Index: ext/ota/ota.c
==================================================================
--- ext/ota/ota.c
+++ ext/ota/ota.c
@@ -39,10 +39,15 @@
 "  target db.\n"
 "\n"
 , zArgv0);
   exit(1);
 }
+
+void report_default_vfs(){
+  sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
+  fprintf(stdout, "using vfs \"%s\"\n", pVfs->zName);
+}
 
 int main(int argc, char **argv){
   int i;
   const char *zTarget;            /* Target database to apply OTA to */
   const char *zOta;               /* Database containing OTA */
@@ -60,10 +65,12 @@
   }else if( argc!=3 ){
     usage(argv[0]);
   }
   zTarget = argv[argc-2];
   zOta = argv[argc-1];
+
+  report_default_vfs();
 
   /* Open an OTA handle. If nStep is less than or equal to zero, call
   ** sqlite3ota_step() until either the OTA has been completely applied
   ** or an error occurs. Or, if nStep is greater than zero, call
   ** sqlite3ota_step() a maximum of nStep times.  */

Index: src/vdbesort.c
==================================================================
--- src/vdbesort.c
+++ src/vdbesort.c
@@ -599,11 +599,13 @@
 ** Or, if an error occurs, return an SQLite error code. The final value of
 ** *pp is undefined in this case.
 */
 static int vdbeSorterMapFile(SortSubtask *pTask, SorterFile *pFile, u8 **pp){
   int rc = SQLITE_OK;
-  if( pFile->iEof<=(i64)(pTask->pSorter->db->nMaxSorterMmap) ){
+  if( pFile->iEof<=(i64)(pTask->pSorter->db->nMaxSorterMmap)
+   && pFile->pFd->pMethods->xFetch 
+  ){
     rc = sqlite3OsFetch(pFile->pFd, 0, (int)pFile->iEof, (void**)pp);
     testcase( rc!=SQLITE_OK );
   }
   return rc;
 }
@@ -1121,11 +1123,11 @@
 ** the specific VFS implementation.
 */
 static void vdbeSorterExtendFile(sqlite3 *db, sqlite3_file *pFd, i64 nByte){
   if( nByte<=(i64)(db->nMaxSorterMmap) ){
     int rc = sqlite3OsTruncate(pFd, nByte);
-    if( rc==SQLITE_OK ){
+    if( rc==SQLITE_OK && pFd->pMethods->xFetch ){
       void *p = 0;
       sqlite3OsFetch(pFd, 0, (int)nByte, &p);
       sqlite3OsUnfetch(pFd, 0, p);
     }
   }