diff --git a/ext/misc/spellfix.c b/ext/misc/spellfix.c
index eb5442ed2f..7d4f5e9870 100644
--- a/ext/misc/spellfix.c
+++ b/ext/misc/spellfix.c
@@ -2148,10 +2148,10 @@ static int spellfix1BestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
       pIdxInfo->aConstraintUsage[iDistTerm].argvIndex = idx++;
       pIdxInfo->aConstraintUsage[iDistTerm].omit = 1;
     }
-    pIdxInfo->estimatedCost = (double)10000;
+    pIdxInfo->estimatedCost = 1e5;
   }else{
     pIdxInfo->idxNum = 0;
-    pIdxInfo->estimatedCost = (double)10000000;
+    pIdxInfo->estimatedCost = 1e50;
   }
   return SQLITE_OK;
 }
diff --git a/manifest b/manifest
index d549fe0174..6a85c4db62 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Remove\sthe\sundocumented\ssqlite3_foreign_key_check()\sAPI\sand\sreplace\sit\swith\nsqlite3_db_status(db,\sSQLITE_DBSTATUS_DEFERRED_FKS,\s...).\s\sAdd\stest\scases\nfor\sthe\snew\sfunctionality.
-D 2013-07-11T13:49:59.348
+C Merge\srecent\strunk\schanges\s(such\sas\sthe\squery_only\sPRAGMA,\sthe\ndefer_foreign_keys\sPRAGMA,\sand\sthe\sSQLITE_DBSTATUS_DEFERRED_FKS\sparameter\nto\ssqlite3_db_status())\sinto\sthe\ssessions\sbranch.
+D 2013-07-11T15:31:57.120
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in aff38bc64c582dd147f18739532198372587b0f0
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -114,7 +114,7 @@ F ext/misc/nextchar.c 80ba262d23238efcfcb3d72d71aa4513098e26a6
 F ext/misc/percentile.c bcbee3c061b884eccb80e21651daaae8e1e43c63
 F ext/misc/regexp.c c25c65fe775f5d9801fb8573e36ebe73f2c0c2e0
 F ext/misc/rot13.c 1ac6f95f99b575907b9b09c81a349114cf9be45a
-F ext/misc/spellfix.c 6d7ce6105a4b7729f6c44ccdf1ab7e80d9707c02
+F ext/misc/spellfix.c 5e1d547e9a2aed13897fa91bac924333f62fd2d9
 F ext/misc/vtshim.c 5fb6be7fe37659a8cbd1e16982d74cceacbc4543
 F ext/misc/wholenumber.c 784b12543d60702ebdd47da936e278aa03076212
 F ext/rtree/README 6315c0d73ebf0ec40dedb5aa0e942bc8b54e3761
@@ -198,7 +198,7 @@ F src/journal.c b4124532212b6952f42eb2c12fa3c25701d8ba8d
 F src/legacy.c 0df0b1550b9cc1f58229644735e317ac89131f12
 F src/lempar.c cdf0a000315332fc9b50b62f3b5e22e080a0952b
 F src/loadext.c c48f7f3f170e502fe0cc20748e03c6e0b5a016c2
-F src/main.c 93407bb51024f962ed9cf1c3e525e63484ebbdb9
+F src/main.c e974ea9db6214a5f7cb4c1765b49d3aba1e3409f
 F src/malloc.c fe085aa851b666b7c375c1ff957643dc20a04bf6
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c 437c7c4af964895d4650f29881df63535caaa1fa
@@ -223,7 +223,7 @@ F src/parse.y 9acfcc83ddbf0cf82f0ed9582ccf0ad6c366ff37
 F src/pcache.c f8043b433a57aba85384a531e3937a804432a346
 F src/pcache.h a5e4f5d9f5d592051d91212c5949517971ae6222
 F src/pcache1.c d23d07716de96c7c0c2503ec5051a4384c3fb938
-F src/pragma.c c87581d93a7518cba656b7919e32ded5d331b76a
+F src/pragma.c 2790c5175bc3f95d2a0cf39283d144b9b012fec7
 F src/prepare.c 2306be166bbeddf454e18bf8b21dba8388d05328
 F src/printf.c 41c49dac366a3a411190001a8ab495fa8887974e
 F src/random.c cd4a67b3953b88019f8cd4ccd81394a8ddfaba50
@@ -234,7 +234,7 @@ F src/shell.c c8cd06e6b66250a3ea0149c4edec30de14f57b6f
 F src/sqlite.h.in 17c84f6a2296a33a16141f4cff4b176278f3d1cc
 F src/sqlite3.rc fea433eb0a59f4c9393c8e6d76a6e2596b1fe0c0
 F src/sqlite3ext.h 886f5a34de171002ad46fae8c36a7d8051c190fc
-F src/sqliteInt.h 62b11aa829ab51446a52dfea93f14b8e1e5d5862
+F src/sqliteInt.h b25c57bb70c098aa05548ecde1948f4106cba472
 F src/sqliteLimit.h 164b0e6749d31e0daa1a4589a169d31c0dec7b3d
 F src/status.c 7ac05a5c7017d0b9f0b4bcd701228b784f987158
 F src/table.c 2cd62736f845d82200acfa1287e33feb3c15d62e
@@ -290,7 +290,7 @@ F src/update.c 19daebf6a0a67af5524913e93498d08388792128
 F src/utf.c 8d819e2e5104a430fc2005f018db14347c95a38f
 F src/util.c f566b5138099a2df8533b190d0dcc74b7dfbe0c9
 F src/vacuum.c d9c5759f4c5a438bb43c2086f72c5d2edabc36c8
-F src/vdbe.c 26f19a439806efdd9fb93b1874a4a7029a885142
+F src/vdbe.c 4a9d00a91da42f6540203fc4e694235fd21347c9
 F src/vdbe.h 1223e2548e0970cf96f573ff6b99f804a36ad683
 F src/vdbeInt.h 11feb11eb49d8b312741011d30d91c9c50b59de0
 F src/vdbeapi.c bca51b6ea254af3a1bbfd2a58522f6d6db214334
@@ -729,8 +729,9 @@ F test/permutations.test 742b8005bb3c782797a20beccdbe213ef52531fb
 F test/pragma.test 5e7de6c32a5d764f09437d2025f07e4917b9e178
 F test/pragma2.test 3a55f82b954242c642f8342b17dffc8b47472947
 F test/printf.test ec9870c4dce8686a37818e0bf1aba6e6a1863552
-F test/progress.test 5b075c3c790c7b2a61419bc199db87aaf48b8301
+F test/progress.test 552dc1edc37333a8d3098b8c26a2b7f06f5799d7
 F test/ptrchng.test ef1aa72d6cf35a2bbd0869a649b744e9d84977fc
+F test/queryonly.test 5f653159e0f552f0552d43259890c1089391dcca
 F test/quick.test 1681febc928d686362d50057c642f77a02c62e57
 F test/quota-glob.test 32901e9eed6705d68ca3faee2a06b73b57cb3c26
 F test/quota.test b5b3eec55a059e0fe493c66c6e27bd2c07676cfd
@@ -1116,7 +1117,7 @@ F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
 F tool/wherecosttest.c f407dc4c79786982a475261866a161cd007947ae
 F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
-P 3a2ab74c85a40e0e7ef2d6aef6ec23837cb788e6
-R 4b05e08ec28ee8fbe45f517a6910194e
+P d39e65fe702a2e11477f2d996f77404f45763368 6557c407983b067449deb76bc4c5248de64e07dc
+R a7fbb947af42ffbd616de92443f86cbe
 U drh
-Z 8f1a9fcd771ae153ffef09cc214c7392
+Z a9673e579f51d102bcb297135146bef6
diff --git a/manifest.uuid b/manifest.uuid
index 89b033640c..8073d518de 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-d39e65fe702a2e11477f2d996f77404f45763368
\ No newline at end of file
+8dfc0b78c38e519b64a796243ff7c0aff688ff36
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index b25c43be3d..263921abad 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1300,7 +1300,7 @@ void sqlite3_progress_handler(
   sqlite3_mutex_enter(db->mutex);
   if( nOps>0 ){
     db->xProgress = xProgress;
-    db->nProgressOps = nOps;
+    db->nProgressOps = (unsigned)nOps;
     db->pProgressArg = pArg;
   }else{
     db->xProgress = 0;
diff --git a/src/pragma.c b/src/pragma.c
index fd0ebc727c..9bbbfa8aa1 100644
--- a/src/pragma.c
+++ b/src/pragma.c
@@ -177,6 +177,7 @@ static int flagPragma(Parse *pParse, const char *zLeft, const char *zRight){
     { "fullfsync",                SQLITE_FullFSync     },
     { "checkpoint_fullfsync",     SQLITE_CkptFullFSync },
     { "reverse_unordered_selects", SQLITE_ReverseOrder  },
+    { "query_only",               SQLITE_QueryOnly     },
 #ifndef SQLITE_OMIT_AUTOMATIC_INDEX
     { "automatic_index",          SQLITE_AutoIndex     },
 #endif
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index f989c3a30b..86d0804fa0 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -944,7 +944,7 @@ struct sqlite3 {
 #ifndef SQLITE_OMIT_PROGRESS_CALLBACK
   int (*xProgress)(void *);     /* The progress callback */
   void *pProgressArg;           /* Argument to the progress callback */
-  int nProgressOps;             /* Number of opcodes for progress callback */
+  unsigned nProgressOps;        /* Number of opcodes for progress callback */
 #endif
 #ifndef SQLITE_OMIT_VIRTUALTABLE
   int nVTrans;                  /* Allocated size of aVTrans */
@@ -1019,6 +1019,8 @@ struct sqlite3 {
 #define SQLITE_LoadExtension  0x00200000  /* Enable load_extension */
 #define SQLITE_EnableTrigger  0x00400000  /* True to enable triggers */
 #define SQLITE_DeferFKs       0x00800000  /* Defer all FK constraints */
+#define SQLITE_QueryOnly      0x01000000  /* Disable database changes */
+
 
 /*
 ** Bits of the sqlite3.dbOptFlags field that are used by the
diff --git a/src/vdbe.c b/src/vdbe.c
index b957212e34..c354d3e274 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -562,12 +562,11 @@ int sqlite3VdbeExec(
   sqlite3 *db = p->db;       /* The database */
   u8 resetSchemaOnFault = 0; /* Reset schema after an error if positive */
   u8 encoding = ENC(db);     /* The database encoding */
-#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
-  int checkProgress;         /* True if progress callbacks are enabled */
-  int nProgressOps = 0;      /* Opcodes executed since progress callback. */
-#endif
   int iCompare = 0;          /* Result of last OP_Compare operation */
   unsigned nVmStep = 0;      /* Number of virtual machine steps */
+#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
+  unsigned nProgressOps = 0; /* nVmStep at last progress callback. */
+#endif
   Mem *aMem = p->aMem;       /* Copy of p->aMem */
   Mem *pIn1 = 0;             /* 1st input operand */
   Mem *pIn2 = 0;             /* 2nd input operand */
@@ -596,9 +595,6 @@ int sqlite3VdbeExec(
   db->busyHandler.nBusy = 0;
   CHECK_FOR_INTERRUPT;
   sqlite3VdbeIOTraceSql(p);
-#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
-  checkProgress = db->xProgress!=0;
-#endif
 #ifdef SQLITE_DEBUG
   sqlite3BeginBenignMalloc();
   if( p->pc==0  && (p->db->flags & SQLITE_VdbeListing)!=0 ){
@@ -646,27 +642,6 @@ int sqlite3VdbeExec(
     }
 #endif
 
-#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
-    /* Call the progress callback if it is configured and the required number
-    ** of VDBE ops have been executed (either since this invocation of
-    ** sqlite3VdbeExec() or since last time the progress callback was called).
-    ** If the progress callback returns non-zero, exit the virtual machine with
-    ** a return code SQLITE_ABORT.
-    */
-    if( checkProgress ){
-      if( db->nProgressOps==nProgressOps ){
-        int prc;
-        prc = db->xProgress(db->pProgressArg);
-        if( prc!=0 ){
-          rc = SQLITE_INTERRUPT;
-          goto vdbe_error_halt;
-        }
-        nProgressOps = 0;
-      }
-      nProgressOps++;
-    }
-#endif
-
     /* On any opcode with the "out2-prerelease" tag, free any
     ** external allocations out of mem[p2] and set mem[p2] to be
     ** an undefined integer.  Opcodes will either fill in the integer
@@ -759,8 +734,38 @@ int sqlite3VdbeExec(
 ** the program.
 */
 case OP_Goto: {             /* jump */
-  CHECK_FOR_INTERRUPT;
   pc = pOp->p2 - 1;
+
+  /* Opcodes that are used as the bottom of a loop (OP_Next, OP_Prev,
+  ** OP_VNext, OP_RowSetNext, or OP_SorterNext) all jump here upon
+  ** completion.  Check to see if sqlite3_interrupt() has been called
+  ** or if the progress callback needs to be invoked. 
+  **
+  ** This code uses unstructured "goto" statements and does not look clean.
+  ** But that is not due to sloppy coding habits. The code is written this
+  ** way for performance, to avoid having to run the interrupt and progress
+  ** checks on every opcode.  This helps sqlite3_step() to run about 1.5%
+  ** faster according to "valgrind --tool=cachegrind" */
+check_for_interrupt:
+  CHECK_FOR_INTERRUPT;
+#ifndef SQLITE_OMIT_PROGRESS_CALLBACK
+  /* Call the progress callback if it is configured and the required number
+  ** of VDBE ops have been executed (either since this invocation of
+  ** sqlite3VdbeExec() or since last time the progress callback was called).
+  ** If the progress callback returns non-zero, exit the virtual machine with
+  ** a return code SQLITE_ABORT.
+  */
+  if( db->xProgress!=0 && (nVmStep - nProgressOps)>=db->nProgressOps ){
+    int prc;
+    prc = db->xProgress(db->pProgressArg);
+    if( prc!=0 ){
+      rc = SQLITE_INTERRUPT;
+      goto vdbe_error_halt;
+    }
+    nProgressOps = nVmStep;
+  }
+#endif
+  
   break;
 }
 
@@ -2953,6 +2958,10 @@ case OP_Transaction: {
   assert( p->readOnly==0 || pOp->p2==0 );
   assert( pOp->p1>=0 && pOp->p1<db->nDb );
   assert( (p->btreeMask & (((yDbMask)1)<<pOp->p1))!=0 );
+  if( pOp->p2 && (db->flags & SQLITE_QueryOnly)!=0 ){
+    rc = SQLITE_READONLY;
+    goto abort_due_to_error;
+  }
   pBt = db->aDb[pOp->p1].pBt;
 
   if( pBt ){
@@ -4557,7 +4566,6 @@ case OP_Next: {        /* jump */
   VdbeCursor *pC;
   int res;
 
-  CHECK_FOR_INTERRUPT;
   assert( pOp->p1>=0 && pOp->p1<p->nCursor );
   assert( pOp->p5<=ArraySize(p->aCounter) );
   pC = p->apCsr[pOp->p1];
@@ -4586,7 +4594,7 @@ case OP_Next: {        /* jump */
 #endif
   }
   pC->rowidIsValid = 0;
-  break;
+  goto check_for_interrupt;
 }
 
 /* Opcode: IdxInsert P1 P2 P3 * P5
@@ -5112,7 +5120,7 @@ case OP_RowSetAdd: {       /* in1, in2 */
 */
 case OP_RowSetRead: {       /* jump, in1, out3 */
   i64 val;
-  CHECK_FOR_INTERRUPT;
+
   pIn1 = &aMem[pOp->p1];
   if( (pIn1->flags & MEM_RowSet)==0 
    || sqlite3RowSetNext(pIn1->u.pRowSet, &val)==0
@@ -5124,7 +5132,7 @@ case OP_RowSetRead: {       /* jump, in1, out3 */
     /* A value was pulled from the index */
     sqlite3VdbeMemSetInt64(&aMem[pOp->p3], val);
   }
-  break;
+  goto check_for_interrupt;
 }
 
 /* Opcode: RowSetTest P1 P2 P3 P4
@@ -6027,7 +6035,7 @@ case OP_VNext: {   /* jump */
     /* If there is data, jump to P2 */
     pc = pOp->p2 - 1;
   }
-  break;
+  goto check_for_interrupt;
 }
 #endif /* SQLITE_OMIT_VIRTUALTABLE */
 
diff --git a/test/progress.test b/test/progress.test
index b25a100530..381f4826c8 100644
--- a/test/progress.test
+++ b/test/progress.test
@@ -166,7 +166,7 @@ do_test progress-1.7 {
   set ::res [list]
   db eval {SELECT a, b, c FROM abc} {
     lappend ::res $a $b $c
-    db progress 10 "expr 1"
+    db progress 5 "expr 1"
     catch {db eval {SELECT a, b, c FROM abc} { }} msg
     lappend ::res $msg
   }
diff --git a/test/queryonly.test b/test/queryonly.test
new file mode 100644
index 0000000000..2774e5d436
--- /dev/null
+++ b/test/queryonly.test
@@ -0,0 +1,72 @@
+# 2013-07-11
+#
+# 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.
+#
+# This file tests the "query_only" pragma.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+
+do_execsql_test queryonly-1.1 {
+  CREATE TABLE t1(a);
+  INSERT INTO t1 VALUES(123),(456);
+  SELECT a FROM t1 ORDER BY a;
+} {123 456}
+do_execsql_test queryonly-1.2 {
+  PRAGMA query_only;
+} {0}
+do_execsql_test queryonly-1.3 {
+  PRAGMA query_only=ON;
+  PRAGMA query_only;
+} {1}
+do_test queryonly-1.4 {
+  catchsql {INSERT INTO t1 VALUES(789);}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.5 {
+  catchsql {DELETE FROM t1;}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.6 {
+  catchsql {UPDATE t1 SET a=a+1;}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.7 {
+  catchsql {CREATE TABLE t2(b);}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.8 {
+  catchsql {CREATE INDEX t1a ON t1(a);}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.9 {
+  catchsql {DROP TABLE t1;}
+} {1 {attempt to write a readonly database}}
+do_test queryonly-1.10 {
+  catchsql {ANALYZE;}
+} {1 {attempt to write a readonly database}}
+do_execsql_test queryonly-1.11 {
+  SELECT a FROM t1 ORDER BY a;
+} {123 456}
+
+do_execsql_test queryonly-2.2 {
+  PRAGMA query_only;
+} {1}
+do_execsql_test queryonly-2.3 {
+  PRAGMA query_only=OFF;
+  PRAGMA query_only;
+} {0}
+do_execsql_test queryonly-2.4 {
+  INSERT INTO t1 VALUES(789);
+  SELECT a FROM t1 ORDER BY a;
+} {123 456 789}
+do_execsql_test queryonly-2.5 {
+  UPDATE t1 SET a=a+1;
+  SELECT a FROM t1 ORDER BY a;
+} {124 457 790}
+
+finish_test