diff --git a/manifest b/manifest
index a61f43717c..97b08ff77e 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Use\smmap()\sto\sread\sfrom\sthe\sdatabase\sfile\sin\srollback\smode.\sThis\sbranch\sis\sunix\sonly\sfor\snow.
-D 2013-03-14T18:34:37.796
+C Allow\sread-only\scursors\sto\suse\smmap\spages\seven\sif\sthere\sis\san\sopen\swrite\stransaction.
+D 2013-03-15T18:29:18.146
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 9a804abbd3cae82d196e4d33aba13239e32522a5
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -121,7 +121,7 @@ F src/auth.c 523da7fb4979469955d822ff9298352d6b31de34
 F src/backup.c b2cac9f7993f3f9588827b824b1501d0c820fa68
 F src/bitvec.c 26675fe8e431dc555e6f2d0e11e651d172234aa1
 F src/btmutex.c 976f45a12e37293e32cae0281b15a21d48a8aaa7
-F src/btree.c c1a956c6762f2a45188c945e1070daec29f5253f
+F src/btree.c 934921ec91456c264f61ce671ca62cb826af977a
 F src/btree.h 3ad7964d6c5b1c7bff569aab6adfa075f8bf06cd
 F src/btreeInt.h eecc84f02375b2bb7a44abbcbbe3747dde73edb2
 F src/build.c 375e5df716e03b9343c5e1211be3b24e6d6dff05
@@ -162,8 +162,8 @@ F src/os.h 027491c77d2404c0a678bb3fb06286f331eb9b57
 F src/os_common.h 92815ed65f805560b66166e3583470ff94478f04
 F src/os_unix.c 2a4cd96aabf413f39cf562baebb27aa9993f6f54
 F src/os_win.c f7da4dc0a2545c0a430080380809946ae4d676d6
-F src/pager.c 4e7e66c2959ee43caf8a7000712d6a4121b0888a
-F src/pager.h 1109a06578ec5574dc2c74cf8d9f69daf36fe3e0
+F src/pager.c 734578514314a3d923fa1399c9722acbcc4f7e6b
+F src/pager.h 81ac95f4fcfe21981f495146f6d7f2fe51afd110
 F src/parse.y 5d5e12772845805fdfeb889163516b84fbb9ae95
 F src/pcache.c f8043b433a57aba85384a531e3937a804432a346
 F src/pcache.h a5e4f5d9f5d592051d91212c5949517971ae6222
@@ -1038,10 +1038,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
 F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
-P 0b452734faa0839c817f040322e7733e423bfce2
-R d4c281f6a900c9b41816881ffb3c2331
-T *branch * experimental-mmap
-T *sym-experimental-mmap *
-T -sym-trunk *
+P 6f21d9cbf5d457e63a7282015a89ae785526cf6d
+R 94aae53403ccd6ebc7d159fa0d23eb33
 U dan
-Z f16a594407ec9e95c26319dfbc751443
+Z 133f9be54c97c4ee392fb0706f346b90
diff --git a/manifest.uuid b/manifest.uuid
index dbbf6a71bc..a20f3a4f02 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6f21d9cbf5d457e63a7282015a89ae785526cf6d
\ No newline at end of file
+b387e2f9d24dccac1fd040e309f6fc7ec1cfffba
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index 038126c3f0..5104625c35 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -1569,13 +1569,17 @@ static int btreeGetPage(
   BtShared *pBt,       /* The btree */
   Pgno pgno,           /* Number of the page to fetch */
   MemPage **ppPage,    /* Return the page in this parameter */
-  int noContent        /* Do not load page content if true */
+  int noContent,       /* Do not load page content if true */
+  int bReadonly        /* True if a read-only (mmap) page is ok */
 ){
   int rc;
   DbPage *pDbPage;
+  int flags = (noContent ? PAGER_ACQUIRE_NOCONTENT : 0) 
+            | (bReadonly ? PAGER_ACQUIRE_READONLY : 0);
 
+  assert( noContent==0 || bReadonly==0 );
   assert( sqlite3_mutex_held(pBt->mutex) );
-  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, noContent);
+  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, flags);
   if( rc ) return rc;
   *ppPage = btreePageFromDbPage(pDbPage, pgno, pBt);
   return SQLITE_OK;
@@ -1618,9 +1622,10 @@ u32 sqlite3BtreeLastPage(Btree *p){
 ** may remain unchanged, or it may be set to an invalid value.
 */
 static int getAndInitPage(
-  BtShared *pBt,          /* The database file */
-  Pgno pgno,           /* Number of the page to get */
-  MemPage **ppPage     /* Write the page pointer here */
+  BtShared *pBt,                  /* The database file */
+  Pgno pgno,                      /* Number of the page to get */
+  MemPage **ppPage,               /* Write the page pointer here */
+  int bReadonly                   /* True if a read-only (mmap) page is ok */
 ){
   int rc;
   assert( sqlite3_mutex_held(pBt->mutex) );
@@ -1628,7 +1633,7 @@ static int getAndInitPage(
   if( pgno>btreePagecount(pBt) ){
     rc = SQLITE_CORRUPT_BKPT;
   }else{
-    rc = btreeGetPage(pBt, pgno, ppPage, 0);
+    rc = btreeGetPage(pBt, pgno, ppPage, 0, bReadonly);
     if( rc==SQLITE_OK ){
       rc = btreeInitPage(*ppPage);
       if( rc!=SQLITE_OK ){
@@ -2350,7 +2355,7 @@ static int lockBtree(BtShared *pBt){
   assert( pBt->pPage1==0 );
   rc = sqlite3PagerSharedLock(pBt->pPager);
   if( rc!=SQLITE_OK ) return rc;
-  rc = btreeGetPage(pBt, 1, &pPage1, 0);
+  rc = btreeGetPage(pBt, 1, &pPage1, 0, 0);
   if( rc!=SQLITE_OK ) return rc;
 
   /* Do some checking to help insure the file we opened really is
@@ -2565,31 +2570,30 @@ int sqlite3BtreeNewDb(Btree *p){
 }
 
 /*
-** If the shared-btree passed as the only argument is holding references
-** to mmap pages, replace them with read/write pages. Return SQLITE_OK
-** if successful, or an error code otherwise.
+** Ensure that any root page references held by open cursors are not
+** mmap pages.
 */
 static int btreeSwapOutMmap(BtShared *pBt){
-  BtCursor *pCsr;
-  for(pCsr=pBt->pCursor; pCsr; pCsr=pCsr->pNext){
-    int i;
-    for(i=0; i<=pCsr->iPage; i++){
-      MemPage *pPg = pCsr->apPage[i];
+  int rc = SQLITE_OK;             /* Return code */
+  BtCursor *pCsr;                 /* Used to iterate through all open cursors */
+
+  for(pCsr=pBt->pCursor; pCsr && rc==SQLITE_OK; pCsr=pCsr->pNext){
+    if( pCsr->iPage>=0 ){
+      MemPage *pPg = pCsr->apPage[0];
       if( pPg->pDbPage->flags & PGHDR_MMAP ){
-        int rc;
         MemPage *pNew = 0;
-        rc = btreeGetPage(pBt, pPg->pgno, &pNew, 0);
-        if( rc==SQLITE_OK && i==pCsr->iPage ){
+        rc = btreeGetPage(pBt, pPg->pgno, &pNew, 0, 0);
+        if( rc==SQLITE_OK && pCsr->iPage==0 ){
           pCsr->info.pCell = pNew->aData + (pCsr->info.pCell - pPg->aData);
         }
-        pCsr->apPage[i] = pNew;
+        pCsr->apPage[0] = pNew;
         releasePage(pPg);
         if( rc!=SQLITE_OK ) return rc;
       }
     }
   }
 
-  return SQLITE_OK;
+  return rc;
 }
 
 /*
@@ -2940,7 +2944,7 @@ static int relocatePage(
   ** iPtrPage.
   */
   if( eType!=PTRMAP_ROOTPAGE ){
-    rc = btreeGetPage(pBt, iPtrPage, &pPtrPage, 0);
+    rc = btreeGetPage(pBt, iPtrPage, &pPtrPage, 0, 0);
     if( rc!=SQLITE_OK ){
       return rc;
     }
@@ -3024,7 +3028,7 @@ static int incrVacuumStep(BtShared *pBt, Pgno nFin, Pgno iLastPg, int bCommit){
       u8 eMode = BTALLOC_ANY;   /* Mode parameter for allocateBtreePage() */
       Pgno iNear = 0;           /* nearby parameter for allocateBtreePage() */
 
-      rc = btreeGetPage(pBt, iLastPg, &pLastPg, 0);
+      rc = btreeGetPage(pBt, iLastPg, &pLastPg, 0, 0);
       if( rc!=SQLITE_OK ){
         return rc;
       }
@@ -3116,8 +3120,11 @@ int sqlite3BtreeIncrVacuum(Btree *p){
     if( nOrig<nFin ){
       rc = SQLITE_CORRUPT_BKPT;
     }else if( nFree>0 ){
-      invalidateAllOverflowCache(pBt);
-      rc = incrVacuumStep(pBt, nFin, nOrig, 0);
+      rc = saveAllCursors(pBt, 0, 0);
+      if( rc==SQLITE_OK ){
+        invalidateAllOverflowCache(pBt);
+        rc = incrVacuumStep(pBt, nFin, nOrig, 0);
+      }
       if( rc==SQLITE_OK ){
         rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
         put4byte(&pBt->pPage1->aData[28], pBt->nPage);
@@ -3438,7 +3445,7 @@ int sqlite3BtreeRollback(Btree *p, int tripCode){
     /* The rollback may have destroyed the pPage1->aData value.  So
     ** call btreeGetPage() on page 1 again to make
     ** sure pPage1->aData is set correctly. */
-    if( btreeGetPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
+    if( btreeGetPage(pBt, 1, &pPage1, 0, 0)==SQLITE_OK ){
       int nPage = get4byte(28+(u8*)pPage1->aData);
       testcase( nPage==0 );
       if( nPage==0 ) sqlite3PagerPagecount(pBt->pPager, &nPage);
@@ -3872,7 +3879,7 @@ static int getOverflowPage(
 
   assert( next==0 || rc==SQLITE_DONE );
   if( rc==SQLITE_OK ){
-    rc = btreeGetPage(pBt, ovfl, &pPage, 0);
+    rc = btreeGetPage(pBt, ovfl, &pPage, 0, (ppPage==0));
     assert( rc==SQLITE_OK || pPage==0 );
     if( rc==SQLITE_OK ){
       next = get4byte(pPage->aData);
@@ -4093,7 +4100,9 @@ static int accessPayload(
 
         {
           DbPage *pDbPage;
-          rc = sqlite3PagerGet(pBt->pPager, nextPage, &pDbPage);
+          rc = sqlite3PagerAcquire(pBt->pPager, nextPage, &pDbPage,
+              (eOp==0 ? PAGER_ACQUIRE_READONLY : 0)
+          );
           if( rc==SQLITE_OK ){
             aPayload = sqlite3PagerGetData(pDbPage);
             nextPage = get4byte(aPayload);
@@ -4272,10 +4281,11 @@ static int moveToChild(BtCursor *pCur, u32 newPgno){
   assert( cursorHoldsMutex(pCur) );
   assert( pCur->eState==CURSOR_VALID );
   assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
+  assert( pCur->iPage>=0 );
   if( pCur->iPage>=(BTCURSOR_MAX_DEPTH-1) ){
     return SQLITE_CORRUPT_BKPT;
   }
-  rc = getAndInitPage(pBt, newPgno, &pNewPage);
+  rc = getAndInitPage(pBt, newPgno, &pNewPage, (pCur->wrFlag==0));
   if( rc ) return rc;
   pCur->apPage[i+1] = pNewPage;
   pCur->aiIdx[i+1] = 0;
@@ -4392,7 +4402,7 @@ static int moveToRoot(BtCursor *pCur){
     pCur->eState = CURSOR_INVALID;
     return SQLITE_OK;
   }else{
-    rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->apPage[0]);
+    rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->apPage[0], 0);
     if( rc!=SQLITE_OK ){
       pCur->eState = CURSOR_INVALID;
       return rc;
@@ -5006,7 +5016,7 @@ static int allocateBtreePage(
       if( iTrunk>mxPage ){
         rc = SQLITE_CORRUPT_BKPT;
       }else{
-        rc = btreeGetPage(pBt, iTrunk, &pTrunk, 0);
+        rc = btreeGetPage(pBt, iTrunk, &pTrunk, 0, 0);
       }
       if( rc ){
         pTrunk = 0;
@@ -5070,7 +5080,7 @@ static int allocateBtreePage(
             goto end_allocate_page;
           }
           testcase( iNewTrunk==mxPage );
-          rc = btreeGetPage(pBt, iNewTrunk, &pNewTrunk, 0);
+          rc = btreeGetPage(pBt, iNewTrunk, &pNewTrunk, 0, 0);
           if( rc!=SQLITE_OK ){
             goto end_allocate_page;
           }
@@ -5150,7 +5160,7 @@ static int allocateBtreePage(
           }
           put4byte(&aData[4], k-1);
           noContent = !btreeGetHasContent(pBt, *pPgno);
-          rc = btreeGetPage(pBt, *pPgno, ppPage, noContent);
+          rc = btreeGetPage(pBt, *pPgno, ppPage, noContent, 0);
           if( rc==SQLITE_OK ){
             rc = sqlite3PagerWrite((*ppPage)->pDbPage);
             if( rc!=SQLITE_OK ){
@@ -5198,7 +5208,7 @@ static int allocateBtreePage(
       MemPage *pPg = 0;
       TRACE(("ALLOCATE: %d from end of file (pointer-map page)\n", pBt->nPage));
       assert( pBt->nPage!=PENDING_BYTE_PAGE(pBt) );
-      rc = btreeGetPage(pBt, pBt->nPage, &pPg, bNoContent);
+      rc = btreeGetPage(pBt, pBt->nPage, &pPg, bNoContent, 0);
       if( rc==SQLITE_OK ){
         rc = sqlite3PagerWrite(pPg->pDbPage);
         releasePage(pPg);
@@ -5212,7 +5222,7 @@ static int allocateBtreePage(
     *pPgno = pBt->nPage;
 
     assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
-    rc = btreeGetPage(pBt, *pPgno, ppPage, bNoContent);
+    rc = btreeGetPage(pBt, *pPgno, ppPage, bNoContent, 0);
     if( rc ) return rc;
     rc = sqlite3PagerWrite((*ppPage)->pDbPage);
     if( rc!=SQLITE_OK ){
@@ -5280,7 +5290,7 @@ static int freePage2(BtShared *pBt, MemPage *pMemPage, Pgno iPage){
     /* If the secure_delete option is enabled, then
     ** always fully overwrite deleted information with zeros.
     */
-    if( (!pPage && ((rc = btreeGetPage(pBt, iPage, &pPage, 0))!=0) )
+    if( (!pPage && ((rc = btreeGetPage(pBt, iPage, &pPage, 0, 0))!=0) )
      ||            ((rc = sqlite3PagerWrite(pPage->pDbPage))!=0)
     ){
       goto freepage_out;
@@ -5307,7 +5317,7 @@ static int freePage2(BtShared *pBt, MemPage *pMemPage, Pgno iPage){
     u32 nLeaf;                /* Initial number of leaf cells on trunk page */
 
     iTrunk = get4byte(&pPage1->aData[32]);
-    rc = btreeGetPage(pBt, iTrunk, &pTrunk, 0);
+    rc = btreeGetPage(pBt, iTrunk, &pTrunk, 0, 0);
     if( rc!=SQLITE_OK ){
       goto freepage_out;
     }
@@ -5353,7 +5363,7 @@ static int freePage2(BtShared *pBt, MemPage *pMemPage, Pgno iPage){
   ** first trunk in the free-list is full. Either way, the page being freed
   ** will become the new first trunk page in the free-list.
   */
-  if( pPage==0 && SQLITE_OK!=(rc = btreeGetPage(pBt, iPage, &pPage, 0)) ){
+  if( pPage==0 && SQLITE_OK!=(rc = btreeGetPage(pBt, iPage, &pPage, 0, 0)) ){
     goto freepage_out;
   }
   rc = sqlite3PagerWrite(pPage->pDbPage);
@@ -6154,7 +6164,7 @@ static int balance_nonroot(
   }
   pgno = get4byte(pRight);
   while( 1 ){
-    rc = getAndInitPage(pBt, pgno, &apOld[i]);
+    rc = getAndInitPage(pBt, pgno, &apOld[i], 0);
     if( rc ){
       memset(apOld, 0, (i+1)*sizeof(MemPage*));
       goto balance_cleanup;
@@ -7245,7 +7255,7 @@ static int btreeCreateTable(Btree *p, int *piTable, int createTabFlags){
       releasePage(pPageMove);
 
       /* Move the page currently at pgnoRoot to pgnoMove. */
-      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0);
+      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0, 0);
       if( rc!=SQLITE_OK ){
         return rc;
       }
@@ -7266,7 +7276,7 @@ static int btreeCreateTable(Btree *p, int *piTable, int createTabFlags){
       if( rc!=SQLITE_OK ){
         return rc;
       }
-      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0);
+      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0, 0);
       if( rc!=SQLITE_OK ){
         return rc;
       }
@@ -7342,7 +7352,7 @@ static int clearDatabasePage(
     return SQLITE_CORRUPT_BKPT;
   }
 
-  rc = getAndInitPage(pBt, pgno, &pPage);
+  rc = getAndInitPage(pBt, pgno, &pPage, 0);
   if( rc ) return rc;
   for(i=0; i<pPage->nCell; i++){
     pCell = findCell(pPage, i);
@@ -7444,7 +7454,7 @@ static int btreeDropTable(Btree *p, Pgno iTable, int *piMoved){
     return SQLITE_LOCKED_SHAREDCACHE;
   }
 
-  rc = btreeGetPage(pBt, (Pgno)iTable, &pPage, 0);
+  rc = btreeGetPage(pBt, (Pgno)iTable, &pPage, 0, 0);
   if( rc ) return rc;
   rc = sqlite3BtreeClearTable(p, iTable, 0);
   if( rc ){
@@ -7479,7 +7489,7 @@ static int btreeDropTable(Btree *p, Pgno iTable, int *piMoved){
         */
         MemPage *pMove;
         releasePage(pPage);
-        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0);
+        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0, 0);
         if( rc!=SQLITE_OK ){
           return rc;
         }
@@ -7489,7 +7499,7 @@ static int btreeDropTable(Btree *p, Pgno iTable, int *piMoved){
           return rc;
         }
         pMove = 0;
-        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0);
+        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0, 0);
         freePage(pMove, &rc);
         releasePage(pMove);
         if( rc!=SQLITE_OK ){
@@ -7901,7 +7911,7 @@ static int checkTreePage(
   usableSize = pBt->usableSize;
   if( iPage==0 ) return 0;
   if( checkRef(pCheck, iPage, zParentContext) ) return 0;
-  if( (rc = btreeGetPage(pBt, (Pgno)iPage, &pPage, 0))!=0 ){
+  if( (rc = btreeGetPage(pBt, (Pgno)iPage, &pPage, 0, 0))!=0 ){
     checkAppendMsg(pCheck, zContext,
        "unable to get the page. error code=%d", rc);
     return 0;
diff --git a/src/pager.c b/src/pager.c
index c362494093..8470e7e35e 100644
--- a/src/pager.c
+++ b/src/pager.c
@@ -658,6 +658,7 @@ struct Pager {
 
   void *pMap;                 /* Memory mapped prefix of database file */
   i64 nMap;                   /* Size of mapping at pMap in bytes */ 
+  i64 nMapValid;              /* Bytes at pMap known to be valid */
   int nMmapOut;               /* Number of mmap pages currently outstanding */
   PgHdr *pFree;               /* List of free mmap page headers (pDirty) */
   /*
@@ -2512,6 +2513,9 @@ static int pager_truncate(Pager *pPager, Pgno nPage){
     if( rc==SQLITE_OK && currentSize!=newSize ){
       if( currentSize>newSize ){
         rc = sqlite3OsTruncate(pPager->fd, newSize);
+        if( newSize<pPager->nMapValid ){
+          pPager->nMapValid = newSize;
+        }
       }else if( (currentSize+szPage)<=newSize ){
         char *pTmp = pPager->pTmpSpace;
         memset(pTmp, 0, szPage);
@@ -3818,6 +3822,7 @@ static int pagerUnmap(Pager *pPager){
     munmap(pPager->pMap, pPager->nMap);
     pPager->pMap = 0;
     pPager->nMap = 0;
+    pPager->nMapValid = 0;
   }
   return SQLITE_OK;
 }
@@ -3839,7 +3844,7 @@ static int pagerMap(Pager *pPager){
         return SQLITE_IOERR;
       }
       pPager->pMap = pMap;
-      pPager->nMap = sz;
+      pPager->nMapValid = pPager->nMap = sz;
     }
   }
 
@@ -3858,7 +3863,9 @@ static int pagerAcquireMapPage(Pager *pPager, Pgno pgno, PgHdr **ppPage){
       if( rc!=SQLITE_OK ) return rc;
     }
 
-    if( pgno!=1 && pPager->pMap && pPager->nMap>=((i64)pgno*pPager->pageSize) ){
+    if( pgno!=1 && pPager->pMap 
+     && pPager->nMapValid>=((i64)pgno*pPager->pageSize) 
+    ){
       PgHdr *p;
       if( pPager->pFree ){
         p = pPager->pFree;
@@ -5035,9 +5042,11 @@ int sqlite3PagerSharedLock(Pager *pPager){
       );
     }
 
-    if( !pPager->tempFile 
-     && (pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0) 
-    ){
+    if( !pPager->tempFile && (
+        pPager->pBackup 
+     || sqlite3PcachePagecount(pPager->pPCache)>0 
+     || pPager->pMap
+    )){
       /* The shared-lock has just been acquired on the database file
       ** and there are already pages in the cache (from a previous
       ** read or write transaction).  Check to see if the database
@@ -5072,6 +5081,15 @@ int sqlite3PagerSharedLock(Pager *pPager){
 
       if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
         pager_reset(pPager);
+
+        /* Unmap the database file. It is possible that external processes
+        ** may have truncated the database file and then extended it back
+        ** to its original size while this process was not holding a lock.
+        ** In this case there may exist a Pager.pMap mapping that appears
+        ** to be the right size but is not actually valid. Avoid this
+        ** possibility by unmapping the db here. */
+        pagerUnmap(pPager);
+      }else if( ((i64)nPage*pPager->pageSize)!=pPager->nMap ){
         pagerUnmap(pPager);
       }
     }
@@ -5173,10 +5191,20 @@ int sqlite3PagerAcquire(
   Pager *pPager,      /* The pager open on the database file */
   Pgno pgno,          /* Page number to fetch */
   DbPage **ppPage,    /* Write a pointer to the page here */
-  int noContent       /* Do not bother reading content from disk if true */
+  int flags           /* PAGER_ACQUIRE_XXX flags */
 ){
-  int rc;
-  PgHdr *pPg;
+  int rc = SQLITE_OK;
+  PgHdr *pPg = 0;
+  const int noContent = (flags & PAGER_ACQUIRE_NOCONTENT);
+
+  /* It is acceptable to use a read-only (mmap) page for any page except
+  ** page 1 if there is no write-transaction open or the ACQUIRE_READONLY
+  ** flag was specified by the caller. And so long as the db is not a 
+  ** temporary or in-memory database.  */
+  const int bMmapOk = (
+      (pgno!=1 && pPager->pWal==0 && !pPager->tempFile && !MEMDB)
+   && (pPager->eState==PAGER_READER || (flags & PAGER_ACQUIRE_READONLY))
+  );
 
   assert( pPager->eState>=PAGER_READER );
   assert( assert_pager_state(pPager) );
@@ -5190,12 +5218,23 @@ int sqlite3PagerAcquire(
   if( pPager->errCode!=SQLITE_OK ){
     rc = pPager->errCode;
   }else{
-    if( pPager->eState==PAGER_READER && pPager->pWal==0 ){
-      rc = pagerAcquireMapPage(pPager, pgno, &pPg);
-      if( rc!=SQLITE_OK ) goto pager_acquire_err;
-      if( pPg ){
-        *ppPage = pPg;
-        return SQLITE_OK;
+
+    if( bMmapOk ){
+      if( pPager->pMap==0 ) rc = pagerMap(pPager);
+      if( rc==SQLITE_OK && pPager->nMap>=((i64)pgno * pPager->pageSize) ){
+        if( pPager->eState>PAGER_READER ){
+          (void)sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
+        }
+        if( pPg==0 ){
+          rc = pagerAcquireMapPage(pPager, pgno, &pPg);
+        }
+        if( pPg ){
+          assert( rc==SQLITE_OK );
+          *ppPage = pPg;
+          return SQLITE_OK;
+        }else if( rc!=SQLITE_OK ){
+          goto pager_acquire_err;
+        }
       }
     }
 
@@ -5433,8 +5472,6 @@ int sqlite3PagerBegin(Pager *pPager, int exFlag, int subjInMemory){
   assert( pPager->eState>=PAGER_READER && pPager->eState<PAGER_ERROR );
   pPager->subjInMemory = (u8)subjInMemory;
 
-  pagerUnmap(pPager);
-
   if( ALWAYS(pPager->eState==PAGER_READER) ){
     assert( pPager->pInJournal==0 );
 
@@ -5653,13 +5690,11 @@ int sqlite3PagerWrite(DbPage *pDbPage){
   Pager *pPager = pPg->pPager;
   Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);
 
+  assert( (pPg->flags & PGHDR_MMAP)==0 );
   assert( pPager->eState>=PAGER_WRITER_LOCKED );
   assert( pPager->eState!=PAGER_ERROR );
   assert( assert_pager_state(pPager) );
 
-  /* There must not be any outstanding mmap pages at this point */
-  assert( pPager->nMmapOut==0 );
-
   if( nPagePerSector>1 ){
     Pgno nPageCount;          /* Total number of pages in database file */
     Pgno pg1;                 /* First page of the sector pPg is located on. */
diff --git a/src/pager.h b/src/pager.h
index 90f8e6af78..94957dac60 100644
--- a/src/pager.h
+++ b/src/pager.h
@@ -78,6 +78,12 @@ typedef struct PgHdr DbPage;
 #define PAGER_JOURNALMODE_MEMORY      4   /* In-memory journal file */
 #define PAGER_JOURNALMODE_WAL         5   /* Use write-ahead logging */
 
+/*
+** Flags that make up the mask passed to sqlite3PagerAcquire().
+*/
+#define PAGER_ACQUIRE_NOCONTENT     0x01  /* Do not load data from disk */
+#define PAGER_ACQUIRE_READONLY      0x02  /* Read-only page is acceptable */
+
 /*
 ** The remainder of this file contains the declarations of the functions
 ** that make up the Pager sub-system API. See source code comments for