Index: src/os_unix.c
==================================================================
--- src/os_unix.c
+++ src/os_unix.c
@@ -44,10 +44,17 @@
 **      plus implementations of sqlite3_os_init() and sqlite3_os_end().
 */
 #include "sqliteInt.h"
 #if SQLITE_OS_UNIX              /* This file is used on unix only */
 
+/* Use posix_fallocate() if it is available
+*/
+#if !defined(HAVE_POSIX_FALLOCATE) \
+      && (_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L)
+# define HAVE_POSIX_FALLOCATE 1
+#endif
+
 /*
 ** There are various methods for file locking used for concurrency
 ** control:
 **
 **   1. POSIX locking (the default),
@@ -4166,15 +4173,23 @@
         **
         ** Alternatively, if bExtend is true, use ftruncate() to allocate
         ** the requested memory region.
         */
         if( !bExtend ) goto shmpage_out;
+#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
+        if( osFallocate(pShmNode->h, sStat.st_size, nByte)!=0 ){
+          rc = unixLogError(SQLITE_IOERR_SHMSIZE, "fallocate",
+                            pShmNode->zFilename);
+          goto shmpage_out;
+        }
+#else
         if( robust_ftruncate(pShmNode->h, nByte) ){
           rc = unixLogError(SQLITE_IOERR_SHMSIZE, "ftruncate",
                             pShmNode->zFilename);
           goto shmpage_out;
         }
+#endif
       }
     }
 
     /* Map the requested memory region into this processes address space. */
     apNew = (char **)sqlite3_realloc(

Index: test/wal9.test
==================================================================
--- test/wal9.test
+++ test/wal9.test
@@ -60,11 +60,11 @@
 
 # Check file sizes are as expected. The real requirement here is that 
 # the *shm file is now more than one chunk (>32KiB).
 do_test 1.3 { file size test.db     } {1024}
 do_test 1.4 { file size test.db-wal } {15421352}
-do_test 1.5 { file size test.db-shm } {131072}
+do_test 1.5 { expr {[file size test.db-shm]>32768} } {1}
 
 do_execsql_test 1.6 { PRAGMA wal_checkpoint } {0 14715 14715}
 
 # At this point connection [db2] has mapped the first 32KB of the *shm file
 # only. Because the entire WAL file has been checkpointed, it is not 
@@ -85,6 +85,5 @@
   } db2
 } {}
 db2 close
 
 finish_test
-