheckpoint(
   Wal *pWal,                      /* Wal connection */
-  int eMode,                      /* PASSIVE, FULL or RESTART */
+  int eMode,                      /* PASSIVE, FULL, RESTART, or TRUNCATE */
   int (*xBusy)(void*),            /* Function to call when busy */
   void *pBusyArg,                 /* Context argument for xBusyHandler */
   int sync_flags,                 /* Flags to sync db file with (or 0) */
@@ -2919,29 +2958,42 @@ int sqlite3WalCheckpoint(
   int rc;                         /* Return code */
   int isChanged = 0;              /* True if a new wal-index header is loaded */
   int eMode2 = eMode;             /* Mode to pass to walCheckpoint() */
+  int (*xBusy2)(void*) = xBusy;   /* Busy handler for eMode2 */
 
   assert( pWal->ckptLock==0 );
   assert( pWal->writeLock==0 );
 
+  /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
+  ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
+  assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
+
   if( pWal->readOnly ) return SQLITE_READONLY;
   WALTRACE(("WAL%p: checkpoint begins\n", pWal));
+
+  /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive 
+  ** "checkpoint" lock on the database file. */
   rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
   if( rc ){
-    /* Usually this is SQLITE_BUSY meaning that another thread or process
-    ** is already running a checkpoint, or maybe a recovery.  But it might
-    ** also be SQLITE_IOERR. */
+    /* EVIDENCE-OF: R-10421-19736 If any other process is running a
+    ** checkpoint operation at the same time, the lock cannot be obtained and
+    ** SQLITE_BUSY is returned.
+    ** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured,
+    ** it will not be invoked in this case.
+    */
+    testcase( rc==SQLITE_BUSY );
+    testcase( xBusy!=0 );
     return rc;
   }
   pWal->ckptLock = 1;
 
-  /* If this is a blocking-checkpoint, then obtain the write-lock as well
-  ** to prevent any writers from running while the checkpoint is underway.
-  ** This has to be done before the call to walIndexReadHdr() below.
+  /* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and
+  ** TRUNCATE modes also obtain the exclusive "writer" lock on the database
+  ** file.
   **
-  ** If the writer lock cannot be obtained, then a passive checkpoint is
-  ** run instead. Since the checkpointer is not holding the writer lock,
-  ** there is no point in blocking waiting for any readers. Assuming no 
-  ** other error occurs, this function will return SQLITE_BUSY to the caller.
+  ** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained
+  ** immediately, and a busy-handler is configured, it is invoked and the
+  ** writer lock retried until either the busy-handler returns 0 or the
+  ** lock is successfully obtained.
   */
   if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){
     rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_WRITE_LOCK, 1);
@@ -2949,6 +3001,7 @@ int sqlite3WalCheckpoint(
       pWal->writeLock = 1;
     }else if( rc==SQLITE_BUSY ){
       eMode2 = SQLITE_CHECKPOINT_PASSIVE;
+      xBusy2 = 0;
       rc = SQLITE_OK;
     }
   }
@@ -2966,7 +3019,7 @@ int sqlite3WalCheckpoint(
     if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
       rc = SQLITE_CORRUPT_BKPT;
     }else{
-      rc = walCheckpoint(pWal, eMode2, xBusy, pBusyArg, sync_flags, zBuf);
+      rc = walCheckpoint(pWal, eMode2, xBusy2, pBusyArg, sync_flags, zBuf);
     }
 
     /* If no error occurred, set the output variables. */
diff --git a/src/where.c b/src/where.c
index 277c8833e8..bda2a801ea 100644
--- a/src/where.c
+++ b/src/where.c
@@ -3591,10 +3591,9 @@ static Bitmask codeOneLoopStart(
         Expr *pExpr = pWC->a[iTerm].pExpr;
         if( &pWC->a[iTerm] == pTerm ) continue;
         if( ExprHasProperty(pExpr, EP_FromJoin) ) continue;
-        testcase( pWC->a[iTerm].wtFlags & TERM_ORINFO );
-        testcase( pWC->a[iTerm].wtFlags & TERM_VIRTUAL );
-        if( pWC->a[iTerm].wtFlags & (TERM_ORINFO|TERM_VIRTUAL) ) continue;
+        if( (pWC->a[iTerm].wtFlags & TERM_VIRTUAL)!=0 ) continue;
         if( (pWC->a[iTerm].eOperator & WO_ALL)==0 ) continue;
+        testcase( pWC->a[iTerm].wtFlags & TERM_ORINFO );
         pExpr = sqlite3ExprDup(db, pExpr, 0);
         pAndExpr = sqlite3ExprAnd(db, pAndExpr, pExpr);
       }
diff --git a/test/distinct.test b/test/distinct.test
index 78c2c1df36..2fb90dc3e3 100644
--- a/test/distinct.test
+++ b/test/distinct.test
@@ -222,4 +222,34 @@ do_execsql_test 4.1 {
   SELECT quote(x) FROM t2 ORDER BY 1;
 } {'xyzzy' X'0000000000'}
 
+#----------------------------------------------------------------------------
+# Ticket [c5ea805691bfc4204b1cb9e9aa0103bd48bc7d34] (2014-12-04)
+# Make sure that DISTINCT works together with ORDER BY and descending
+# indexes.
+#
+do_execsql_test 5.1 {
+  DROP TABLE IF EXISTS t1;
+  CREATE TABLE t1(x);
+  INSERT INTO t1(x) VALUES(3),(1),(5),(2),(6),(4),(5),(1),(3);
+  CREATE INDEX t1x ON t1(x DESC);
+  SELECT DISTINCT x FROM t1 ORDER BY x ASC;
+} {1 2 3 4 5 6}
+do_execsql_test 5.2 {
+  SELECT DISTINCT x FROM t1 ORDER BY x DESC;
+} {6 5 4 3 2 1}
+do_execsql_test 5.3 {
+  SELECT DISTINCT x FROM t1 ORDER BY x;
+} {1 2 3 4 5 6}
+do_execsql_test 5.4 {
+  DROP INDEX t1x;
+  CREATE INDEX t1x ON t1(x ASC);
+  SELECT DISTINCT x FROM t1 ORDER BY x ASC;
+} {1 2 3 4 5 6}
+do_execsql_test 5.5 {
+  SELECT DISTINCT x FROM t1 ORDER BY x DESC;
+} {6 5 4 3 2 1}
+do_execsql_test 5.6 {
+  SELECT DISTINCT x FROM t1 ORDER BY x;
+} {1 2 3 4 5 6}
+
 finish_test
diff --git a/test/join5.test b/test/join5.test
index 45d8a31596..b0b0df4f9d 100644
--- a/test/join5.test
+++ b/test/join5.test
@@ -106,5 +106,59 @@ do_test join5-2.12 {
   execsql {SELECT * FROM xy LEFT JOIN ab ON NULL WHERE NULL}
 } {}
 
+# Ticket https://www.sqlite.org/src/tktview/6f2222d550f5b0ee7ed37601
+# Incorrect output on a LEFT JOIN.
+#
+do_execsql_test join5-3.1 {
+  DROP TABLE IF EXISTS t1;
+  DROP TABLE IF EXISTS t2;
+  DROP TABLE IF EXISTS t3;
+  CREATE TABLE x1(a);
+  INSERT INTO x1 VALUES(1);
+  CREATE TABLE x2(b NOT NULL);
+  CREATE TABLE x3(c, d);
+  INSERT INTO x3 VALUES('a', NULL);
+  INSERT INTO x3 VALUES('b', NULL);
+  INSERT INTO x3 VALUES('c', NULL);
+  SELECT * FROM x1 LEFT JOIN x2 LEFT JOIN x3 ON x3.d = x2.b;
+} {1 {} {} {}}
+do_execsql_test join5-3.2 {
+  DROP TABLE IF EXISTS t1;
+  DROP TABLE IF EXISTS t2;
+  DROP TABLE IF EXISTS t3;
+  DROP TABLE IF EXISTS t4;
+  DROP TABLE IF EXISTS t5;
+  CREATE TABLE t1(x text NOT NULL, y text);
+  CREATE TABLE t2(u text NOT NULL, x text NOT NULL);
+  CREATE TABLE t3(w text NOT NULL, v text);
+  CREATE TABLE t4(w text NOT NULL, z text NOT NULL);
+  CREATE TABLE t5(z text NOT NULL, m text);
+  INSERT INTO t1 VALUES('f6d7661f-4efe-4c90-87b5-858e61cd178b',NULL);
+  INSERT INTO t1 VALUES('f6ea82c3-2cad-45ce-ae8f-3ddca4fb2f48',NULL);
+  INSERT INTO t1 VALUES('f6f47499-ecb4-474b-9a02-35be73c235e5',NULL);
+  INSERT INTO t1 VALUES('56f47499-ecb4-474b-9a02-35be73c235e5',NULL);
+  INSERT INTO t3 VALUES('007f2033-cb20-494c-b135-a1e4eb66130c',
+                        'f6d7661f-4efe-4c90-87b5-858e61cd178b');
+  SELECT *
+    FROM t3
+         INNER JOIN t1 ON t1.x= t3.v AND t1.y IS NULL
+         LEFT JOIN t4  ON t4.w = t3.w
+         LEFT JOIN t5  ON t5.z = t4.z
+         LEFT JOIN t2  ON t2.u = t5.m
+         LEFT JOIN t1 xyz ON xyz.y = t2.x;
+} {007f2033-cb20-494c-b135-a1e4eb66130c f6d7661f-4efe-4c90-87b5-858e61cd178b f6d7661f-4efe-4c90-87b5-858e61cd178b {} {} {} {} {} {} {} {} {}}
+do_execsql_test join5-3.3 {
+  DROP TABLE IF EXISTS x1;
+  DROP TABLE IF EXISTS x2;
+  DROP TABLE IF EXISTS x3;
+  CREATE TABLE x1(a);
+  INSERT INTO x1 VALUES(1);
+  CREATE TABLE x2(b NOT NULL);
+  CREATE TABLE x3(c, d);
+  INSERT INTO x3 VALUES('a', NULL);
+  INSERT INTO x3 VALUES('b', NULL);
+  INSERT INTO x3 VALUES('c', NULL);
+  SELECT * FROM x1 LEFT JOIN x2 JOIN x3 WHERE x3.d = x2.b;
+} {}
 
 finish_test
diff --git a/test/wal5.test b/test/wal5.test
index 68750f1479..09c7d76040 100644
--- a/test/wal5.test
+++ b/test/wal5.test
@@ -55,7 +55,8 @@ foreach {testprefix do_wal_checkpoint} {
         if {[lsearch {-mode -db} $key]<0} { error "unknown switch: $key" }
       }
 
-      if {$a(-mode)!="restart" && $a(-mode)!="full"} { set a(-mode) passive }
+      set vals {restart full truncate}
+      if {[lsearch -exact $vals $a(-mode)]<0} { set a(-mode) passive }
 
       set cmd [list sqlite3_wal_checkpoint_v2 $dbhandle $a(-mode)]
       if {[info exists a(-db)]} { lappend sql $a(-db) }
@@ -278,6 +279,11 @@ foreach {testprefix do_wal_checkpoint} {
     9   RESTART   2   {1 4 3}   2
     10  RESTART   3   {1 4 4}   3
 
+    11  TRUNCATE  -   {0 0 0}   3
+    12  TRUNCATE  1   {1 3 3}   1
+    13  TRUNCATE  2   {1 4 3}   2
+    14  TRUNCATE  3   {1 4 4}   3
+
   } {
     do_multiclient_test tn {
       setup_and_attach_aux
@@ -348,6 +354,41 @@ foreach {testprefix do_wal_checkpoint} {
 
     do_test 3.$tn.6 { code3 { do_wal_checkpoint db3 } } {0 0 0}
   }
+
+  # Test SQLITE_CHECKPOINT_TRUNCATE.
+  #
+  do_multiclient_test tn {
+
+    code1 $do_wal_checkpoint
+    code2 $do_wal_checkpoint
+    code3 $do_wal_checkpoint
+
+    do_test 3.$tn.1 {
+      sql1 {
+        PRAGMA page_size = 1024;
+        PRAGMA journal_mode = WAL;
+        PRAGMA synchronous = normal;
+        CREATE TABLE t1(x, y);
+        CREATE INDEX i1 ON t1(x, y);
+        INSERT INTO t1 VALUES(1, 2);
+        INSERT INTO t1 VALUES(3, 4);
+      }
+      file size test.db-wal
+    } [wal_file_size 8 1024]
+
+    do_test 3.$tn.2 { do_wal_checkpoint db -mode truncate } {0 0 0}
+    do_test 3.$tn.3 { file size test.db-wal } 0
+
+    do_test 3.$tn.4 {
+      sql2 { SELECT * FROM t1 }
+    } {1 2 3 4}
+
+    do_test 3.$tn.5 {
+      sql2 { INSERT INTO t1 VALUES('a', 'b') }
+      file size test.db-wal
+    } [wal_file_size 2 1024]
+
+  }
 }
 
 
diff --git a/test/whereJ.test b/test/whereJ.test
index 8431c3a4b0..48924d0fcf 100644
--- a/test/whereJ.test
+++ b/test/whereJ.test
@@ -640,4 +640,39 @@ do_execsql_test 4.2 {
 } {/.*SCAN TABLE cx.*SEARCH TABLE px.*SEARCH TABLE le.*/}
 
 
+# The following test is derived from a performance problem reported from
+# the field.  Notice the multiple indexes with the same initial tables,
+# and the unusual WHERE clause terms.
+#
+do_test 5.1 {
+  set res [db eval {
+    DROP TABLE IF EXISTS t1;
+    CREATE TABLE t1(a,b,c,d,e,f,g,h);
+    CREATE INDEX t1abc ON t1(a,b,c);
+    CREATE INDEX t1abe ON t1(a,b,e);
+    CREATE INDEX t1abf ON t1(a,b,f);
+    ANALYZE;
+    DROP TABLE IF EXISTS sqlite_stat4;
+    DROP TABLE IF EXISTS sqlite_stat3;
+    DELETE FROM sqlite_stat1;
+    INSERT INTO sqlite_stat1(tbl,idx,stat)
+      VALUES('t1','t1abc','2000000 8000 1600 800'),
+            ('t1','t1abe','2000000 8000 1600 150'),
+            ('t1','t1abf','2000000 8000 1600 150');
+    ANALYZE sqlite_master;
+  
+    EXPLAIN QUERY PLAN
+    SELECT * FROM t1
+     WHERE (a=1 OR a=2)
+       AND (b=3 OR b=4)
+       AND (d>=5 AND d<=5)
+       AND ((e>=7 AND e<=7) OR (f>=8 AND f<=8))
+       AND g>0;
+  }]
+} {~/ANY/}
+do_test 5.2 {set res} {/USING INDEX t1abe/}
+do_test 5.3 {set res} {/USING INDEX t1abf/}
+
+
+
 finish_test