Index: ext/rbu/rbu1.test
==================================================================
--- ext/rbu/rbu1.test
+++ ext/rbu/rbu1.test
@@ -8,14 +8,11 @@
 #    May you share freely, never taking more than you give.
 #
 #***********************************************************************
 #
 
-if {![info exists testdir]} {
-  set testdir [file join [file dirname [info script]] .. .. test]
-}
-source $testdir/tester.tcl
+source [file join [file dirname [info script]] rbu_common.tcl]
 set ::testprefix rbu1
 
 db close
 sqlite3_shutdown
 sqlite3_config_uri 1
@@ -94,30 +91,10 @@
   }
   rbu5 close
   return $filename
 }
 
-# Run the RBU in file $rbu on target database $target until completion.
-#
-proc run_rbu {target rbu} {
-  sqlite3rbu rbu $target $rbu
-  while 1 {
-    set rc [rbu step]
-    if {$rc!="SQLITE_OK"} break
-  }
-  rbu close
-}
-
-proc step_rbu {target rbu} {
-  while 1 {
-    sqlite3rbu rbu $target $rbu
-    set rc [rbu step]
-    rbu close
-    if {$rc != "SQLITE_OK"} break
-  }
-  set rc
-}
 
 # Same as [step_rbu], except using a URI to open the target db.
 #
 proc step_rbu_uri {target rbu} {
   while 1 {
@@ -639,14 +616,29 @@
 
   # Test that an RBU database containing no input tables is handled
   # correctly.
   reset_db
   forcedelete rbu.db
-  do_test $tn3.8 {
+  do_test $tn3.8.1 {
+    list [catch { run_rbu test.db rbu.db } msg] $msg
+  } {0 SQLITE_DONE}
+
+  # Test that an RBU database containing only empty data_xxx tables is
+  # also handled correctly.
+  reset_db
+  forcedelete rbu.db
+  do_execsql_test $tn3.8.2.1 {
+    CREATE TABLE t1(a PRIMARY KEY, b);
+    INSERT INTO t1 VALUES(1, 2);
+    ATTACH 'rbu.db' AS rbu;
+    CREATE TABLE data_t1(a, b, rbu_control);
+    DETACH rbu;
+  }
+  do_test $tn3.8.2.1 {
     list [catch { run_rbu test.db rbu.db } msg] $msg
   } {0 SQLITE_DONE}
-  
+
   # Test that RBU can update indexes containing NULL values.
   #
   reset_db
   forcedelete rbu.db
   do_execsql_test $tn3.9.1 {

Index: ext/rbu/rbu5.test
==================================================================
--- ext/rbu/rbu5.test
+++ ext/rbu/rbu5.test
@@ -10,39 +10,14 @@
 #***********************************************************************
 #
 # Test some properties of the pager_rbu_mode and rbu_mode pragmas.
 #
 
-if {![info exists testdir]} {
-  set testdir [file join [file dirname [info script]] .. .. test]
-}
-source $testdir/tester.tcl
+source [file join [file dirname [info script]] rbu_common.tcl]
 set ::testprefix rbu5
 
 
-# Run the RBU in file $rbu on target database $target until completion.
-#
-proc run_rbu {target rbu} {
-  sqlite3rbu rbu $target $rbu
-  while { [rbu step]=="SQLITE_OK" } {}
-  rbu close
-}
-
-
-# Run the RBU in file $rbu on target database $target one step at a
-# time until completion.
-#
-proc step_rbu {target rbu} {
-  while 1 {
-    sqlite3rbu rbu $target $rbu
-    set rc [rbu step]
-    rbu close
-    if {$rc != "SQLITE_OK"} break
-  }
-  set rc
-}
-
 # Return a list of the primary key columns for table $tbl in the database
 # opened by database handle $db.
 #
 proc pkcols {db tbl} {
   set ret [list]

Index: ext/rbu/rbu_common.tcl
==================================================================
--- ext/rbu/rbu_common.tcl
+++ ext/rbu/rbu_common.tcl
@@ -12,26 +12,60 @@
 
 if {![info exists testdir]} {
   set testdir [file join [file dirname [info script]] .. .. test]
 }
 source $testdir/tester.tcl
+
+proc check_prestep_state {target state} {
+  set oal_exists [file exists $target-oal]
+  set wal_exists [file exists $target-wal]
+  set progress [rbu progress]
+
+  if {($progress==0 && $state!="oal" && $state!="done")
+   || ($oal_exists && $wal_exists)
+   || ($progress>0 && $state=="oal" && (!$oal_exists || $wal_exists))
+   || ($state=="move" && (!$oal_exists || $wal_exists))
+   || ($state=="checkpoint" && ($oal_exists || !$wal_exists))
+   || ($state=="done" && ($oal_exists && $progress!=0))
+  } {
+    error "B: state=$state progress=$progress oal=$oal_exists wal=$wal_exists"
+  }
+}
+
+proc check_poststep_state {rc target state} {
+  if {$rc=="SQLITE_OK" || $rc=="SQLITE_DONE"} {
+    set oal_exists [file exists $target-oal]
+    set wal_exists [file exists $target-wal]
+    if {$state=="move" && ($oal_exists || !$wal_exists)} {
+      error "A: state=$state progress=$progress oal=$oal_exists wal=$wal_exists"
+    }
+  }
+}
 
 # Run the RBU in file $rbu on target database $target until completion.
 #
 proc run_rbu {target rbu} {
   sqlite3rbu rbu $target $rbu
   while 1 {
+    set state [rbu state]
+
+    check_prestep_state $target $state
     set rc [rbu step]
+    check_poststep_state $rc $target $state
+
     if {$rc!="SQLITE_OK"} break
   }
   rbu close
 }
 
 proc step_rbu {target rbu} {
   while 1 {
     sqlite3rbu rbu $target $rbu
+    set state [rbu state]
+    check_prestep_state $target $state
     set rc [rbu step]
+    check_poststep_state $rc $target $state
     rbu close
     if {$rc != "SQLITE_OK"} break
   }
   set rc
 }
@@ -39,11 +73,14 @@
 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 state [rbu state]
+      check_prestep_state test.db $state
       set rc [rbu step]
+      check_poststep_state $rc test.db $state
       if {$rc!="SQLITE_OK"} break
       if {$step==1} { rbu close }
     }
     rbu close
   } {SQLITE_DONE}]

Index: ext/rbu/sqlite3rbu.c
==================================================================
--- ext/rbu/sqlite3rbu.c
+++ ext/rbu/sqlite3rbu.c
@@ -3553,34 +3553,11 @@
     }
 
     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. */
-        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", 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.  */
-        if( p->rc==SQLITE_OK ){
-          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);
-          }
-        }
+        p->rc = sqlite3_exec(p->dbRbu, "BEGIN", 0, 0, &p->zErrmsg);
 
         /* Point the object iterator at the first object */
         if( p->rc==SQLITE_OK ){
           p->rc = rbuObjIterFirst(p, &p->objiter);
         }
@@ -3587,16 +3564,38 @@
 
         /* If the RBU database contains no data_xxx tables, declare the RBU
         ** update finished.  */
         if( p->rc==SQLITE_OK && p->objiter.zTbl==0 ){
           p->rc = SQLITE_DONE;
+          p->eStage = RBU_STAGE_DONE;
+        }else{
+          if( p->rc==SQLITE_OK && 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. */
+          if( p->rc==SQLITE_OK ){
+            p->rc = sqlite3_exec(db, "BEGIN IMMEDIATE", 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.  */
+          if( p->rc==SQLITE_OK ){
+            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( p->rc==SQLITE_OK ){
+            rbuSetupOal(p, pState);
+          }
         }
-
-        if( p->rc==SQLITE_OK ){
-          rbuSetupOal(p, pState);
-        }
-
       }else if( p->eStage==RBU_STAGE_MOVE ){
         /* no-op */
       }else if( p->eStage==RBU_STAGE_CKPT ){
         rbuSetupCheckpoint(p, pState);
       }else if( p->eStage==RBU_STAGE_DONE ){
@@ -3758,14 +3757,44 @@
 
     default:
       assert( 0 );
   }
 }
+
+/*
+** Return the current state of the RBU vacuum or update operation.
+*/
+int sqlite3rbu_state(sqlite3rbu *p){
+  int aRes[] = {
+    0, SQLITE_RBU_STATE_OAL, SQLITE_RBU_STATE_MOVE,
+    0, SQLITE_RBU_STATE_CHECKPOINT, SQLITE_RBU_STATE_DONE
+  };
+
+  assert( RBU_STAGE_OAL==1 );
+  assert( RBU_STAGE_MOVE==2 );
+  assert( RBU_STAGE_CKPT==4 );
+  assert( RBU_STAGE_DONE==5 );
+  assert( aRes[RBU_STAGE_OAL]==SQLITE_RBU_STATE_OAL );
+  assert( aRes[RBU_STAGE_MOVE]==SQLITE_RBU_STATE_MOVE );
+  assert( aRes[RBU_STAGE_CKPT]==SQLITE_RBU_STATE_CHECKPOINT );
+  assert( aRes[RBU_STAGE_DONE]==SQLITE_RBU_STATE_DONE );
+
+  if( p->rc!=SQLITE_OK && p->rc!=SQLITE_DONE ){
+    return SQLITE_RBU_STATE_ERROR;
+  }else{
+    assert( p->rc!=SQLITE_DONE || p->eStage==RBU_STAGE_DONE );
+    assert( p->eStage==RBU_STAGE_OAL
+         || p->eStage==RBU_STAGE_MOVE
+         || p->eStage==RBU_STAGE_CKPT
+         || p->eStage==RBU_STAGE_DONE
+    );
+    return aRes[p->eStage];
+  }
+}
 
 int sqlite3rbu_savestate(sqlite3rbu *p){
   int rc = p->rc;
-  
   if( rc==SQLITE_DONE ) return SQLITE_OK;
 
   assert( p->eStage>=RBU_STAGE_OAL && p->eStage<=RBU_STAGE_DONE );
   if( p->eStage==RBU_STAGE_OAL ){
     assert( rc!=SQLITE_DONE );

Index: ext/rbu/sqlite3rbu.h
==================================================================
--- ext/rbu/sqlite3rbu.h
+++ ext/rbu/sqlite3rbu.h
@@ -472,10 +472,48 @@
 ** table exists but is not correctly populated, the value of the *pnOne
 ** output variable during stage 1 is undefined.
 */
 void sqlite3rbu_bp_progress(sqlite3rbu *pRbu, int *pnOne, int *pnTwo);
 
+/*
+** Obtain an indication as to the current stage of an RBU update or vacuum.
+** This function always returns one of the SQLITE_RBU_STATE_XXX constants
+** defined in this file. Return values should be interpreted as follows:
+**
+** SQLITE_RBU_STATE_OAL:
+**   RBU is currently building a *-oal file. The next call to sqlite3rbu_step()
+**   may either add further data to the *-oal file, or compute data that will
+**   be added by a subsequent call.
+**
+** SQLITE_RBU_STATE_MOVE:
+**   RBU has finished building the *-oal file. The next call to sqlite3rbu_step()
+**   will move the *-oal file to the equivalent *-wal path. If the current
+**   operation is an RBU update, then the updated version of the database
+**   file will become visible to ordinary SQLite clients following the next
+**   call to sqlite3rbu_step().
+**
+** SQLITE_RBU_STATE_CHECKPOINT:
+**   RBU is currently performing an incremental checkpoint. The next call to
+**   sqlite3rbu_step() will copy a page of data from the *-wal file into
+**   the target database file.
+**
+** SQLITE_RBU_STATE_DONE:
+**   The RBU operation has finished. Any subsequent calls to sqlite3rbu_step()
+**   will immediately return SQLITE_DONE.
+**
+** SQLITE_RBU_STATE_ERROR:
+**   An error has occurred. Any subsequent calls to sqlite3rbu_step() will
+**   immediately return the SQLite error code associated with the error.
+*/
+#define SQLITE_RBU_STATE_OAL        1
+#define SQLITE_RBU_STATE_MOVE       2
+#define SQLITE_RBU_STATE_CHECKPOINT 3
+#define SQLITE_RBU_STATE_DONE       4
+#define SQLITE_RBU_STATE_ERROR      5
+
+int sqlite3rbu_state(sqlite3rbu *pRbu);
+
 /*
 ** Create an RBU VFS named zName that accesses the underlying file-system
 ** via existing VFS zParent. Or, if the zParent parameter is passed NULL, 
 ** then the new RBU VFS uses the default system VFS to access the file-system.
 ** The new object is registered as a non-default VFS with SQLite before 

Index: ext/rbu/test_rbu.c
==================================================================
--- ext/rbu/test_rbu.c
+++ ext/rbu/test_rbu.c
@@ -67,10 +67,12 @@
     {"create_rbu_delta", 2, ""},  /* 2 */
     {"savestate", 2, ""},         /* 3 */
     {"dbMain_eval", 3, "SQL"},    /* 4 */
     {"bp_progress", 2, ""},       /* 5 */
     {"db", 3, "RBU"},             /* 6 */
+    {"state", 2, ""},             /* 7 */
+    {"progress", 2, ""},          /* 8 */
     {0,0,0}
   };
   int iCmd;
 
   if( objc<2 ){
@@ -163,10 +165,22 @@
         }else{
           Tcl_SetResult(interp, zBuf, TCL_VOLATILE);
         }
       }
       break;
+    }
+    case 7: /* state */ {
+      const char *aRes[] = { 0, "oal", "move", "checkpoint", "done", "error" };
+      int eState = sqlite3rbu_state(pRbu);
+      assert( eState>0 && eState<=5 );
+      Tcl_SetResult(interp, (char*)aRes[eState], TCL_STATIC);
+      break;
+    }
+    case 8: /* progress */ {
+      sqlite3_int64 nStep =  sqlite3rbu_progress(pRbu);
+      Tcl_SetObjResult(interp, Tcl_NewWideIntObj(nStep));
+      break;
     }
 
     default: /* seems unlikely */
       assert( !"cannot happen" );
       break;