Index: src/pager.c
==================================================================
--- src/pager.c
+++ src/pager.c
@@ -4230,11 +4230,11 @@
 **
 ** SQLITE_OK is returned if successful, or an error code if an error occurs.
 */
 int sqlite3PagerSetFilesize(Pager *pPager, i64 szReq){
   int rc;
-  sqlite3_int64 sz;
+  i64 sz;                         /* Size of file on disk in bytes */
 
   assert( pPager->eState==PAGER_OPEN );
   assert( pPager->nMmapOut==0 );
 
   rc = sqlite3OsFileSize(pPager->fd, &sz);
@@ -4242,17 +4242,17 @@
     if( sz>szReq ){
       sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_SIZE_HINT, &sz);
     }
   }
 
-  if( rc==SQLITE_OK 
-   && pPager->nMapLimit>0 
-   && pPager->nMapValid<szReq 
-   && pPager->nMapValid<pPager->nMapLimit 
-  ){
-    pPager->dbFileSize = (szReq / pPager->pageSize);
-    rc = pagerMap(pPager, 1);
+
+  if( rc==SQLITE_OK ){
+    i64 szMap = (szReq > pPager->nMapLimit) ? pPager->nMapLimit : szReq;
+    if( pPager->nMapValid!=pPager->nMap || szMap!=pPager->nMap ){
+      pPager->dbFileSize = (szReq / pPager->pageSize);
+      rc = pagerMap(pPager, 1);
+    }
   }
 
   return rc;
 }
 

Index: test/mmap1.test
==================================================================
--- test/mmap1.test
+++ test/mmap1.test
@@ -21,17 +21,21 @@
   array set stats [btree_pager_stats $bt]
   db_leave $db
   return $stats(read)
 }
 
-foreach {t mmap_size nRead} {
-  1 { PRAGMA mmap_size = -65536 }   4
-  2 { PRAGMA mmap_size = -50    } 156
-  3 { PRAGMA mmap_size = 0      } 344
+foreach {t mmap_size nRead c2init} {
+  1.1 { PRAGMA mmap_size = -65536 }   4 {}
+  1.2 { PRAGMA mmap_size = -50    } 156 {}
+  1.3 { PRAGMA mmap_size = 0      } 344 {}
+  1.4 { PRAGMA mmap_size = -65536 }   4 {PRAGMA mmap_size = -65536}
+  1.5 { PRAGMA mmap_size = -50    } 156 {PRAGMA mmap_size = -65536}
+  1.6 { PRAGMA mmap_size = 0      } 344 {PRAGMA mmap_size = -65536}
 } {
   do_multiclient_test tn {
     sql1 $mmap_size
+    sql2 $c2init
 
     code2 {
       set ::rcnt 0
       proc rblob {n} {
         set ::rcnt [expr (($::rcnt << 3) + $::rcnt + 456) & 0xFFFFFFFF]
@@ -77,8 +81,53 @@
     # "PRAGMA mmap_size" command worked.
     do_test $t.$tn.5 { nRead db } $nRead
   }
 }
 
+set ::rcnt 0
+proc rblob {n} {
+  set ::rcnt [expr (($::rcnt << 3) + $::rcnt + 456) & 0xFFFFFFFF]
+  set str [format %.8x [expr $::rcnt ^ 0xbdf20da3]] 
+  string range [string repeat $str [expr $n/4]] 1 $n
+}
+
+reset_db
+db func rblob rblob
+
+do_execsql_test 2.1 {
+  PRAGMA auto_vacuum = 1;
+  PRAGMA mmap_size = -65536;
+  PRAGMA journal_mode = wal;
+  CREATE TABLE t1(a, b, UNIQUE(a, b));
+  INSERT INTO t1 VALUES(rblob(500), rblob(500));
+  INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --    2
+  INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --    4
+  INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --    8
+  INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --   16
+  INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --   32
+  PRAGMA wal_checkpoint;
+} {wal 0 103 103}
+
+do_execsql_test 2.2 {
+  PRAGMA auto_vacuum;
+  SELECT count(*) FROM t1;
+} {1 32}
+
+do_test 2.3 {
+  sqlite3 db2 test.db
+  db2 func rblob rblob
+  db2 eval { 
+    DELETE FROM t1 WHERE (rowid%4);
+    PRAGMA wal_checkpoint;
+  }
+  db2 eval { 
+    INSERT INTO t1 SELECT rblob(500), rblob(500) FROM t1; --    16
+    SELECT count(*) FROM t1;
+  }
+} {16}
+
+do_execsql_test 2.4 {
+  PRAGMA wal_checkpoint;
+} {0 24 24}
 
 finish_test
 

Index: test/speed1p.test
==================================================================
--- test/speed1p.test
+++ test/speed1p.test
@@ -63,13 +63,10 @@
 
 # Create a database schema.
 #
 do_test speed1p-1.0 {
   execsql {
-    PRAGMA mmap_size=65536;
-    PRAGMA journal_mode=wal;
-
     PRAGMA page_size=1024;
     PRAGMA cache_size=500;
     PRAGMA locking_mode=EXCLUSIVE;
     CREATE TABLE t1(a INTEGER, b INTEGER, c TEXT);
     CREATE TABLE t2(a INTEGER, b INTEGER, c TEXT);