Index: src/test_multiplex.c
==================================================================
--- src/test_multiplex.c
+++ src/test_multiplex.c
@@ -1000,10 +1000,30 @@
     case SQLITE_FCNTL_SIZE_HINT:
     case SQLITE_FCNTL_CHUNK_SIZE:
       /* no-op these */
       rc = SQLITE_OK;
       break;
+    case SQLITE_FCNTL_PRAGMA: {
+      char **aFcntl = (char**)pArg;
+      if( aFcntl[1] && sqlite3_stricmp(aFcntl[1],"multiplex_truncate")==0 ){
+        if( aFcntl[2] && aFcntl[2][0] ){
+          if( sqlite3_stricmp(aFcntl[2], "on")==0
+           || sqlite3_stricmp(aFcntl[2], "1")==0 ){
+            pGroup->bTruncate = 1;
+          }else
+          if( sqlite3_stricmp(aFcntl[2], "off")==0
+           || sqlite3_stricmp(aFcntl[2], "0")==0 ){
+            pGroup->bTruncate = 0;
+          }
+        }
+        aFcntl[0] = sqlite3_mprintf(pGroup->bTruncate ? "on" : "off");
+        rc = SQLITE_OK;
+        break;
+      }
+      /* If the multiplexor does not handle the pragma, pass it through
+      ** into the default case. */
+    }
     default:
       pSubOpen = multiplexSubOpen(pGroup, 0, &rc, NULL, 0);
       if( pSubOpen ){
         rc = pSubOpen->pMethods->xFileControl(pSubOpen, op, pArg);
         if( op==SQLITE_FCNTL_VFSNAME && rc==SQLITE_OK ){

ADDED   test/multiplex4.test
Index: test/multiplex4.test
==================================================================
--- /dev/null
+++ test/multiplex4.test
@@ -0,0 +1,114 @@
+# 2014-09-25
+#
+# 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 "truncate" option in the multiplexor.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set ::testprefix multiplex4
+
+db close
+sqlite3_shutdown
+sqlite3_multiplex_initialize {} 0
+
+# delete all filesl with the base name of $basename
+#
+proc multiplex_delete_db {basename} {
+  foreach file [glob -nocomplain $basename.*] {
+    forcedelete $file
+  }
+}
+
+# Return a sorted list of all files with the base name of $basename.
+# Except, delete all text from the end of $basename through the NNN
+# suffix on the end of the filename.
+#
+proc multiplex_file_list {basename} {
+  set x {}
+  foreach file [glob -nocomplain $basename.*] {
+    regsub "^$basename\\..*(\\d\\d\\d)\$" $file $basename.\\1 file
+    lappend x $file
+  }
+  return [lsort $x]
+}
+
+do_test multiplex4-1.0 {
+  multiplex_delete_db mx4test
+  sqlite3 db {file:mx4test.db?chunksize=10&truncate=1} -uri 1 -vfs multiplex
+  db eval {
+    CREATE TABLE t1(x);
+    INSERT INTO t1(x) VALUES(randomblob(250000));
+  }
+  multiplex_file_list mx4test
+} {mx4test.001 mx4test.db}
+
+do_test multiplex4-1.1 {
+  db eval {
+    DELETE FROM t1;
+    VACUUM;
+  }
+  multiplex_file_list mx4test
+} {mx4test.db}
+
+do_test multiplex4-1.2 {
+  db eval {PRAGMA multiplex_truncate}
+} {on}
+do_test multiplex4-1.3 {
+  db eval {PRAGMA multiplex_truncate=off}
+} {off}
+do_test multiplex4-1.4 {
+  db eval {PRAGMA multiplex_truncate}
+} {off}
+do_test multiplex4-1.5 {
+  db eval {PRAGMA multiplex_truncate=on}
+} {on}
+do_test multiplex4-1.6 {
+  db eval {PRAGMA multiplex_truncate}
+} {on}
+do_test multiplex4-1.7 {
+  db eval {PRAGMA multiplex_truncate=0}
+} {off}
+do_test multiplex4-1.8 {
+  db eval {PRAGMA multiplex_truncate=1}
+} {on}
+do_test multiplex4-1.9 {
+  db eval {PRAGMA multiplex_truncate=0}
+} {off}
+
+do_test multiplex4-1.10 {
+  db eval {
+    INSERT INTO t1(x) VALUES(randomblob(250000));
+  }
+  multiplex_file_list mx4test
+} {mx4test.001 mx4test.db}
+
+do_test multiplex4-1.11 {
+  db eval {
+    DELETE FROM t1;
+    VACUUM;
+  }
+  multiplex_file_list mx4test
+} {mx4test.001 mx4test.db}
+
+do_test multiplex4-1.12 {
+  db eval {
+    PRAGMA multiplex_truncate=ON;
+    DROP TABLE t1;
+    VACUUM;
+  }
+  multiplex_file_list mx4test
+} {mx4test.db}
+
+catch { db close }
+forcedelete mx4test.db
+sqlite3_multiplex_shutdown
+finish_test