Index: ext/rbu/rbu.c
==================================================================
--- ext/rbu/rbu.c
+++ ext/rbu/rbu.c
@@ -22,16 +22,26 @@
 /*
 ** Print a usage message and exit.
 */
 void usage(const char *zArgv0){
   fprintf(stderr, 
-"Usage: %s [-step NSTEP] TARGET-DB RBU-DB\n"
+"Usage: %s ?OPTIONS? TARGET-DB RBU-DB\n"
+"\n"
+"Where options are:\n"
+"\n"
+"    -step NSTEP\n"
+"    -vacuum\n"
+"\n"
+"  If the -vacuum switch is not present, argument RBU-DB must be an RBU\n"
+"  database containing an update suitable for target database TARGET-DB.\n"
+"  Or, if -vacuum is specified, then TARGET-DB is a database to vacuum using\n"
+"  RBU, and RBU-DB is used as the state database for the vacuum (refer to\n"
+"  API documentation for details).\n"
 "\n"
-"  Argument RBU-DB must be an RBU database containing an update suitable for\n"
-"  target database TARGET-DB. If NSTEP is set to less than or equal to zero\n"
-"  (the default value), this program attempts to apply the entire update to\n"
-"  the target database.\n"
+"  If NSTEP is set to less than or equal to zero (the default value), this \n"
+"  program attempts to perform the entire update or vacuum operation before\n"
+"  exiting\n"
 "\n"
 "  If NSTEP is greater than zero, then a maximum of NSTEP calls are made\n"
 "  to sqlite3rbu_step(). If the RBU update has not been completely applied\n"
 "  after the NSTEP'th call is made, the state is saved in the database RBU-DB\n"
 "  and the program exits. Subsequent invocations of this (or any other RBU)\n"
@@ -67,33 +77,47 @@
   const char *zRbu;               /* Database containing RBU */
   char zBuf[200];                 /* Buffer for printf() */
   char *zErrmsg;                  /* Error message, if any */
   sqlite3rbu *pRbu;               /* RBU handle */
   int nStep = 0;                  /* Maximum number of step() calls */
+  int bVacuum = 0;
   int rc;
   sqlite3_int64 nProgress = 0;
-
-  /* Process command line arguments. Following this block local variables 
-  ** zTarget, zRbu and nStep are all set. */
-  if( argc==5 ){
-    size_t nArg1 = strlen(argv[1]);
-    if( nArg1>5 || nArg1<2 || memcmp("-step", argv[1], nArg1) ) usage(argv[0]);
-    nStep = atoi(argv[2]);
-  }else if( argc!=3 ){
-    usage(argv[0]);
-  }
+  int nArg = argc-2;
+
+  if( argc<3 ) usage(argv[0]);
+  for(i=1; i<nArg; i++){
+    const char *zArg = argv[i];
+    int nArg = strlen(zArg);
+    if( nArg>1 && nArg<=8 && 0==memcmp(zArg, "-vacuum", nArg) ){
+      bVacuum = 1;
+    }else if( nArg>1 && nArg<=5 && 0==memcmp(zArg, "-step", nArg) && i<nArg-1 ){
+      i++;
+      nStep = atoi(argv[i]);
+    }else{
+      usage(argv[0]);
+    }
+  }
+
   zTarget = argv[argc-2];
   zRbu = argv[argc-1];
 
   report_default_vfs();
 
-  /* Open an RBU handle. If nStep is less than or equal to zero, call
+  /* Open an RBU handle. A vacuum handle if -vacuum was specified, or a
+  ** regular RBU update handle otherwise.  */
+  if( bVacuum ){
+    pRbu = sqlite3rbu_vacuum(zTarget, zRbu);
+  }else{
+    pRbu = sqlite3rbu_open(zTarget, zRbu, 0);
+  }
+  report_rbu_vfs(pRbu);
+
+  /* If nStep is less than or equal to zero, call
   ** sqlite3rbu_step() until either the RBU has been completely applied
   ** or an error occurs. Or, if nStep is greater than zero, call
   ** sqlite3rbu_step() a maximum of nStep times.  */
-  pRbu = sqlite3rbu_open(zTarget, zRbu, 0);
-  report_rbu_vfs(pRbu);
   for(i=0; (nStep<=0 || i<nStep) && sqlite3rbu_step(pRbu)==SQLITE_OK; i++);
   nProgress = sqlite3rbu_progress(pRbu);
   rc = sqlite3rbu_close(pRbu, &zErrmsg);
 
   /* Let the user know what happened. */

ADDED   ext/rbu/rbufault3.test
Index: ext/rbu/rbufault3.test
==================================================================
--- /dev/null
+++ ext/rbu/rbufault3.test
@@ -0,0 +1,98 @@
+# 2016 April 20
+#
+# 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 contains fault injection tests for RBU vacuum operations.
+#
+
+source [file join [file dirname [info script]] rbu_common.tcl]
+source $testdir/malloc_common.tcl
+set ::testprefix rbufault3
+
+foreach {fault errlist} {
+  oom-* {
+    {1 SQLITE_NOMEM}
+    {1 SQLITE_IOERR_NOMEM}
+    {1 {SQLITE_NOMEM - out of memory}}
+  }
+
+  ioerr-* {
+    {1 {SQLITE_IOERR - disk I/O error}}
+    {1 SQLITE_IOERR} 
+    {1 SQLITE_IOERR_WRITE} 
+    {1 SQLITE_IOERR_FSYNC} 
+    {1 SQLITE_IOERR_READ} 
+    {1 {SQLITE_IOERR - unable to open database: test.db2}} 
+    {1 {SQLITE_ERROR - unable to open database: test.db2}} 
+    {1 {SQLITE_ERROR - SQL logic error or missing database}}
+  }
+
+  cantopen* {
+    {1 {SQLITE_CANTOPEN - unable to open database: test.db2}}  
+    {1 {SQLITE_CANTOPEN - unable to open database: test.db2}}  
+    {1 {SQLITE_CANTOPEN - unable to open database file}}  
+    {1 SQLITE_CANTOPEN} 
+  }
+
+} {
+
+  reset_db
+  do_execsql_test 0 {
+    CREATE TABLE target(x UNIQUE, y, z, PRIMARY KEY(y));
+    INSERT INTO target VALUES(1, 2, 3);
+    INSERT INTO target VALUES(4, 5, 6);
+    INSERT INTO target VALUES(7, 8, 9);
+    CREATE INDEX i1 ON target(z);
+  }
+  faultsim_save_and_close
+
+  do_faultsim_test 1 -faults $fault -prep {
+    faultsim_restore_and_reopen
+    forcedelete test.db2
+  } -body {
+    sqlite3rbu_vacuum rbu test.db test.db2
+    while {[rbu step]=="SQLITE_OK"} {}
+    rbu close
+  } -test {
+    eval [list faultsim_test_result {0 SQLITE_DONE} {*}$::errlist]
+  }
+
+  do_faultsim_test 2 -faults $fault -prep {
+    faultsim_restore_and_reopen
+    forcedelete test.db2
+  } -body {
+    sqlite3rbu_vacuum rbu test.db test.db2
+    rbu step
+    rbu close
+  } -test {
+    eval [list faultsim_test_result {0 SQLITE_OK} {*}$::errlist]
+  }
+
+  forcedelete test.db2
+  sqlite3rbu_vacuum rbu test.db test.db2
+  rbu step
+  rbu close
+  faultsim_save_and_close
+
+  do_faultsim_test 3 -faults $fault -prep {
+    faultsim_restore_and_reopen
+    forcedelete test.db2
+  } -body {
+    sqlite3rbu_vacuum rbu test.db test.db2
+    rbu step
+    rbu close
+  } -test {
+    eval [list faultsim_test_result {0 SQLITE_OK} {*}$::errlist]
+  }
+
+}
+
+finish_test
+

ADDED   ext/rbu/rbuvacuum.test
Index: ext/rbu/rbuvacuum.test
==================================================================
--- /dev/null
+++ ext/rbu/rbuvacuum.test
@@ -0,0 +1,315 @@
+# 2016 April 15
+#
+# 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 contains tests for the RBU module. More specifically, it
+# contains tests to ensure that the sqlite3rbu_vacuum() API works as
+# expected.
+#
+
+source [file join [file dirname [info script]] rbu_common.tcl]
+set ::testprefix rbuvacuum
+
+proc do_rbu_vacuum_test {tn step} {
+  uplevel [list do_test $tn.1 {
+    if {$step==0} { sqlite3rbu_vacuum rbu test.db state.db }
+    while 1 {
+      if {$step==1} { sqlite3rbu_vacuum rbu test.db state.db }
+      set rc [rbu step]
+      if {$rc!="SQLITE_OK"} break
+      if {$step==1} { rbu close }
+    }
+    rbu close
+  } {SQLITE_DONE}]
+
+  uplevel [list do_execsql_test $tn.2 {
+    PRAGMA integrity_check
+  } ok]
+}
+
+foreach step {0 1} {
+
+  set ::testprefix rbuvacuum-step=$step
+  reset_db
+
+  # Simplest possible vacuum.
+  do_execsql_test 1.0 {
+    PRAGMA page_size = 1024;
+    CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
+    INSERT INTO t1 VALUES(1, 2, 3);
+    INSERT INTO t1 VALUES(4, 5, 6);
+    INSERT INTO t1 VALUES(7, 8, 9);
+    PRAGMA integrity_check;
+  } {ok}
+  do_rbu_vacuum_test 1.1 $step
+
+  # A vacuum that actually reclaims space.
+  do_execsql_test 1.2.1 {
+    INSERT INTO t1 VALUES(8, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(9, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(10, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(11, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(12, randomblob(900), randomblob(900));
+    PRAGMA page_count;
+  } {12}
+  do_execsql_test 1.2.2 {
+    DELETE FROM t1 WHERE rowid BETWEEN 8 AND 11;
+    PRAGMA page_count;
+  } {12}
+  do_rbu_vacuum_test 1.2.3 $step
+  do_execsql_test 1.2.4 {
+    PRAGMA page_count;
+  } {3}
+  
+  # Add an index to the table.
+  do_execsql_test 1.3.1 {
+    CREATE INDEX t1b ON t1(b);
+    INSERT INTO t1 VALUES(13, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(14, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(15, randomblob(900), randomblob(900));
+    INSERT INTO t1 VALUES(16, randomblob(900), randomblob(900));
+    PRAGMA page_count;
+  } {18}
+  do_execsql_test 1.3.2 {
+    DELETE FROM t1 WHERE rowid BETWEEN 12 AND 15;
+    PRAGMA page_count;
+  } {18}
+  do_rbu_vacuum_test 1.3.3 $step
+  do_execsql_test 1.3.4 {
+    PRAGMA page_count;
+  } {5}
+
+  # WITHOUT ROWID table.
+  do_execsql_test 1.4.1 {
+    CREATE TABLE t2(a, b, c, PRIMARY KEY(a, b)) WITHOUT ROWID;
+
+    INSERT INTO t2 VALUES(randomblob(900), 1, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 2, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 3, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 4, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 6, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 7, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 8, randomblob(900));
+
+    DELETE FROM t2 WHERE b BETWEEN 2 AND 7;
+    PRAGMA page_count;
+  } {20}
+  do_rbu_vacuum_test 1.4.2 $step
+  do_execsql_test 1.4.3 {
+    PRAGMA page_count;
+  } {10}
+  
+  # WITHOUT ROWID table with an index.
+  do_execsql_test 1.4.1 {
+    CREATE INDEX t2c ON t2(c);
+
+    INSERT INTO t2 VALUES(randomblob(900), 9, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 10, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 11, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 12, randomblob(900));
+    INSERT INTO t2 VALUES(randomblob(900), 13, randomblob(900));
+
+    DELETE FROM t2 WHERE b BETWEEN 8 AND 12;
+    PRAGMA page_count;
+  } {35}
+  do_rbu_vacuum_test 1.4.2 $step
+  do_execsql_test 1.4.3 {
+    PRAGMA page_count;
+  } {15}
+  do_execsql_test 1.4.4 {
+    VACUUM;
+    PRAGMA page_count;
+  } {15}
+
+  do_execsql_test 1.5.1 {
+    CREATE TABLE t3(a, b, c);
+    INSERT INTO t3 VALUES('a', 'b', 'c');
+    INSERT INTO t3 VALUES('d', 'e', 'f');
+    INSERT INTO t3 VALUES('g', 'h', 'i');
+  }
+  do_rbu_vacuum_test 1.5.2 $step
+  do_execsql_test 1.5.3 {
+    SELECT * FROM t3
+  } {a b c d e f g h i}
+  do_execsql_test 1.5.4 {
+    CREATE INDEX t3a ON t3(a);
+    CREATE INDEX t3b ON t3(b);
+    CREATE INDEX t3c ON t3(c);
+    INSERT INTO t3 VALUES('j', 'k', 'l');
+    DELETE FROM t3 WHERE a = 'g';
+  }
+  do_rbu_vacuum_test 1.5.5 $step
+  do_execsql_test 1.5.6 {
+    SELECT rowid, * FROM t3 ORDER BY b
+  } {1 a b c 2 d e f 4 j k l}
+
+  do_execsql_test 1.6.1 {
+    CREATE TABLE t4(a PRIMARY KEY, b, c);
+    INSERT INTO t4 VALUES('a', 'b', 'c');
+    INSERT INTO t4 VALUES('d', 'e', 'f');
+    INSERT INTO t4 VALUES('g', 'h', 'i');
+  }
+  do_rbu_vacuum_test 1.6.2 $step
+  do_execsql_test 1.6.3 {
+    SELECT * FROM t4
+  } {a b c d e f g h i}
+  do_execsql_test 1.6.4 {
+    CREATE INDEX t4a ON t4(a);
+    CREATE INDEX t4b ON t4(b);
+    CREATE INDEX t4c ON t4(c);
+    
+    INSERT INTO t4 VALUES('j', 'k', 'l');
+    DELETE FROM t4 WHERE a='g';
+  }
+  do_rbu_vacuum_test 1.6.5 $step
+  do_execsql_test 1.6.6 {
+    SELECT * FROM t4 ORDER BY b
+  } {a b c d e f j k l}
+
+  reset_db
+  do_execsql_test 1.7.0 {
+    CREATE TABLE t1(a INTEGER PRIMARY KEY AUTOINCREMENT, b);
+    INSERT INTO t1 VALUES(NULL, 'one');
+    INSERT INTO t1 VALUES(NULL, 'two');
+    DELETE FROM t1 WHERE a=2;
+    INSERT INTO t1 VALUES(NULL, 'three');
+    INSERT INTO t1 VALUES(NULL, 'four');
+    DELETE FROM t1 WHERE a=4;
+    INSERT INTO t1 VALUES(NULL, 'five');
+    INSERT INTO t1 VALUES(NULL, 'six');
+    DELETE FROM t1 WHERE a=6;
+    SELECT * FROM t1;
+  } {1 one 3 three 5 five}
+  do_rbu_vacuum_test 1.7.1 $step
+  do_execsql_test 1.7.2 {
+    INSERT INTO t1 VALUES(NULL, 'seven');
+    SELECT * FROM t1;
+  } {1 one 3 three 5 five 7 seven}
+
+  reset_db
+  do_execsql_test 1.8.0 {
+    CREATE TABLE t1(a INTEGER PRIMARY KEY AUTOINCREMENT, b);
+    CREATE INDEX i1 ON t1(b);
+    INSERT INTO t1 VALUES(NULL, 'one');
+    INSERT INTO t1 VALUES(NULL, 'two');
+    INSERT INTO t1 VALUES(NULL, 'three');
+    INSERT INTO t1 VALUES(NULL, 'four');
+    INSERT INTO t1 VALUES(NULL, 'five');
+    INSERT INTO t1 VALUES(NULL, 'six');
+    ANALYZE;
+    SELECT * FROM sqlite_stat1;
+  } {t1 i1 {6 1}}
+  do_rbu_vacuum_test 1.8.1 $step
+  do_execsql_test 1.7.2 {
+    SELECT * FROM sqlite_stat1;
+  } {t1 i1 {6 1}}
+
+  reset_db
+  do_execsql_test 1.9.0 {
+    PRAGMA page_size = 8192;
+    PRAGMA auto_vacuum = 2;
+    PRAGMA user_version = 412;
+    PRAGMA application_id = 413;
+
+    CREATE TABLE t1(a INTEGER PRIMARY KEY AUTOINCREMENT, b);
+    CREATE INDEX i1 ON t1(b);
+    INSERT INTO t1 VALUES(NULL, 'one');
+    INSERT INTO t1 VALUES(NULL, 'two');
+    INSERT INTO t1 VALUES(NULL, 'three');
+    INSERT INTO t1 VALUES(NULL, 'four');
+    INSERT INTO t1 VALUES(NULL, 'five');
+    INSERT INTO t1 VALUES(NULL, 'six');
+
+    PRAGMA main.page_size;
+    PRAGMA main.auto_vacuum;
+    PRAGMA main.user_version;
+    PRAGMA main.application_id;
+  } {8192 2 412 413}
+
+  do_rbu_vacuum_test 1.9.1 $step
+  do_execsql_test 1.9.2 {
+    PRAGMA main.page_size;
+    PRAGMA main.auto_vacuum;
+    PRAGMA main.user_version;
+    PRAGMA main.application_id;
+  } {8192 2 412 413}
+
+  # Vacuum a database with a large sqlite_master table.
+  #
+  reset_db
+  do_test 1.10.1 {
+    for {set i 1} {$i < 50} {incr i} {
+      execsql "PRAGMA page_size = 1024"
+      execsql "CREATE TABLE t$i (a, b, c, PRIMARY KEY(a, b));"
+      execsql "
+        INSERT INTO t$i VALUES(1, 2, 3);
+        INSERT INTO t$i VALUES(4, 5, 6);
+      "
+    }
+  } {}
+  do_rbu_vacuum_test 1.10.2 $step
+}
+
+#-------------------------------------------------------------------------
+# Test some error cases:
+#
+#   2.1.* the db being vacuumed being in wal mode already.
+#   2.2.* database modified mid vacuum.
+#
+reset_db
+do_execsql_test 2.1.0 {
+  CREATE TABLE t1(a, b);
+  INSERT INTO t1 VALUES(1, 2);
+  INSERT INTO t1 VALUES(3, 4);
+  INSERT INTO t1 VALUES(5, 6);
+  INSERT INTO t1 VALUES(7, 8);
+  PRAGMA journal_mode = wal;
+  INSERT INTO t1 VALUES(9, 10);
+} wal
+do_test 2.1.1 {
+  sqlite3rbu_vacuum rbu test.db state.db
+  rbu step
+} {SQLITE_ERROR}
+do_test 2.1.2 {
+  list [catch { rbu close } msg] $msg
+} {1 {SQLITE_ERROR - cannot vacuum wal mode database}}
+
+reset_db
+do_execsql_test 2.2.0 {
+  CREATE TABLE tx(a PRIMARY KEY, b BLOB);
+  INSERT INTO tx VALUES(1, randomblob(900));
+  INSERT INTO tx SELECT a+1, randomblob(900) FROM tx;
+  INSERT INTO tx SELECT a+2, randomblob(900) FROM tx;
+  INSERT INTO tx SELECT a+4, randomblob(900) FROM tx;
+  INSERT INTO tx SELECT a+8, randomblob(900) FROM tx;
+}
+db_save_and_close
+for {set i 1} 1 {incr i} {
+  db_restore_and_reopen
+
+  sqlite3rbu_vacuum rbu test.db state.db
+  for {set step 0} {$step<$i} {incr step} { rbu step }
+  rbu close
+  if {[file exists test.db-wal]} break
+
+  execsql { INSERT INTO tx VALUES(20, 20) }
+
+  do_test 2.2.$i.1 {
+    sqlite3rbu_vacuum rbu test.db state.db 
+    rbu step
+  } {SQLITE_BUSY}
+  do_test 2.2.$i.2 {
+    list [catch { rbu close } msg] $msg
+  } {1 {SQLITE_BUSY - database modified during rbu vacuum}}
+}
+
+catch { db close }
+finish_test
+

Index: ext/rbu/sqlite3rbu.c
==================================================================
--- ext/rbu/sqlite3rbu.c
+++ ext/rbu/sqlite3rbu.c
@@ -174,10 +174,11 @@
 typedef struct rbu_file rbu_file;
 typedef struct RbuUpdateStmt RbuUpdateStmt;
 
 #if !defined(SQLITE_AMALGAMATION)
 typedef unsigned int u32;
+typedef unsigned short u16;
 typedef unsigned char u8;
 typedef sqlite3_int64 i64;
 #endif
 
 /*
@@ -186,10 +187,12 @@
 ** format.
 */
 #define WAL_LOCK_WRITE  0
 #define WAL_LOCK_CKPT   1
 #define WAL_LOCK_READ0  3
+
+#define SQLITE_FCNTL_RBUCNT    5149216
 
 /*
 ** A structure to store values read from the rbu_state table in memory.
 */
 struct RbuState {
@@ -365,10 +368,14 @@
   int nFrameAlloc;                /* Allocated size of aFrame[] array */
   RbuFrame *aFrame;
   int pgsz;
   u8 *aBuf;
   i64 iWalCksum;
+
+  /* Used in RBU vacuum mode only */
+  int nRbu;                       /* Number of RBU VFS in the stack */
+  rbu_file *pRbuFd;               /* Fd for main db of dbRbu */
 };
 
 /*
 ** An rbu VFS is implemented using an instance of this structure.
 */
@@ -390,10 +397,11 @@
   sqlite3rbu *pRbu;               /* Pointer to rbu object (rbu target only) */
 
   int openFlags;                  /* Flags this file was opened with */
   u32 iCookie;                    /* Cookie value for main db files */
   u8 iWriteVer;                   /* "write-version" value for main db files */
+  u8 bNolock;                     /* True to fail EXCLUSIVE locks */
 
   int nShm;                       /* Number of entries in apShm[] array */
   char **apShm;                   /* Array of mmap'd *-shm regions */
   char *zDel;                     /* Delete this when closing file */
 
@@ -400,10 +408,15 @@
   const char *zWal;               /* Wal filename for this main db file */
   rbu_file *pWalFd;               /* Wal file descriptor for this main db */
   rbu_file *pMainNext;            /* Next MAIN_DB file */
 };
 
+/*
+** True for an RBU vacuum handle, or false otherwise.
+*/
+#define rbuIsVacuum(p) ((p)->zTarget==0)
+
 
 /*************************************************************************
 ** The following three functions, found below:
 **
 **   rbuDeltaGetInt()
@@ -848,12 +861,15 @@
 }
 
 
 /*
 ** The implementation of the rbu_target_name() SQL function. This function
-** accepts one argument - the name of a table in the RBU database. If the
-** table name matches the pattern:
+** accepts one or two arguments. The first argument is the name of a table -
+** the name of a table in the RBU database.  The second, if it is present, is 1
+** for a view or 0 for a table. 
+**
+** For a non-vacuum RBU handle, if the table name matches the pattern:
 **
 **     data[0-9]_<name>
 **
 ** where <name> is any sequence of 1 or more characters, <name> is returned.
 ** Otherwise, if the only argument does not match the above pattern, an SQL
@@ -860,25 +876,37 @@
 ** NULL is returned.
 **
 **     "data_t1"     -> "t1"
 **     "data0123_t2" -> "t2"
 **     "dataAB_t3"   -> NULL
+**
+** For an rbu vacuum handle, a copy of the first argument is returned if
+** the second argument is either missing or 0 (not a view).
 */
 static void rbuTargetNameFunc(
-  sqlite3_context *context,
+  sqlite3_context *pCtx,
   int argc,
   sqlite3_value **argv
 ){
+  sqlite3rbu *p = sqlite3_user_data(pCtx);
   const char *zIn;
-  assert( argc==1 );
+  assert( argc==1 || argc==2 );
 
   zIn = (const char*)sqlite3_value_text(argv[0]);
-  if( zIn && strlen(zIn)>4 && memcmp("data", zIn, 4)==0 ){
-    int i;
-    for(i=4; zIn[i]>='0' && zIn[i]<='9'; i++);
-    if( zIn[i]=='_' && zIn[i+1] ){
-      sqlite3_result_text(context, &zIn[i+1], -1, SQLITE_STATIC);
+  if( zIn ){
+    if( rbuIsVacuum(p) ){
+      if( argc==1 || 0==sqlite3_value_int(argv[1]) ){
+        sqlite3_result_text(pCtx, zIn, -1, SQLITE_STATIC);
+      }
+    }else{
+      if( strlen(zIn)>4 && memcmp("data", zIn, 4)==0 ){
+        int i;
+        for(i=4; zIn[i]>='0' && zIn[i]<='9'; i++);
+        if( zIn[i]=='_' && zIn[i+1] ){
+          sqlite3_result_text(pCtx, &zIn[i+1], -1, SQLITE_STATIC);
+        }
+      }
     }
   }
 }
 
 /*
@@ -892,11 +920,12 @@
 static int rbuObjIterFirst(sqlite3rbu *p, RbuObjIter *pIter){
   int rc;
   memset(pIter, 0, sizeof(RbuObjIter));
 
   rc = prepareAndCollectError(p->dbRbu, &pIter->pTblIter, &p->zErrmsg, 
-      "SELECT rbu_target_name(name) AS target, name FROM sqlite_master "
+      "SELECT rbu_target_name(name, type='view') AS target, name "
+      "FROM sqlite_master "
       "WHERE type IN ('table', 'view') AND target IS NOT NULL "
       "ORDER BY name"
   );
 
   if( rc==SQLITE_OK ){
@@ -1268,10 +1297,11 @@
     }
     sqlite3_finalize(pStmt);
     pStmt = 0;
 
     if( p->rc==SQLITE_OK
+     && rbuIsVacuum(p)==0
      && bRbuRowid!=(pIter->eType==RBU_PK_VTAB || pIter->eType==RBU_PK_NONE)
     ){
       p->rc = SQLITE_ERROR;
       p->zErrmsg = sqlite3_mprintf(
           "table %q %s rbu_rowid column", pIter->zDataTbl,
@@ -1407,10 +1437,12 @@
       if( pIter->eType==RBU_PK_IPK ){
         int i;
         for(i=0; pIter->abTblPk[i]==0; i++);
         assert( i<pIter->nTblCol );
         zCol = pIter->azTblCol[i];
+      }else if( rbuIsVacuum(p) ){
+        zCol = "_rowid_";
       }else{
         zCol = "rbu_rowid";
       }
       zType = "INTEGER";
     }else{
@@ -1947,20 +1979,29 @@
           sqlite3_mprintf("INSERT INTO \"rbu_imp_%w\" VALUES(%s)", zTbl, zBind)
         );
       }
 
       /* And to delete index entries */
-      if( p->rc==SQLITE_OK ){
+      if( rbuIsVacuum(p)==0 && p->rc==SQLITE_OK ){
         p->rc = prepareFreeAndCollectError(
             p->dbMain, &pIter->pDelete, &p->zErrmsg,
           sqlite3_mprintf("DELETE FROM \"rbu_imp_%w\" WHERE %s", zTbl, zWhere)
         );
       }
 
       /* Create the SELECT statement to read keys in sorted order */
       if( p->rc==SQLITE_OK ){
         char *zSql;
+        if( rbuIsVacuum(p) ){
+          zSql = sqlite3_mprintf(
+              "SELECT %s, 0 AS rbu_control FROM '%q' ORDER BY %s%s",
+              zCollist, 
+              pIter->zDataTbl,
+              zCollist, zLimit
+          );
+        }else
+
         if( pIter->eType==RBU_PK_EXTERNAL || pIter->eType==RBU_PK_NONE ){
           zSql = sqlite3_mprintf(
               "SELECT %s, rbu_control FROM %s.'rbu_tmp_%q' ORDER BY %s%s",
               zCollist, p->zStateDb, pIter->zDataTbl,
               zCollist, zLimit
@@ -1983,11 +2024,13 @@
       sqlite3_free(zImposterCols);
       sqlite3_free(zImposterPK);
       sqlite3_free(zWhere);
       sqlite3_free(zBind);
     }else{
-      int bRbuRowid = (pIter->eType==RBU_PK_VTAB || pIter->eType==RBU_PK_NONE);
+      int bRbuRowid = (pIter->eType==RBU_PK_VTAB)
+                    ||(pIter->eType==RBU_PK_NONE)
+                    ||(pIter->eType==RBU_PK_EXTERNAL && rbuIsVacuum(p));
       const char *zTbl = pIter->zTbl;       /* Table this step applies to */
       const char *zWrite;                   /* Imposter table name */
 
       char *zBindings = rbuObjIterGetBindlist(p, pIter->nTblCol + bRbuRowid);
       char *zWhere = rbuObjIterGetWhere(p, pIter);
@@ -2010,20 +2053,22 @@
               zWrite, zTbl, zCollist, (bRbuRowid ? ", _rowid_" : ""), zBindings
             )
         );
       }
 
-      /* Create the DELETE statement to write to the target PK b-tree */
-      if( p->rc==SQLITE_OK ){
+      /* Create the DELETE statement to write to the target PK b-tree.
+      ** Because it only performs INSERT operations, this is not required for
+      ** an rbu vacuum handle.  */
+      if( rbuIsVacuum(p)==0 && p->rc==SQLITE_OK ){
         p->rc = prepareFreeAndCollectError(p->dbMain, &pIter->pDelete, pz,
             sqlite3_mprintf(
               "DELETE FROM \"%s%w\" WHERE %s", zWrite, zTbl, zWhere
             )
         );
       }
 
-      if( pIter->abIndexed ){
+      if( rbuIsVacuum(p)==0 && pIter->abIndexed ){
         const char *zRbuRowid = "";
         if( pIter->eType==RBU_PK_EXTERNAL || pIter->eType==RBU_PK_NONE ){
           zRbuRowid = ", rbu_rowid";
         }
 
@@ -2069,14 +2114,20 @@
         rbuObjIterPrepareTmpInsert(p, pIter, zCollist, zRbuRowid);
       }
 
       /* Create the SELECT statement to read keys from data_xxx */
       if( p->rc==SQLITE_OK ){
+        const char *zRbuRowid = "";
+        if( bRbuRowid ){
+          zRbuRowid = rbuIsVacuum(p) ? ",_rowid_ " : ",rbu_rowid";
+        }
         p->rc = prepareFreeAndCollectError(p->dbRbu, &pIter->pSelect, pz,
             sqlite3_mprintf(
-              "SELECT %s, rbu_control%s FROM '%q'%s", 
-              zCollist, (bRbuRowid ? ", rbu_rowid" : ""), 
+              "SELECT %s,%s rbu_control%s FROM '%q'%s", 
+              zCollist, 
+              (rbuIsVacuum(p) ? "0 AS " : ""),
+              zRbuRowid,
               pIter->zDataTbl, zLimit
             )
         );
       }
 
@@ -2167,44 +2218,231 @@
   }
 
   return p->rc;
 }
 
-static sqlite3 *rbuOpenDbhandle(sqlite3rbu *p, const char *zName){
+static sqlite3 *rbuOpenDbhandle(
+  sqlite3rbu *p, 
+  const char *zName, 
+  int bUseVfs
+){
   sqlite3 *db = 0;
   if( p->rc==SQLITE_OK ){
     const int flags = SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_URI;
-    p->rc = sqlite3_open_v2(zName, &db, flags, p->zVfsName);
+    p->rc = sqlite3_open_v2(zName, &db, flags, bUseVfs ? p->zVfsName : 0);
     if( p->rc ){
       p->zErrmsg = sqlite3_mprintf("%s", sqlite3_errmsg(db));
       sqlite3_close(db);
       db = 0;
     }
   }
   return db;
 }
+
+/*
+** Free an RbuState object allocated by rbuLoadState().
+*/
+static void rbuFreeState(RbuState *p){
+  if( p ){
+    sqlite3_free(p->zTbl);
+    sqlite3_free(p->zIdx);
+    sqlite3_free(p);
+  }
+}
+
+/*
+** Allocate an RbuState object and load the contents of the rbu_state 
+** table into it. Return a pointer to the new object. It is the 
+** responsibility of the caller to eventually free the object using
+** sqlite3_free().
+**
+** If an error occurs, leave an error code and message in the rbu handle
+** and return NULL.
+*/
+static RbuState *rbuLoadState(sqlite3rbu *p){
+  RbuState *pRet = 0;
+  sqlite3_stmt *pStmt = 0;
+  int rc;
+  int rc2;
+
+  pRet = (RbuState*)rbuMalloc(p, sizeof(RbuState));
+  if( pRet==0 ) return 0;
+
+  rc = prepareFreeAndCollectError(p->dbRbu, &pStmt, &p->zErrmsg, 
+      sqlite3_mprintf("SELECT k, v FROM %s.rbu_state", p->zStateDb)
+  );
+  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+    switch( sqlite3_column_int(pStmt, 0) ){
+      case RBU_STATE_STAGE:
+        pRet->eStage = sqlite3_column_int(pStmt, 1);
+        if( pRet->eStage!=RBU_STAGE_OAL
+         && pRet->eStage!=RBU_STAGE_MOVE
+         && pRet->eStage!=RBU_STAGE_CKPT
+        ){
+          p->rc = SQLITE_CORRUPT;
+        }
+        break;
+
+      case RBU_STATE_TBL:
+        pRet->zTbl = rbuStrndup((char*)sqlite3_column_text(pStmt, 1), &rc);
+        break;
+
+      case RBU_STATE_IDX:
+        pRet->zIdx = rbuStrndup((char*)sqlite3_column_text(pStmt, 1), &rc);
+        break;
+
+      case RBU_STATE_ROW:
+        pRet->nRow = sqlite3_column_int(pStmt, 1);
+        break;
+
+      case RBU_STATE_PROGRESS:
+        pRet->nProgress = sqlite3_column_int64(pStmt, 1);
+        break;
+
+      case RBU_STATE_CKPT:
+        pRet->iWalCksum = sqlite3_column_int64(pStmt, 1);
+        break;
+
+      case RBU_STATE_COOKIE:
+        pRet->iCookie = (u32)sqlite3_column_int64(pStmt, 1);
+        break;
+
+      case RBU_STATE_OALSZ:
+        pRet->iOalSz = (u32)sqlite3_column_int64(pStmt, 1);
+        break;
+
+      case RBU_STATE_PHASEONESTEP:
+        pRet->nPhaseOneStep = sqlite3_column_int64(pStmt, 1);
+        break;
+
+      default:
+        rc = SQLITE_CORRUPT;
+        break;
+    }
+  }
+  rc2 = sqlite3_finalize(pStmt);
+  if( rc==SQLITE_OK ) rc = rc2;
+
+  p->rc = rc;
+  return pRet;
+}
+
 
 /*
 ** Open the database handle and attach the RBU database as "rbu". If an
 ** error occurs, leave an error code and message in the RBU handle.
 */
 static void rbuOpenDatabase(sqlite3rbu *p){
   assert( p->rc==SQLITE_OK );
   assert( p->dbMain==0 && p->dbRbu==0 );
+  assert( rbuIsVacuum(p) || p->zTarget!=0 );
 
-  p->eStage = 0;
-  p->dbMain = rbuOpenDbhandle(p, p->zTarget);
-  p->dbRbu = rbuOpenDbhandle(p, p->zRbu);
+  /* Open the RBU database */
+  p->dbRbu = rbuOpenDbhandle(p, p->zRbu, 1);
+
+  if( p->rc==SQLITE_OK && rbuIsVacuum(p) ){
+    sqlite3_file_control(p->dbRbu, "main", SQLITE_FCNTL_RBUCNT, (void*)p);
+  }
 
   /* If using separate RBU and state databases, attach the state database to
   ** the RBU db handle now.  */
   if( p->zState ){
     rbuMPrintfExec(p, p->dbRbu, "ATTACH %Q AS stat", p->zState);
     memcpy(p->zStateDb, "stat", 4);
   }else{
     memcpy(p->zStateDb, "main", 4);
   }
+
+#if 0
+  if( p->rc==SQLITE_OK && rbuIsVacuum(p) ){
+    p->rc = sqlite3_exec(p->dbRbu, "BEGIN", 0, 0, 0);
+  }
+#endif
+
+  /* If it has not already been created, create the rbu_state table */
+  rbuMPrintfExec(p, p->dbRbu, RBU_CREATE_STATE, p->zStateDb);
+
+#if 0
+  if( rbuIsVacuum(p) ){
+    if( p->rc==SQLITE_OK ){
+      int rc2;
+      int bOk = 0;
+      sqlite3_stmt *pCnt = 0;
+      p->rc = prepareAndCollectError(p->dbRbu, &pCnt, &p->zErrmsg,
+          "SELECT count(*) FROM stat.sqlite_master"
+      );
+      if( p->rc==SQLITE_OK 
+       && sqlite3_step(pCnt)==SQLITE_ROW
+       && 1==sqlite3_column_int(pCnt, 0)
+      ){
+        bOk = 1;
+      }
+      rc2 = sqlite3_finalize(pCnt);
+      if( p->rc==SQLITE_OK ) p->rc = rc2;
+
+      if( p->rc==SQLITE_OK && bOk==0 ){
+        p->rc = SQLITE_ERROR;
+        p->zErrmsg = sqlite3_mprintf("invalid state database");
+      }
+    
+      if( p->rc==SQLITE_OK ){
+        p->rc = sqlite3_exec(p->dbRbu, "COMMIT", 0, 0, 0);
+      }
+    }
+  }
+#endif
+
+  if( p->rc==SQLITE_OK && rbuIsVacuum(p) ){
+    int bOpen = 0;
+    int rc;
+    p->nRbu = 0;
+    p->pRbuFd = 0;
+    rc = sqlite3_file_control(p->dbRbu, "main", SQLITE_FCNTL_RBUCNT, (void*)p);
+    if( rc!=SQLITE_NOTFOUND ) p->rc = rc;
+    if( p->eStage>=RBU_STAGE_MOVE ){
+      bOpen = 1;
+    }else{
+      RbuState *pState = rbuLoadState(p);
+      if( pState ){
+        bOpen = (pState->eStage>RBU_STAGE_MOVE);
+        rbuFreeState(pState);
+      }
+    }
+    if( bOpen ) p->dbMain = rbuOpenDbhandle(p, p->zRbu, p->nRbu<=1);
+  }
+
+  p->eStage = 0;
+  if( p->rc==SQLITE_OK && p->dbMain==0 ){
+    if( !rbuIsVacuum(p) ){
+      p->dbMain = rbuOpenDbhandle(p, p->zTarget, 1);
+    }else if( p->pRbuFd->pWalFd ){
+      p->rc = SQLITE_ERROR;
+      p->zErrmsg = sqlite3_mprintf("cannot vacuum wal mode database");
+    }else{
+      char *zTarget;
+      char *zExtra = 0;
+      if( strlen(p->zRbu)>=5 && 0==memcmp("file:", p->zRbu, 5) ){
+        zExtra = &p->zRbu[5];
+        while( *zExtra ){
+          if( *zExtra++=='?' ) break;
+        }
+        if( *zExtra=='\0' ) zExtra = 0;
+      }
+
+      zTarget = sqlite3_mprintf("file:%s-vacuum?rbu_memory=1%s%s", 
+          sqlite3_db_filename(p->dbRbu, "main"),
+          (zExtra==0 ? "" : "&"), (zExtra==0 ? "" : zExtra)
+      );
+
+      if( zTarget==0 ){
+        p->rc = SQLITE_NOMEM;
+        return;
+      }
+      p->dbMain = rbuOpenDbhandle(p, zTarget, p->nRbu<=1);
+      sqlite3_free(zTarget);
+    }
+  }
 
   if( p->rc==SQLITE_OK ){
     p->rc = sqlite3_create_function(p->dbMain, 
         "rbu_tmp_insert", -1, SQLITE_UTF8, (void*)p, rbuTmpInsertFunc, 0, 0
     );
@@ -2216,11 +2454,11 @@
     );
   }
 
   if( p->rc==SQLITE_OK ){
     p->rc = sqlite3_create_function(p->dbRbu, 
-        "rbu_target_name", 1, SQLITE_UTF8, (void*)p, rbuTargetNameFunc, 0, 0
+        "rbu_target_name", -1, SQLITE_UTF8, (void*)p, rbuTargetNameFunc, 0, 0
     );
   }
 
   if( p->rc==SQLITE_OK ){
     p->rc = sqlite3_file_control(p->dbMain, "main", SQLITE_FCNTL_RBU, (void*)p);
@@ -2475,13 +2713,19 @@
 ** If an error occurs, leave an error code and error message in the rbu 
 ** handle.
 */
 static void rbuMoveOalFile(sqlite3rbu *p){
   const char *zBase = sqlite3_db_filename(p->dbMain, "main");
+  const char *zMove = zBase;
+  char *zOal;
+  char *zWal;
 
-  char *zWal = sqlite3_mprintf("%s-wal", zBase);
-  char *zOal = sqlite3_mprintf("%s-oal", zBase);
+  if( rbuIsVacuum(p) ){
+    zMove = sqlite3_db_filename(p->dbRbu, "main");
+  }
+  zOal = sqlite3_mprintf("%s-oal", zMove);
+  zWal = sqlite3_mprintf("%s-wal", zMove);
 
   assert( p->eStage==RBU_STAGE_MOVE );
   assert( p->rc==SQLITE_OK && p->zErrmsg==0 );
   if( zWal==0 || zOal==0 ){
     p->rc = SQLITE_NOMEM;
@@ -2498,12 +2742,12 @@
       rbuFileSuffix3(zBase, zWal);
       rbuFileSuffix3(zBase, zOal);
 
       /* Re-open the databases. */
       rbuObjIterFinalize(&p->objiter);
-      sqlite3_close(p->dbMain);
       sqlite3_close(p->dbRbu);
+      sqlite3_close(p->dbMain);
       p->dbMain = 0;
       p->dbRbu = 0;
 
 #if defined(_WIN32_WCE)
       {
@@ -2661,23 +2905,28 @@
 
     pVal = sqlite3_column_value(pIter->pSelect, i);
     p->rc = sqlite3_bind_value(pWriter, i+1, pVal);
     if( p->rc ) return;
   }
-  if( pIter->zIdx==0
-   && (pIter->eType==RBU_PK_VTAB || pIter->eType==RBU_PK_NONE) 
-  ){
-    /* For a virtual table, or a table with no primary key, the 
-    ** SELECT statement is:
-    **
-    **   SELECT <cols>, rbu_control, rbu_rowid FROM ....
-    **
-    ** Hence column_value(pIter->nCol+1).
-    */
-    assertColumnName(pIter->pSelect, pIter->nCol+1, "rbu_rowid");
-    pVal = sqlite3_column_value(pIter->pSelect, pIter->nCol+1);
-    p->rc = sqlite3_bind_value(pWriter, pIter->nCol+1, pVal);
+  if( pIter->zIdx==0 ){
+    if( pIter->eType==RBU_PK_VTAB 
+     || pIter->eType==RBU_PK_NONE 
+     || (pIter->eType==RBU_PK_EXTERNAL && rbuIsVacuum(p)) 
+    ){
+      /* For a virtual table, or a table with no primary key, the 
+      ** SELECT statement is:
+      **
+      **   SELECT <cols>, rbu_control, rbu_rowid FROM ....
+      **
+      ** Hence column_value(pIter->nCol+1).
+      */
+      assertColumnName(pIter->pSelect, pIter->nCol+1, 
+          rbuIsVacuum(p) ? "rowid" : "rbu_rowid"
+      );
+      pVal = sqlite3_column_value(pIter->pSelect, pIter->nCol+1);
+      p->rc = sqlite3_bind_value(pWriter, pIter->nCol+1, pVal);
+    }
   }
   if( p->rc==SQLITE_OK ){
     sqlite3_step(pWriter);
     p->rc = resetAndCollectError(pWriter, &p->zErrmsg);
   }
@@ -2752,17 +3001,22 @@
   return p->rc;
 }
 
 /*
 ** Increment the schema cookie of the main database opened by p->dbMain.
+**
+** Or, if this is an RBU vacuum, set the schema cookie of the main db
+** opened by p->dbMain to one more than the schema cookie of the main
+** db opened by p->dbRbu.
 */
 static void rbuIncrSchemaCookie(sqlite3rbu *p){
   if( p->rc==SQLITE_OK ){
+    sqlite3 *dbread = (rbuIsVacuum(p) ? p->dbRbu : p->dbMain);
     int iCookie = 1000000;
     sqlite3_stmt *pStmt;
 
-    p->rc = prepareAndCollectError(p->dbMain, &pStmt, &p->zErrmsg, 
+    p->rc = prepareAndCollectError(dbread, &pStmt, &p->zErrmsg, 
         "PRAGMA schema_version"
     );
     if( p->rc==SQLITE_OK ){
       /* Coverage: it may be that this sqlite3_step() cannot fail. There
       ** is already a transaction open, so the prepared statement cannot
@@ -2786,10 +3040,11 @@
 ** are determined by inspecting the rbu handle passed as the first argument.
 */
 static void rbuSaveState(sqlite3rbu *p, int eStage){
   if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
     sqlite3_stmt *pInsert = 0;
+    rbu_file *pFd = (rbuIsVacuum(p) ? p->pRbuFd : p->pTargetFd);
     int rc;
 
     assert( p->zErrmsg==0 );
     rc = prepareFreeAndCollectError(p->dbRbu, &pInsert, &p->zErrmsg, 
         sqlite3_mprintf(
@@ -2808,11 +3063,11 @@
           RBU_STATE_TBL, p->objiter.zTbl, 
           RBU_STATE_IDX, p->objiter.zIdx, 
           RBU_STATE_ROW, p->nStep, 
           RBU_STATE_PROGRESS, p->nProgress,
           RBU_STATE_CKPT, p->iWalCksum,
-          RBU_STATE_COOKIE, (i64)p->pTargetFd->iCookie,
+          RBU_STATE_COOKIE, (i64)pFd->iCookie,
           RBU_STATE_OALSZ, p->iOalSz,
           RBU_STATE_PHASEONESTEP, p->nPhaseOneStep
       )
     );
     assert( pInsert==0 || rc==SQLITE_OK );
@@ -2838,11 +3093,11 @@
 
           if( pIter->bCleanup ){
             /* Clean up the rbu_tmp_xxx table for the previous table. It 
             ** cannot be dropped as there are currently active SQL statements.
             ** But the contents can be deleted.  */
-            if( pIter->abIndexed ){
+            if( rbuIsVacuum(p)==0 && pIter->abIndexed ){
               rbuMPrintfExec(p, p->dbRbu, 
                   "DELETE FROM %s.'rbu_tmp_%q'", p->zStateDb, pIter->zDataTbl
               );
             }
           }else{
@@ -2925,98 +3180,10 @@
   }else{
     return SQLITE_NOMEM;
   }
 }
 
-/*
-** Free an RbuState object allocated by rbuLoadState().
-*/
-static void rbuFreeState(RbuState *p){
-  if( p ){
-    sqlite3_free(p->zTbl);
-    sqlite3_free(p->zIdx);
-    sqlite3_free(p);
-  }
-}
-
-/*
-** Allocate an RbuState object and load the contents of the rbu_state 
-** table into it. Return a pointer to the new object. It is the 
-** responsibility of the caller to eventually free the object using
-** sqlite3_free().
-**
-** If an error occurs, leave an error code and message in the rbu handle
-** and return NULL.
-*/
-static RbuState *rbuLoadState(sqlite3rbu *p){
-  RbuState *pRet = 0;
-  sqlite3_stmt *pStmt = 0;
-  int rc;
-  int rc2;
-
-  pRet = (RbuState*)rbuMalloc(p, sizeof(RbuState));
-  if( pRet==0 ) return 0;
-
-  rc = prepareFreeAndCollectError(p->dbRbu, &pStmt, &p->zErrmsg, 
-      sqlite3_mprintf("SELECT k, v FROM %s.rbu_state", p->zStateDb)
-  );
-  while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
-    switch( sqlite3_column_int(pStmt, 0) ){
-      case RBU_STATE_STAGE:
-        pRet->eStage = sqlite3_column_int(pStmt, 1);
-        if( pRet->eStage!=RBU_STAGE_OAL
-         && pRet->eStage!=RBU_STAGE_MOVE
-         && pRet->eStage!=RBU_STAGE_CKPT
-        ){
-          p->rc = SQLITE_CORRUPT;
-        }
-        break;
-
-      case RBU_STATE_TBL:
-        pRet->zTbl = rbuStrndup((char*)sqlite3_column_text(pStmt, 1), &rc);
-        break;
-
-      case RBU_STATE_IDX:
-        pRet->zIdx = rbuStrndup((char*)sqlite3_column_text(pStmt, 1), &rc);
-        break;
-
-      case RBU_STATE_ROW:
-        pRet->nRow = sqlite3_column_int(pStmt, 1);
-        break;
-
-      case RBU_STATE_PROGRESS:
-        pRet->nProgress = sqlite3_column_int64(pStmt, 1);
-        break;
-
-      case RBU_STATE_CKPT:
-        pRet->iWalCksum = sqlite3_column_int64(pStmt, 1);
-        break;
-
-      case RBU_STATE_COOKIE:
-        pRet->iCookie = (u32)sqlite3_column_int64(pStmt, 1);
-        break;
-
-      case RBU_STATE_OALSZ:
-        pRet->iOalSz = (u32)sqlite3_column_int64(pStmt, 1);
-        break;
-
-      case RBU_STATE_PHASEONESTEP:
-        pRet->nPhaseOneStep = sqlite3_column_int64(pStmt, 1);
-        break;
-
-      default:
-        rc = SQLITE_CORRUPT;
-        break;
-    }
-  }
-  rc2 = sqlite3_finalize(pStmt);
-  if( rc==SQLITE_OK ) rc = rc2;
-
-  p->rc = rc;
-  return pRet;
-}
-
 /*
 ** Compare strings z1 and z2, returning 0 if they are identical, or non-zero
 ** otherwise. Either or both argument may be NULL. Two NULL values are
 ** considered equal, and NULL is considered distinct from all other values.
 */
@@ -3203,19 +3370,103 @@
     }
   }
 }
 
 /*
-** Open and return a new RBU handle. 
+** The second argument passed to this function is the name of a PRAGMA 
+** setting - "page_size", "auto_vacuum", "user_version" or "application_id".
+** This function executes the following on sqlite3rbu.dbRbu:
+**
+**   "PRAGMA main.$zPragma"
+**
+** where $zPragma is the string passed as the second argument, then
+** on sqlite3rbu.dbMain:
+**
+**   "PRAGMA main.$zPragma = $val"
+**
+** where $val is the value returned by the first PRAGMA invocation.
+**
+** In short, it copies the value  of the specified PRAGMA setting from
+** dbRbu to dbMain.
+*/
+static void rbuCopyPragma(sqlite3rbu *p, const char *zPragma){
+  if( p->rc==SQLITE_OK ){
+    sqlite3_stmt *pPragma = 0;
+    p->rc = prepareFreeAndCollectError(p->dbRbu, &pPragma, &p->zErrmsg, 
+        sqlite3_mprintf("PRAGMA main.%s", zPragma)
+    );
+    if( p->rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pPragma) ){
+      p->rc = rbuMPrintfExec(p, p->dbMain, "PRAGMA main.%s = %d",
+          zPragma, sqlite3_column_int(pPragma, 0)
+      );
+    }
+    rbuFinalize(p, pPragma);
+  }
+}
+
+/*
+** The RBU handle passed as the only argument has just been opened and 
+** the state database is empty. If this RBU handle was opened for an
+** RBU vacuum operation, create the schema in the target db.
 */
-sqlite3rbu *sqlite3rbu_open(
+static void rbuCreateTargetSchema(sqlite3rbu *p){
+  sqlite3_stmt *pSql = 0;
+  sqlite3_stmt *pInsert = 0;
+
+  assert( rbuIsVacuum(p) );
+  p->rc = sqlite3_exec(p->dbMain, "PRAGMA writable_schema=1", 0,0, &p->zErrmsg);
+  if( p->rc==SQLITE_OK ){
+    p->rc = prepareAndCollectError(p->dbRbu, &pSql, &p->zErrmsg, 
+      "SELECT sql FROM sqlite_master WHERE sql!='' AND rootpage!=0"
+      " AND name!='sqlite_sequence' "
+      " ORDER BY type DESC"
+    );
+  }
+
+  while( p->rc==SQLITE_OK && sqlite3_step(pSql)==SQLITE_ROW ){
+    const char *zSql = (const char*)sqlite3_column_text(pSql, 0);
+    p->rc = sqlite3_exec(p->dbMain, zSql, 0, 0, &p->zErrmsg);
+  }
+  rbuFinalize(p, pSql);
+  if( p->rc!=SQLITE_OK ) return;
+
+  if( p->rc==SQLITE_OK ){
+    p->rc = prepareAndCollectError(p->dbRbu, &pSql, &p->zErrmsg, 
+        "SELECT * FROM sqlite_master WHERE rootpage=0 OR rootpage IS NULL" 
+    );
+  }
+
+  if( p->rc==SQLITE_OK ){
+    p->rc = prepareAndCollectError(p->dbMain, &pInsert, &p->zErrmsg, 
+        "INSERT INTO sqlite_master VALUES(?,?,?,?,?)"
+    );
+  }
+
+  while( p->rc==SQLITE_OK && sqlite3_step(pSql)==SQLITE_ROW ){
+    int i;
+    for(i=0; i<5; i++){
+      sqlite3_bind_value(pInsert, i+1, sqlite3_column_value(pSql, i));
+    }
+    sqlite3_step(pInsert);
+    p->rc = sqlite3_reset(pInsert);
+  }
+  if( p->rc==SQLITE_OK ){
+    p->rc = sqlite3_exec(p->dbMain, "PRAGMA writable_schema=0",0,0,&p->zErrmsg);
+  }
+
+  rbuFinalize(p, pSql);
+  rbuFinalize(p, pInsert);
+}
+
+
+static sqlite3rbu *openRbuHandle(
   const char *zTarget, 
   const char *zRbu,
   const char *zState
 ){
   sqlite3rbu *p;
-  size_t nTarget = strlen(zTarget);
+  size_t nTarget = zTarget ? strlen(zTarget) : 0;
   size_t nRbu = strlen(zRbu);
   size_t nState = zState ? strlen(zState) : 0;
   size_t nByte = sizeof(sqlite3rbu) + nTarget+1 + nRbu+1+ nState+1;
 
   p = (sqlite3rbu*)sqlite3_malloc64(nByte);
@@ -3224,26 +3475,28 @@
 
     /* Create the custom VFS. */
     memset(p, 0, sizeof(sqlite3rbu));
     rbuCreateVfs(p);
 
-    /* Open the target database */
+    /* Open the target, RBU and state databases */
     if( p->rc==SQLITE_OK ){
-      p->zTarget = (char*)&p[1];
-      memcpy(p->zTarget, zTarget, nTarget+1);
-      p->zRbu = &p->zTarget[nTarget+1];
+      char *pCsr = (char*)&p[1];
+      if( zTarget ){
+        p->zTarget = pCsr;
+        memcpy(p->zTarget, zTarget, nTarget+1);
+        pCsr += nTarget+1;
+      }
+      p->zRbu = pCsr;
       memcpy(p->zRbu, zRbu, nRbu+1);
+      pCsr += nRbu+1;
       if( zState ){
-        p->zState = &p->zRbu[nRbu+1];
+        p->zState = pCsr;
         memcpy(p->zState, zState, nState+1);
       }
       rbuOpenDatabase(p);
     }
 
-    /* If it has not already been created, create the rbu_state table */
-    rbuMPrintfExec(p, p->dbRbu, RBU_CREATE_STATE, p->zStateDb);
-
     if( p->rc==SQLITE_OK ){
       pState = rbuLoadState(p);
       assert( pState || p->rc!=SQLITE_OK );
       if( p->rc==SQLITE_OK ){
 
@@ -3269,31 +3522,43 @@
         p->eStage = RBU_STAGE_CKPT;
         p->nStep = 0;
       }
     }
 
-    if( p->rc==SQLITE_OK
+    if( p->rc==SQLITE_OK 
      && (p->eStage==RBU_STAGE_OAL || p->eStage==RBU_STAGE_MOVE)
-     && pState->eStage!=0 && p->pTargetFd->iCookie!=pState->iCookie
-    ){   
-      /* At this point (pTargetFd->iCookie) contains the value of the
-      ** change-counter cookie (the thing that gets incremented when a 
-      ** transaction is committed in rollback mode) currently stored on 
-      ** page 1 of the database file. */
-      p->rc = SQLITE_BUSY;
-      p->zErrmsg = sqlite3_mprintf("database modified during rbu update");
+     && pState->eStage!=0
+    ){
+      rbu_file *pFd = (rbuIsVacuum(p) ? p->pRbuFd : p->pTargetFd);
+      if( pFd->iCookie!=pState->iCookie ){   
+        /* At this point (pTargetFd->iCookie) contains the value of the
+        ** change-counter cookie (the thing that gets incremented when a 
+        ** transaction is committed in rollback mode) currently stored on 
+        ** page 1 of the database file. */
+        p->rc = SQLITE_BUSY;
+        p->zErrmsg = sqlite3_mprintf("database modified during rbu %s",
+            (rbuIsVacuum(p) ? "vacuum" : "update")
+        );
+      }
     }
 
     if( p->rc==SQLITE_OK ){
       if( p->eStage==RBU_STAGE_OAL ){
         sqlite3 *db = p->dbMain;
+
+        if( pState->eStage==0 && rbuIsVacuum(p) ){
+          rbuCopyPragma(p, "page_size");
+          rbuCopyPragma(p, "auto_vacuum");
+        }
 
         /* Open transactions both databases. The *-oal file is opened or
         ** created at this point. */
-        p->rc = sqlite3_exec(db, "BEGIN IMMEDIATE", 0, 0, &p->zErrmsg);
+        if( p->rc==SQLITE_OK ){
+          p->rc = sqlite3_exec(db, "BEGIN IMMEDIATE", 0, 0, &p->zErrmsg);
+        }
         if( p->rc==SQLITE_OK ){
-          p->rc = sqlite3_exec(p->dbRbu, "BEGIN IMMEDIATE", 0, 0, &p->zErrmsg);
+          p->rc = sqlite3_exec(p->dbRbu, "BEGIN", 0, 0, &p->zErrmsg);
         }
 
         /* Check if the main database is a zipvfs db. If it is, set the upper
         ** level pager to use "journal_mode=off". This prevents it from 
         ** generating a large journal using a temp file.  */
@@ -3301,10 +3566,18 @@
           int frc = sqlite3_file_control(db, "main", SQLITE_FCNTL_ZIPVFS, 0);
           if( frc==SQLITE_OK ){
             p->rc = sqlite3_exec(db, "PRAGMA journal_mode=off",0,0,&p->zErrmsg);
           }
         }
+
+        /* If this is an RBU vacuum operation and the state table was empty
+        ** when this handle was opened, create the target database schema. */
+        if( p->rc==SQLITE_OK && pState->eStage==0 && rbuIsVacuum(p) ){
+          rbuCreateTargetSchema(p);
+          rbuCopyPragma(p, "user_version");
+          rbuCopyPragma(p, "application_id");
+        }
 
         /* Point the object iterator at the first object */
         if( p->rc==SQLITE_OK ){
           p->rc = rbuObjIterFirst(p, &p->objiter);
         }
@@ -3334,10 +3607,32 @@
   }
 
   return p;
 }
 
+/*
+** Open and return a new RBU handle. 
+*/
+sqlite3rbu *sqlite3rbu_open(
+  const char *zTarget, 
+  const char *zRbu,
+  const char *zState
+){
+  /* TODO: Check that zTarget and zRbu are non-NULL */
+  return openRbuHandle(zTarget, zRbu, zState);
+}
+
+/*
+** Open a handle to begin or resume an RBU VACUUM operation.
+*/
+sqlite3rbu *sqlite3rbu_vacuum(
+  const char *zTarget, 
+  const char *zState
+){
+  /* TODO: Check that both arguments are non-NULL */
+  return openRbuHandle(0, zTarget, zState);
+}
 
 /*
 ** Return the database handle used by pRbu.
 */
 sqlite3 *sqlite3rbu_db(sqlite3rbu *pRbu, int bRbu){
@@ -3387,14 +3682,24 @@
       p->rc = sqlite3_exec(p->dbRbu, "COMMIT", 0, 0, &p->zErrmsg);
     }
 
     /* Close any open statement handles. */
     rbuObjIterFinalize(&p->objiter);
+
+    /* If this is an RBU vacuum handle and the vacuum has either finished
+    ** successfully or encountered an error, delete the contents of the 
+    ** state table. This causes the next call to sqlite3rbu_vacuum() 
+    ** specifying the current target and state databases to start a new
+    ** vacuum from scratch.  */
+    if( rbuIsVacuum(p) && p->rc!=SQLITE_OK && p->dbRbu ){
+      int rc2 = sqlite3_exec(p->dbRbu, "DELETE FROM stat.rbu_state", 0, 0, 0);
+      if( p->rc==SQLITE_DONE && rc2!=SQLITE_OK ) p->rc = rc2;
+    }
 
     /* Close the open database handle and VFS object. */
-    sqlite3_close(p->dbMain);
     sqlite3_close(p->dbRbu);
+    sqlite3_close(p->dbMain);
     rbuDeleteVfs(p);
     sqlite3_free(p->aBuf);
     sqlite3_free(p->aFrame);
 
     rbuEditErrmsg(p);
@@ -3591,10 +3896,26 @@
   return ((u32)aBuf[0] << 24)
        + ((u32)aBuf[1] << 16)
        + ((u32)aBuf[2] <<  8)
        + ((u32)aBuf[3]);
 }
+
+/*
+** Write an unsigned 32-bit value in big-endian format to the supplied
+** buffer.
+*/
+static void rbuPutU32(u8 *aBuf, u32 iVal){
+  aBuf[0] = (iVal >> 24) & 0xFF;
+  aBuf[1] = (iVal >> 16) & 0xFF;
+  aBuf[2] = (iVal >>  8) & 0xFF;
+  aBuf[3] = (iVal >>  0) & 0xFF;
+}
+
+static void rbuPutU16(u8 *aBuf, u16 iVal){
+  aBuf[0] = (iVal >>  8) & 0xFF;
+  aBuf[1] = (iVal >>  0) & 0xFF;
+}
 
 /*
 ** Read data from an rbuVfs-file.
 */
 static int rbuVfsRead(
@@ -3617,10 +3938,39 @@
     ){
       rc = SQLITE_OK;
       memset(zBuf, 0, iAmt);
     }else{
       rc = p->pReal->pMethods->xRead(p->pReal, zBuf, iAmt, iOfst);
+#if 1
+      /* If this is being called to read the first page of the target 
+      ** database as part of an rbu vacuum operation, synthesize the 
+      ** contents of the first page if it does not yet exist. Otherwise,
+      ** SQLite will not check for a *-wal file.  */
+      if( pRbu && rbuIsVacuum(pRbu) 
+          && rc==SQLITE_IOERR_SHORT_READ && iOfst==0
+          && (p->openFlags & SQLITE_OPEN_MAIN_DB)
+          && pRbu->rc==SQLITE_OK
+      ){
+        sqlite3_file *pFd = (sqlite3_file*)pRbu->pRbuFd;
+        rc = pFd->pMethods->xRead(pFd, zBuf, iAmt, iOfst);
+        if( rc==SQLITE_OK ){
+          u8 *aBuf = (u8*)zBuf;
+          u32 iRoot = rbuGetU32(&aBuf[52]) ? 1 : 0;
+          rbuPutU32(&aBuf[52], iRoot);      /* largest root page number */
+          rbuPutU32(&aBuf[36], 0);          /* number of free pages */
+          rbuPutU32(&aBuf[32], 0);          /* first page on free list trunk */
+          rbuPutU32(&aBuf[28], 1);          /* size of db file in pages */
+          rbuPutU32(&aBuf[24], pRbu->pRbuFd->iCookie+1);  /* Change counter */
+
+          if( iAmt>100 ){
+            memset(&aBuf[100], 0, iAmt-100);
+            rbuPutU16(&aBuf[105], iAmt & 0xFFFF);
+            aBuf[100] = 0x0D;
+          }
+        }
+      }
+#endif
     }
     if( rc==SQLITE_OK && iOfst==0 && (p->openFlags & SQLITE_OPEN_MAIN_DB) ){
       /* These look like magic numbers. But they are stable, as they are part
        ** of the definition of the SQLite file format, which may not change. */
       u8 *pBuf = (u8*)zBuf;
@@ -3691,11 +4041,24 @@
 /*
 ** Return the current file-size of an rbuVfs-file.
 */
 static int rbuVfsFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
   rbu_file *p = (rbu_file *)pFile;
-  return p->pReal->pMethods->xFileSize(p->pReal, pSize);
+  int rc;
+  rc = p->pReal->pMethods->xFileSize(p->pReal, pSize);
+
+  /* If this is an RBU vacuum operation and this is the target database,
+  ** pretend that it has at least one page. Otherwise, SQLite will not
+  ** check for the existance of a *-wal file. rbuVfsRead() contains 
+  ** similar logic.  */
+  if( rc==SQLITE_OK && *pSize==0 
+   && p->pRbu && rbuIsVacuum(p->pRbu) 
+   && (p->openFlags & SQLITE_OPEN_MAIN_DB)
+  ){
+    *pSize = 1024;
+  }
+  return rc;
 }
 
 /*
 ** Lock an rbuVfs-file.
 */
@@ -3703,11 +4066,13 @@
   rbu_file *p = (rbu_file*)pFile;
   sqlite3rbu *pRbu = p->pRbu;
   int rc = SQLITE_OK;
 
   assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
-  if( pRbu && eLock==SQLITE_LOCK_EXCLUSIVE && pRbu->eStage!=RBU_STAGE_DONE ){
+  if( eLock==SQLITE_LOCK_EXCLUSIVE 
+   && (p->bNolock || (pRbu && pRbu->eStage!=RBU_STAGE_DONE))
+  ){
     /* Do not allow EXCLUSIVE locks. Preventing SQLite from taking this 
     ** prevents it from checkpointing the database from sqlite3_close(). */
     rc = SQLITE_BUSY;
   }else{
     rc = p->pReal->pMethods->xLock(p->pReal, eLock);
@@ -3765,10 +4130,16 @@
         if( p->pWalFd ) p->pWalFd->pRbu = pRbu;
         rc = SQLITE_OK;
       }
     }
     return rc;
+  }
+  else if( op==SQLITE_FCNTL_RBUCNT ){
+    sqlite3rbu *pRbu = (sqlite3rbu*)pArg;
+    pRbu->nRbu++;
+    pRbu->pRbuFd = p;
+    p->bNolock = 1;
   }
 
   rc = xControl(p->pReal, op, pArg);
   if( rc==SQLITE_OK && op==SQLITE_FCNTL_VFSNAME ){
     rbu_vfs *pRbuVfs = p->pRbuVfs;
@@ -3928,10 +4299,37 @@
   sqlite3_mutex_enter(pRbuVfs->mutex);
   for(pDb=pRbuVfs->pMain; pDb && pDb->zWal!=zWal; pDb=pDb->pMainNext){}
   sqlite3_mutex_leave(pRbuVfs->mutex);
   return pDb;
 }
+
+/* 
+** A main database named zName has just been opened. The following 
+** function returns a pointer to a buffer owned by SQLite that contains
+** the name of the *-wal file this db connection will use. SQLite
+** happens to pass a pointer to this buffer when using xAccess()
+** or xOpen() to operate on the *-wal file.  
+*/
+static const char *rbuMainToWal(const char *zName, int flags){
+  int n = (int)strlen(zName);
+  const char *z = &zName[n];
+  if( flags & SQLITE_OPEN_URI ){
+    int odd = 0;
+    while( 1 ){
+      if( z[0]==0 ){
+        odd = 1 - odd;
+        if( odd && z[1]==0 ) break;
+      }
+      z++;
+    }
+    z += 2;
+  }else{
+    while( *z==0 ) z++;
+  }
+  z += (n + 8 + 1);
+  return z;
+}
 
 /*
 ** Open an rbu file handle.
 */
 static int rbuVfsOpen(
@@ -3964,10 +4362,11 @@
   rbu_vfs *pRbuVfs = (rbu_vfs*)pVfs;
   sqlite3_vfs *pRealVfs = pRbuVfs->pRealVfs;
   rbu_file *pFd = (rbu_file *)pFile;
   int rc = SQLITE_OK;
   const char *zOpen = zName;
+  int oflags = flags;
 
   memset(pFd, 0, sizeof(rbu_file));
   pFd->pReal = (sqlite3_file*)&pFd[1];
   pFd->pRbuVfs = pRbuVfs;
   pFd->openFlags = flags;
@@ -3976,40 +4375,31 @@
       /* A main database has just been opened. The following block sets
       ** (pFd->zWal) to point to a buffer owned by SQLite that contains
       ** the name of the *-wal file this db connection will use. SQLite
       ** happens to pass a pointer to this buffer when using xAccess()
       ** or xOpen() to operate on the *-wal file.  */
-      int n = (int)strlen(zName);
-      const char *z = &zName[n];
-      if( flags & SQLITE_OPEN_URI ){
-        int odd = 0;
-        while( 1 ){
-          if( z[0]==0 ){
-            odd = 1 - odd;
-            if( odd && z[1]==0 ) break;
-          }
-          z++;
-        }
-        z += 2;
-      }else{
-        while( *z==0 ) z++;
-      }
-      z += (n + 8 + 1);
-      pFd->zWal = z;
+      pFd->zWal = rbuMainToWal(zName, flags);
     }
     else if( flags & SQLITE_OPEN_WAL ){
       rbu_file *pDb = rbuFindMaindb(pRbuVfs, zName);
       if( pDb ){
         if( pDb->pRbu && pDb->pRbu->eStage==RBU_STAGE_OAL ){
           /* This call is to open a *-wal file. Intead, open the *-oal. This
           ** code ensures that the string passed to xOpen() is terminated by a
           ** pair of '\0' bytes in case the VFS attempts to extract a URI 
           ** parameter from it.  */
-          size_t nCopy = strlen(zName);
-          char *zCopy = sqlite3_malloc64(nCopy+2);
+          const char *zBase = zName;
+          size_t nCopy;
+          char *zCopy;
+          if( rbuIsVacuum(pDb->pRbu) ){
+            zBase = sqlite3_db_filename(pDb->pRbu->dbRbu, "main");
+            zBase = rbuMainToWal(zBase, SQLITE_OPEN_URI);
+          }
+          nCopy = strlen(zBase);
+          zCopy = sqlite3_malloc64(nCopy+2);
           if( zCopy ){
-            memcpy(zCopy, zName, nCopy);
+            memcpy(zCopy, zBase, nCopy);
             zCopy[nCopy-3] = 'o';
             zCopy[nCopy] = '\0';
             zCopy[nCopy+1] = '\0';
             zOpen = (const char*)(pFd->zDel = zCopy);
           }else{
@@ -4019,13 +4409,22 @@
         }
         pDb->pWalFd = pFd;
       }
     }
   }
+
+  if( oflags & SQLITE_OPEN_MAIN_DB 
+   && sqlite3_uri_boolean(zName, "rbu_memory", 0) 
+  ){
+    assert( oflags & SQLITE_OPEN_MAIN_DB );
+    oflags =  SQLITE_OPEN_TEMP_DB | SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
+              SQLITE_OPEN_EXCLUSIVE | SQLITE_OPEN_DELETEONCLOSE;
+    zOpen = 0;
+  }
 
   if( rc==SQLITE_OK ){
-    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, flags, pOutFlags);
+    rc = pRealVfs->xOpen(pRealVfs, zOpen, pFd->pReal, oflags, pOutFlags);
   }
   if( pFd->pReal->pMethods ){
     /* The xOpen() operation has succeeded. Set the sqlite3_file.pMethods
     ** pointer and, if the file is a main database file, link it into the
     ** mutex protected linked list of all such files.  */

Index: ext/rbu/sqlite3rbu.h
==================================================================
--- ext/rbu/sqlite3rbu.h
+++ ext/rbu/sqlite3rbu.h
@@ -311,10 +311,42 @@
 sqlite3rbu *sqlite3rbu_open(
   const char *zTarget, 
   const char *zRbu,
   const char *zState
 );
+
+/*
+** Open an RBU handle to perform an RBU vacuum on database file zTarget.
+** An RBU vacuum is similar to SQLite's built-in VACUUM command, except
+** that it can be suspended and resumed like an RBU update.
+**
+** The second argument to this function, which may not be NULL, identifies 
+** a database in which to store the state of the RBU vacuum operation if
+** it is suspended. The first time sqlite3rbu_vacuum() is called, to start
+** an RBU vacuum operation, the state database should either not exist or
+** be empty (contain no tables). If an RBU vacuum is suspended by calling
+** sqlite3rbu_close() on the RBU handle before sqlite3rbu_step() has
+** returned SQLITE_DONE, the vacuum state is stored in the state database. 
+** The vacuum can be resumed by calling this function to open a new RBU
+** handle specifying the same target and state databases.
+**
+** This function does not delete the state database after an RBU vacuum
+** is completed, even if it created it. However, if the call to
+** sqlite3rbu_close() returns any value other than SQLITE_OK, the contents
+** of the state tables within the state database are zeroed. This way,
+** the next call to sqlite3rbu_vacuum() opens a handle that starts a 
+** new RBU vacuum operation.
+**
+** As with sqlite3rbu_open(), Zipvfs users should rever to the comment
+** describing the sqlite3rbu_create_vfs() API function below for 
+** a description of the complications associated with using RBU with 
+** zipvfs databases.
+*/
+sqlite3rbu *sqlite3rbu_vacuum(
+  const char *zTarget, 
+  const char *zState
+);
 
 /*
 ** Internally, each RBU connection uses a separate SQLite database 
 ** connection to access the target and rbu update databases. This
 ** API allows the application direct access to these database handles.

Index: ext/rbu/test_rbu.c
==================================================================
--- ext/rbu/test_rbu.c
+++ ext/rbu/test_rbu.c
@@ -184,10 +184,38 @@
   pRbu = sqlite3rbu_open(zTarget, zRbu, zStateDb);
   Tcl_CreateObjCommand(interp, zCmd, test_sqlite3rbu_cmd, (ClientData)pRbu, 0);
   Tcl_SetObjResult(interp, objv[1]);
   return TCL_OK;
 }
+
+/*
+** Tclcmd: sqlite3rbu_vacuum CMD <target-db> <state-db>
+*/
+static int test_sqlite3rbu_vacuum(
+  ClientData clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  sqlite3rbu *pRbu = 0;
+  const char *zCmd;
+  const char *zTarget;
+  const char *zStateDb = 0;
+
+  if( objc!=4 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "NAME TARGET-DB STATE-DB");
+    return TCL_ERROR;
+  }
+  zCmd = Tcl_GetString(objv[1]);
+  zTarget = Tcl_GetString(objv[2]);
+  zStateDb = Tcl_GetString(objv[3]);
+
+  pRbu = sqlite3rbu_vacuum(zTarget, zStateDb);
+  Tcl_CreateObjCommand(interp, zCmd, test_sqlite3rbu_cmd, (ClientData)pRbu, 0);
+  Tcl_SetObjResult(interp, objv[1]);
+  return TCL_OK;
+}
 
 /*
 ** Tclcmd: sqlite3rbu_create_vfs ?-default? NAME PARENT
 */
 static int test_sqlite3rbu_create_vfs(
@@ -272,10 +300,11 @@
   static struct {
      char *zName;
      Tcl_ObjCmdProc *xProc;
   } aObjCmd[] = {
     { "sqlite3rbu", test_sqlite3rbu },
+    { "sqlite3rbu_vacuum", test_sqlite3rbu_vacuum },
     { "sqlite3rbu_create_vfs", test_sqlite3rbu_create_vfs },
     { "sqlite3rbu_destroy_vfs", test_sqlite3rbu_destroy_vfs },
     { "sqlite3rbu_internal_test", test_sqlite3rbu_internal_test },
   };
   int i;

Index: src/expr.c
==================================================================
--- src/expr.c
+++ src/expr.c
@@ -2358,11 +2358,11 @@
     }
     p->tempReg = 0;
   }
   p->iReg = 0;
   pParse->nColCache--;
-  assert( cacheIsValid(pParse) );
+  assert( pParse->db->mallocFailed || cacheIsValid(pParse) );
 }
 
 
 /*
 ** Record in the column cache that a particular column from a
@@ -2403,11 +2403,11 @@
       p->iColumn = iCol;
       p->iReg = iReg;
       p->tempReg = 0;
       p->lru = pParse->iCacheCnt++;
       pParse->nColCache++;
-      assert( cacheIsValid(pParse) );
+      assert( pParse->db->mallocFailed || cacheIsValid(pParse) );
       return;
     }
   }
 
   /* Replace the last recently used */