Experimental change to the xShmXXX parts of the VFS interface.

FossilOrigin-Name: ca68472db01c14a899892007d1cbaff5e86ae193

manifest

@@ -1,8 +1,5 @@
------BEGIN PGP SIGNED MESSAGE-----
+C Experimental\schange\sto\sthe\sxShmXXX\sparts\sof\sthe\sVFS\sinterface.
-Hash: SHA1
+D 2010-06-11T19:04:21
-
-C Refactor\sand\ssimplify\sthe\slogic\sused\sto\schange\sjournalmode.
-D 2010-06-11T17:01:25
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in a5cad1f8f3e021356bfcc6c77dc16f6f1952bbc3
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -153,11 +150,11 @@ F src/mutex_os2.c 6a62583e374ba3ac1a3fcc0da2bfdac7d3942689
 F src/mutex_unix.c cf84466b4fdd2baa0d5a10bb19f08b2abc1ce42e
 F src/mutex_w32.c 1fe0e735897be20e09dd6f53c3fb516c6b48c0eb
 F src/notify.c cbfa66a836da3a51567209636e6a94059c137930
-F src/os.c 1516984144e26734f97748f891f1a04f9e294c2e
+F src/os.c 00ab9dcdee6e33ff3d060744c86af25200c51e0f
-F src/os.h 6f529984a29511c7a3479cfe549c10bfa131532f
+F src/os.h a0d2c1436cb6003e6da16001499a0b828f1edb34
 F src/os_common.h a8f95b81eca8a1ab8593d23e94f8a35f35d4078f
 F src/os_os2.c 665876d5eec7585226b0a1cf5e18098de2b2da19
-F src/os_unix.c 12051d37e533cdaa8bb13c9d9fe2a13e08552187
+F src/os_unix.c 29dac62790ccea7db1516be3abb007988accb165
 F src/os_win.c 0cf1f571546f165001e2391b5d4a4a16d86977d3
 F src/pager.c 2964185d4356d0dc159b8340e52d2538d32394e5
 F src/pager.h ca1f23c0cf137ac26f8908df2427c8b308361efd
@@ -173,7 +170,7 @@ F src/resolve.c ac5f1a713cd1ae77f08b83cc69581e11bf5ae6f9
 F src/rowset.c 69afa95a97c524ba6faf3805e717b5b7ae85a697
 F src/select.c c03d8a0565febcde8c6a12c5d77d065fddae889b
 F src/shell.c fd4ccdb37c3b68de0623eb938a649e0990710714
-F src/sqlite.h.in b6a64327e174cf725e57dd93ddf1e97c52dd41e2
+F src/sqlite.h.in 092df034f4b426ffbb9e5bb905958fa35bbb7f7a
 F src/sqlite3ext.h 69dfb8116af51b84a029cddb3b35062354270c89
 F src/sqliteInt.h 242987ebd2366ea36650a09cdab04a9163c62109
 F src/sqliteLimit.h 196e2f83c3b444c4548fc1874f52f84fdbda40f3
@@ -195,7 +192,7 @@ F src/test_backup.c c129c91127e9b46e335715ae2e75756e25ba27de
 F src/test_btree.c 47cd771250f09cdc6e12dda5bc71bc0b3abc96e2
 F src/test_config.c 6210f501d358bde619ae761f06f123529c6ba24f
 F src/test_demovfs.c da81a5f7785bb352bda7911c332a983ec4f17f27
-F src/test_devsym.c 709712f5157667410cd0dad1b7b1b54319c122c5
+F src/test_devsym.c cf64a4b602ccde10c9261283d1b9be12f4c4a0ea
 F src/test_func.c 13b582345fb1185a93e46c53310fae8547dcce20
 F src/test_hexio.c 1237f000ec7a491009b1233f5c626ea71bce1ea2
 F src/test_init.c 5d624ffd0409d424cf9adbfe1f056b200270077c
@@ -212,7 +209,7 @@ F src/test_schema.c 8c06ef9ddb240c7a0fcd31bc221a6a2aade58bf0
 F src/test_server.c bbba05c144b5fc4b52ff650a4328027b3fa5fcc6
 F src/test_tclvar.c f4dc67d5f780707210d6bb0eb6016a431c04c7fa
 F src/test_thread.c aa9919c885a1fe53eafc73492f0898ee6c0a0726
-F src/test_vfs.c d329e3ea93624f65d7b6a46209861ddecea4e21d
+F src/test_vfs.c b83206d2c04b3ba84d8d85420c4c7573c58feba5
 F src/test_wsd.c 41cadfd9d97fe8e3e4e44f61a4a8ccd6f7ca8fe9
 F src/tokenize.c 25ceb0f0a746ea1d0f9553787f3f0a56853cfaeb
 F src/trigger.c 8927588cb9e6d47f933b53bfe74200fbb504100d
@@ -229,7 +226,7 @@ F src/vdbeblob.c 5327132a42a91e8b7acfb60b9d2c3b1c5c863e0e
 F src/vdbemem.c 2a82f455f6ca6f78b59fb312f96054c04ae0ead1
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c 2cdfea9a5e50e4dde48767e69e1fead2ff1781cd
+F src/wal.c 0aa364734d6daca75771944fc2b4a8f36e63fc4e
 F src/wal.h 4ace25262452d17e7d3ec970c89ee17794004008
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c 1c895bef33d0dfc7ed90fb1f74120435d210ea56
@@ -540,7 +537,7 @@ F test/pageropt.test 8146bf448cf09e87bb1867c2217b921fb5857806
 F test/pagesize.test 76aa9f23ecb0741a4ed9d2e16c5fa82671f28efb
 F test/pcache.test eebc4420b37cb07733ae9b6e99c9da7c40dd6d58
 F test/pcache2.test 0d85f2ab6963aee28c671d4c71bec038c00a1d16
-F test/permutations.test ad10d7b31b4a585977380886c832e2ac13c41237
+F test/permutations.test 64fbafa685149be54a1ceb545942911f998c604d
 F test/pragma.test 6960f9efbce476f70ba9ee2171daf5042f9e3d8a
 F test/pragma2.test 5364893491b9231dd170e3459bfc2e2342658b47
 F test/printf.test 05970cde31b1a9f54bd75af60597be75a5c54fea
@@ -768,8 +765,8 @@ F test/vtab_alter.test 9e374885248f69e251bdaacf480b04a197f125e5
 F test/vtab_err.test 0d4d8eb4def1d053ac7c5050df3024fd47a3fbd8
 F test/vtab_shared.test 0eff9ce4f19facbe0a3e693f6c14b80711a4222d
 F test/wal.test 0a599c3c4812ed92bc7ad9efcc2c4007fe4cc99a
-F test/wal2.test 854a2b409450f1cb756c2bbd1e87e30740094357
+F test/wal2.test f9dce93acecff697fc1935869b1ae4cb7dc14587
-F test/wal3.test ae876ff988af5b2b34d27474e0dd1a8c84e9bbcb
+F test/wal3.test 1d3aee1a0295db941a0323c0ce5ac16bd5b7689d
 F test/wal_common.tcl 3e953ae60919281688ea73e4d0aa0e1bc94becd9
 F test/walbak.test e7650a26eb4b8abeca9b145b1af1e63026dde432
 F test/walcksum.test 4efa8fb88c32bed8288ea4385a9cc113a5c8f0bf
@@ -823,14 +820,10 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P af353bd89e5ec89f113d217225cc59cbc8373d64
+P 95cc3f6fdec5494560c3cd4439d06870d1c62506
-R 3e2d7a9cc84ff16ee3e947d8ce602cce
+R 05bb7be31606a33c54980de0a121cf7e
-U drh
+T *branch * experimental
-Z e14f3acbecbf2df0abe6fde12480ec15
+T *sym-experimental *
------BEGIN PGP SIGNATURE-----
+T -sym-trunk *
-Version: GnuPG v1.4.6 (GNU/Linux)
+U dan
-
+Z 7e046a655e9f9112461a59731e31d3dc
-iD8DBQFMEmvooxKgR168RlERAg5RAJ9VmP08NyW1of8QWkDMnAiHK8A/xgCeLBcs
-hbn4o1Zj2vKA/g5KFcfNycs=
-=Li8t
------END PGP SIGNATURE-----

manifest.uuid

@@ -1 +1 @@
-95cc3f6fdec5494560c3cd4439d06870d1c62506
+ca68472db01c14a899892007d1cbaff5e86ae193

src/os.c

@@ -119,6 +119,15 @@ void sqlite3OsShmBarrier(sqlite3_file *id){
 int sqlite3OsShmClose(sqlite3_file *id, int deleteFlag){
   return id->pMethods->xShmClose(id, deleteFlag);
 }
+int sqlite3OsShmPage(
+  sqlite3_file *id, 
+  int iPage, 
+  int pgsz, 
+  int isWrite, 
+  void volatile **pp
+){
+  return id->pMethods->xShmPage(id, iPage, pgsz, isWrite, pp);
+}
 
 /*
 ** The next group of routines are convenience wrappers around the

src/os.h

@@ -254,6 +254,7 @@ int sqlite3OsShmRelease(sqlite3_file *id);
 int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
 void sqlite3OsShmBarrier(sqlite3_file *id);
 int sqlite3OsShmClose(sqlite3_file *id, int);
+int sqlite3OsShmPage(sqlite3_file *,int,int,int,void volatile **);
 
 /* 
 ** Functions for accessing sqlite3_vfs methods 

src/os_unix.c

@@ -3141,8 +3141,14 @@ struct unixShmNode {
   sqlite3_mutex *mutexBuf;   /* Mutex to access zBuf[] */
   char *zFilename;           /* Name of the mmapped file */
   int h;                     /* Open file descriptor */
+
   int szMap;                 /* Size of the mapping into memory */
   char *pMMapBuf;            /* Where currently mmapped().  NULL if unmapped */
+
+  int pgsz;                  /* Size of shared-memory pages */
+  int nPage;                 /* Size of array apPage */
+  char **apPage;             /* Array of mapped shared-memory pages */
+
   int nRef;                  /* Number of unixShm objects pointing to this */
   unixShm *pFirst;           /* All unixShm objects pointing to this */
 #ifdef SQLITE_DEBUG
@@ -3266,10 +3272,15 @@ static void unixShmPurge(unixFile *pFd){
   unixShmNode *p = pFd->pInode->pShmNode;
   assert( unixMutexHeld() );
   if( p && p->nRef==0 ){
+    int i;
     assert( p->pInode==pFd->pInode );
     if( p->mutex ) sqlite3_mutex_free(p->mutex);
     if( p->mutexBuf ) sqlite3_mutex_free(p->mutexBuf);
     if( p->pMMapBuf ) munmap(p->pMMapBuf, p->szMap);
+    for(i=0; i<p->nPage; i++){
+      munmap(p->apPage[i], p->pgsz);
+    }
+    sqlite3_free(p->apPage);
     if( p->h>=0 ) close(p->h);
     p->pInode->pShmNode = 0;
     sqlite3_free(p);
@@ -3706,6 +3717,71 @@ static void unixShmBarrier(
   unixLeaveMutex();
 }
 
+static int unixShmPage(
+  sqlite3_file *fd,               /* Handle open on database file */
+  int iPage,                      /* Page to retrieve */
+  int pgsz,                       /* Size of pages */
+  int isWrite,                    /* True to extend file if necessary */
+  void volatile **pp              /* OUT: Mapped memory */
+){
+  unixFile *pDbFd = (unixFile*)fd;
+  unixShm *p = pDbFd->pShm;
+  unixShmNode *pShmNode = p->pShmNode;
+  int rc = SQLITE_OK;
+
+  assert( p->hasMutexBuf==0 );
+  sqlite3_mutex_enter(pShmNode->mutexBuf);
+  assert( pgsz==pShmNode->pgsz || pShmNode->nPage==0 );
+
+  if( pShmNode->nPage<=iPage ){
+    char **apNew;                 /* New apPage[] array */
+    int nByte = (iPage+1)*pgsz;   /* Minimum required file size */
+    struct stat sStat;
+
+    pShmNode->pgsz = pgsz;
+
+    /* Make sure the underlying file is large enough (or fail) */
+    if( fstat(pShmNode->h, &sStat) ){
+      rc = SQLITE_IOERR_SHMSIZE;
+      goto shmpage_out;
+    }else if( sStat.st_size<nByte ){
+      if( !isWrite ) goto shmpage_out;
+      if( ftruncate(pShmNode->h, nByte) ){
+        rc = SQLITE_IOERR_SHMSIZE;
+        goto shmpage_out;
+      }  
+    }
+
+    apNew = (char**)sqlite3_realloc(pShmNode->apPage, (iPage+1)*sizeof(char *));
+    if( !apNew ){
+      rc = SQLITE_IOERR_NOMEM;
+      goto shmpage_out;
+    }
+    pShmNode->apPage = apNew;
+
+    while(pShmNode->nPage<=iPage){
+      void *pMem = mmap(
+          0, pgsz, PROT_READ|PROT_WRITE, MAP_SHARED, pShmNode->h, iPage*pgsz
+      );
+      if( pMem==MAP_FAILED ){
+        assert(0);
+        rc = SQLITE_IOERR;
+        goto shmpage_out;
+      }
+      pShmNode->apPage[pShmNode->nPage] = pMem;
+      pShmNode->nPage++;
+    }
+  }
+
+shmpage_out:
+  if( pShmNode->nPage>iPage ){
+    *pp = pShmNode->apPage[iPage];
+  }else{
+    *pp = 0;
+  }
+  sqlite3_mutex_leave(pShmNode->mutexBuf);
+  return rc;
+}
 
 #else
 # define unixShmOpen    0
@@ -3715,6 +3791,7 @@ static void unixShmBarrier(
 # define unixShmLock    0
 # define unixShmBarrier 0
 # define unixShmClose   0
+# define unixShmPage    0
 #endif /* #ifndef SQLITE_OMIT_WAL */
 
 /*
@@ -3778,7 +3855,8 @@ static const sqlite3_io_methods METHOD = {                                   \
    unixShmRelease,             /* xShmRelease */                             \
    unixShmLock,                /* xShmLock */                                \
    unixShmBarrier,             /* xShmBarrier */                             \
-   unixShmClose                /* xShmClose */                               \
+   unixShmClose,               /* xShmClose */                               \
+   unixShmPage                 /* xShmPage */                                \
 };                                                                           \
 static const sqlite3_io_methods *FINDER##Impl(const char *z, unixFile *p){   \
   UNUSED_PARAMETER(z); UNUSED_PARAMETER(p);                                  \

src/sqlite.h.in

@@ -666,6 +666,7 @@ struct sqlite3_io_methods {
   int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
   void (*xShmBarrier)(sqlite3_file*);
   int (*xShmClose)(sqlite3_file*, int deleteFlag);
+  int (*xShmPage)(sqlite3_file*, int iPage, int pgsz, int, void volatile**);
   /* Methods above are valid for version 2 */
   /* Additional methods may be added in future releases */
 };

src/test_devsym.c

@@ -57,6 +57,7 @@ static int devsymShmRelease(sqlite3_file*);
 static int devsymShmLock(sqlite3_file*,int,int,int);
 static void devsymShmBarrier(sqlite3_file*);
 static int devsymShmClose(sqlite3_file*,int);
+static int devsymShmPage(sqlite3_file*,int,int,int, void volatile **);
 
 /*
 ** Method declarations for devsym_vfs.
@@ -125,7 +126,8 @@ static sqlite3_io_methods devsym_io_methods = {
   devsymShmRelease,                 /* xShmRelease */
   devsymShmLock,                    /* xShmLock */
   devsymShmBarrier,                 /* xShmBarrier */
-  devsymShmClose                    /* xShmClose */
+  devsymShmClose,                   /* xShmClose */
+  devsymShmPage                     /* xShmPage */
 };
 
 struct DevsymGlobal {
@@ -275,6 +277,16 @@ static int devsymShmClose(sqlite3_file *pFile, int delFlag){
   devsym_file *p = (devsym_file *)pFile;
   return sqlite3OsShmClose(p->pReal, delFlag);
 }
+static int devsymShmPage(
+  sqlite3_file *pFile, 
+  int iPage, 
+  int pgsz, 
+  int isWrite, 
+  void volatile **pp
+){
+  devsym_file *p = (devsym_file *)pFile;
+  return sqlite3OsShmPage(p->pReal, iPage, pgsz, isWrite, pp);
+}
 
 
 

src/test_vfs.c

@@ -75,10 +75,14 @@ struct Testvfs {
 #define TESTVFS_SHMLOCK_MASK    0x00000010
 #define TESTVFS_SHMBARRIER_MASK 0x00000020
 #define TESTVFS_SHMCLOSE_MASK   0x00000040
+#define TESTVFS_SHMPAGE_MASK    0x00000080
 
-#define TESTVFS_OPEN_MASK       0x00000080
+#define TESTVFS_OPEN_MASK       0x00000100
-#define TESTVFS_SYNC_MASK       0x00000100
+#define TESTVFS_SYNC_MASK       0x00000200
-#define TESTVFS_ALL_MASK        0x000001FF
+#define TESTVFS_ALL_MASK        0x000003FF
+
+
+#define TESTVFS_MAX_PAGES 256
 
 /*
 ** A shared-memory buffer. There is one of these objects for each shared
@@ -87,8 +91,8 @@ struct Testvfs {
 */
 struct TestvfsBuffer {
   char *zFile;                    /* Associated file name */
-  int n;                          /* Size of allocated buffer in bytes */
+  int pgsz;                       /* Page size */
-  u8 *a;                          /* Buffer allocated using ckalloc() */
+  u8 *aPage[TESTVFS_MAX_PAGES];   /* Array of ckalloc'd pages */
   TestvfsFile *pFile;             /* List of open handles */
   TestvfsBuffer *pNext;           /* Next in linked list of all buffers */
 };
@@ -139,6 +143,7 @@ static int tvfsShmRelease(sqlite3_file*);
 static int tvfsShmLock(sqlite3_file*, int , int, int);
 static void tvfsShmBarrier(sqlite3_file*);
 static int tvfsShmClose(sqlite3_file*, int);
+static int tvfsShmPage(sqlite3_file*,int,int,int, void volatile **);
 
 static sqlite3_io_methods tvfs_io_methods = {
   2,                            /* iVersion */
@@ -160,7 +165,8 @@ static sqlite3_io_methods tvfs_io_methods = {
   tvfsShmRelease,                 /* xShmRelease */
   tvfsShmLock,                    /* xShmLock */
   tvfsShmBarrier,                 /* xShmBarrier */
-  tvfsShmClose                    /* xShmClose */
+  tvfsShmClose,                   /* xShmClose */
+  tvfsShmPage                     /* xShmPage */
 };
 
 static int tvfsResultCode(Testvfs *p, int *pRc){
@@ -547,16 +553,6 @@ static int tvfsCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
   return PARENTVFS(pVfs)->xCurrentTime(PARENTVFS(pVfs), pTimeOut);
 }
 
-static void tvfsGrowBuffer(TestvfsFile *pFd, int reqSize, int *pNewSize){
-  TestvfsBuffer *pBuffer = pFd->pShm;
-  if( reqSize>pBuffer->n ){
-    pBuffer->a = (u8 *)ckrealloc((char *)pBuffer->a, reqSize);
-    memset(&pBuffer->a[pBuffer->n], 0x55, reqSize-pBuffer->n);
-    pBuffer->n = reqSize;
-  }
-  *pNewSize = pBuffer->n;
-}
-
 static int tvfsInjectIoerr(Testvfs *p){
   int ret = 0;
   if( p->ioerr ){
@@ -624,66 +620,66 @@ static int tvfsShmSize(
   int reqSize,
   int *pNewSize
 ){
-  int rc = SQLITE_OK;
+  assert(0);
-  TestvfsFile *pFd = (TestvfsFile *)pFile;
+  return SQLITE_OK;
-  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);
-
-  if( p->pScript && p->mask&TESTVFS_SHMSIZE_MASK ){
-    tvfsExecTcl(p, "xShmSize", 
-        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
-    );
-    tvfsResultCode(p, &rc);
-  }
-  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMSIZE_MASK && tvfsInjectIoerr(p) ){
-    rc = SQLITE_IOERR;
-  }
-  if( rc==SQLITE_OK ){
-    tvfsGrowBuffer(pFd, reqSize, pNewSize);
-  }
-  return rc;
 }
-
 static int tvfsShmGet(
   sqlite3_file *pFile, 
   int reqMapSize, 
   int *pMapSize, 
   volatile void **pp
+){
+  assert(0);
+  return SQLITE_OK;
+}
+static int tvfsShmRelease(sqlite3_file *pFile){
+  assert(0);
+  return SQLITE_OK;
+}
+
+static void tvfsAllocPage(TestvfsBuffer *p, int iPage, int pgsz){
+  assert( iPage<TESTVFS_MAX_PAGES );
+  if( p->aPage[iPage]==0 ){
+    p->aPage[iPage] = ckalloc(pgsz);
+    memset(p->aPage[iPage], 0, pgsz);
+    p->pgsz = pgsz;
+  }
+}
+
+static int tvfsShmPage(
+  sqlite3_file *pFile,            /* Handle open on database file */
+  int iPage,                      /* Page to retrieve */
+  int pgsz,                       /* Size of pages */
+  int isWrite,                    /* True to extend file if necessary */
+  void volatile **pp              /* OUT: Mapped memory */
 ){
   int rc = SQLITE_OK;
   TestvfsFile *pFd = (TestvfsFile *)pFile;
   Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);
 
-  if( p->pScript && p->mask&TESTVFS_SHMGET_MASK ){
+  if( p->pScript && p->mask&TESTVFS_SHMPAGE_MASK ){
-    tvfsExecTcl(p, "xShmGet", 
+    Tcl_Obj *pArg = Tcl_NewObj();
-        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 
+    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(iPage));
-        Tcl_NewIntObj(reqMapSize)
+    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(pgsz));
+    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(isWrite));
+    tvfsExecTcl(p, "xShmPage", 
+        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, pArg
     );
     tvfsResultCode(p, &rc);
   }
-  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMGET_MASK && tvfsInjectIoerr(p) ){
+  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMPAGE_MASK && tvfsInjectIoerr(p) ){
     rc = SQLITE_IOERR;
   }
 
-  *pMapSize = pFd->pShm->n;
+  if( rc==SQLITE_OK && isWrite && !pFd->pShm->aPage[iPage] ){
-  *pp = pFd->pShm->a;
+    tvfsAllocPage(pFd->pShm, iPage, pgsz);
-  return rc;
-}
-
-static int tvfsShmRelease(sqlite3_file *pFile){
-  int rc = SQLITE_OK;
-  TestvfsFile *pFd = (TestvfsFile *)pFile;
-  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);
-
-  if( p->pScript && p->mask&TESTVFS_SHMRELEASE_MASK ){
-    tvfsExecTcl(p, "xShmRelease", 
-        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
-    );
-    tvfsResultCode(p, &rc);
   }
+  *pp = (void volatile *)pFd->pShm->aPage[iPage];
 
   return rc;
 }
 
+
 static int tvfsShmLock(
   sqlite3_file *pFile,
   int ofst,
@@ -782,10 +778,13 @@ static int tvfsShmClose(
   *ppFd = pFd->pNext;
 
   if( pBuffer->pFile==0 ){
+    int i;
     TestvfsBuffer **pp;
     for(pp=&p->pBuffer; *pp!=pBuffer; pp=&((*pp)->pNext));
     *pp = (*pp)->pNext;
-    ckfree((char *)pBuffer->a);
+    for(i=0; pBuffer->aPage[i]; i++){
+      ckfree((char *)pBuffer->aPage[i]);
+    }
     ckfree((char *)pBuffer);
   }
   pFd->pShm = 0;
@@ -821,6 +820,8 @@ static int testvfs_obj_cmd(
 
   switch( (enum DB_enum)i ){
     case CMD_SHM: {
+      Tcl_Obj *pObj;
+      int i;
       TestvfsBuffer *pBuffer;
       char *zName;
       if( objc!=3 && objc!=4 ){
@@ -838,11 +839,22 @@ static int testvfs_obj_cmd(
       if( objc==4 ){
         int n;
         u8 *a = Tcl_GetByteArrayFromObj(objv[3], &n);
-        pBuffer->a = (u8 *)ckrealloc((char *)pBuffer->a, n);
+        assert( pBuffer->pgsz==0 || pBuffer->pgsz==32768 );
-        pBuffer->n = n;
+        for(i=0; i*32768<n; i++){
-        memcpy(pBuffer->a, a, n);
+          int nByte = 32768;
+          tvfsAllocPage(pBuffer, i, 32768);
+          if( n-i*32768<32768 ){
+            nByte = n;
           }
-      Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(pBuffer->a, pBuffer->n));
+          memcpy(pBuffer->aPage[i], &a[i*32768], nByte);
+        }
+      }
+
+      pObj = Tcl_NewObj();
+      for(i=0; pBuffer->aPage[i]; i++){
+        Tcl_AppendObjToObj(pObj, Tcl_NewByteArrayObj(pBuffer->aPage[i], 32768));
+      }
+      Tcl_SetObjResult(interp, pObj);
       break;
     }
 

src/wal.c

@@ -370,8 +370,8 @@ struct Wal {
   sqlite3_file *pDbFd;       /* File handle for the database file */
   sqlite3_file *pWalFd;      /* File handle for WAL file */
   u32 iCallback;             /* Value to pass to log callback (or 0) */
-  int szWIndex;              /* Size of the wal-index that is mapped in mem */
+  int nWiData;               /* Size of array apWiData */
-  volatile u32 *pWiData;     /* Pointer to wal-index content in memory */
+  volatile u32 **apWiData;   /* Pointer to wal-index content in memory */
   u16 szPage;                /* Database page size */
   i16 readLock;              /* Which read lock is being held.  -1 for none */
   u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
@@ -386,15 +386,77 @@ struct Wal {
 #endif
 };
 
+/*
+** Define the parameters of the hash tables in the wal-index file. There
+** is a hash-table following every HASHTABLE_NPAGE page numbers in the
+** wal-index.
+**
+** Changing any of these constants will alter the wal-index format and
+** create incompatibilities.
+*/
+#define HASHTABLE_NPAGE      4096  /* Must be power of 2 and multiple of 256 */
+#define HASHTABLE_DATATYPE   u16
+#define HASHTABLE_HASH_1     383                  /* Should be prime */
+#define HASHTABLE_NSLOT      (HASHTABLE_NPAGE*2)  /* Must be a power of 2 */
+#define HASHTABLE_NBYTE      (sizeof(HASHTABLE_DATATYPE)*HASHTABLE_NSLOT)
+
+/* The block of page numbers associated with the first hash-table in a
+** wal-index is smaller than usual. This is so that there is a complete
+** hash-table on each aligned 32KB page of the wal-index.
+*/
+#define HASHTABLE_NPAGE_ONE  (4096 - (WALINDEX_HDR_SIZE/sizeof(u32)))
+
+/* The wal-index is divided into pages of HASHTABLE_PAGESIZE bytes each. */
+#define HASHTABLE_PAGESIZE   (HASHTABLE_NBYTE + HASHTABLE_NPAGE*sizeof(u32))
+
+/*
+** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
+** is broken into pages of HASHTABLE_PAGESIZE bytes. Wal-index pages are
+** numbered from zero.
+**
+** If this call is successful, *ppPage is set to point to the wal-index
+** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs,
+** then an SQLite error code is returned and *ppPage is set to 0.
+*/
+static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
+  int rc = SQLITE_OK;
+
+  /* Enlarge the pWal->apWiData[] array if required */
+  if( pWal->nWiData<=iPage ){
+    int nByte = sizeof(u32 *)*(iPage+1);
+    volatile u32 **apNew;
+    apNew = (volatile u32 **)sqlite3_realloc(pWal->apWiData, nByte);
+    if( !apNew ){
+      *ppPage = 0;
+      return SQLITE_NOMEM;
+    }
+    memset(&apNew[pWal->nWiData], 0, sizeof(u32 *)*(iPage+1-pWal->nWiData));
+    pWal->apWiData = apNew;
+    pWal->nWiData = iPage+1;
+  }
+
+  /* Request a pointer to the required page from the VFS */
+  if( pWal->apWiData[iPage]==0 ){
+    rc = sqlite3OsShmPage(pWal->pDbFd, iPage, HASHTABLE_PAGESIZE, 
+        pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
+    );
+  }
+
+  *ppPage = pWal->apWiData[iPage];
+  assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
+  return rc;
+}
+
 /*
 ** Return a pointer to the WalCkptInfo structure in the wal-index.
 */
 static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
-  assert( pWal->pWiData!=0 );
+  volatile u32 *page1 = 0;
-  return (volatile WalCkptInfo*)&pWal->pWiData[sizeof(WalIndexHdr)/2];
+  walIndexPage(pWal, 0, &page1);
+  assert( page1 );
+  return (volatile WalCkptInfo*)&page1[sizeof(WalIndexHdr)/2];
 }
 
-
 /*
 ** This structure is used to implement an iterator that loops through
 ** all frames in the WAL in database page order. Where two or more frames
@@ -413,12 +475,13 @@ static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
 struct WalIterator {
   int iPrior;           /* Last result returned from the iterator */
   int nSegment;         /* Size of the aSegment[] array */
-  int nFinal;           /* Elements in aSegment[nSegment-1]  */
   struct WalSegment {
-    int iNext;              /* Next slot in aIndex[] not previously returned */
+    int iNext;                    /* Next slot in aIndex[] not yet returned */
-    u8 *aIndex;             /* i0, i1, i2... such that aPgno[iN] ascending */
+    HASHTABLE_DATATYPE *aIndex;   /* i0, i1, i2... such that aPgno[iN] ascend */
-    u32 *aPgno;             /* 256 page numbers.  Pointer to Wal.pWiData */
+    u32 *aPgno;                   /* Array of page numbers. */
-  } aSegment[1];        /* One for every 256 entries in the WAL */
+    int nEntry;                   /* Max size of aPgno[] and aIndex[] arrays */
+    int iZero;                    /* Frame number associated with aPgno[0] */
+  } aSegment[1];        /* One for every 32KB page in the WAL */
 };
 
 /*
@@ -492,7 +555,7 @@ static void walIndexWriteHdr(Wal *pWal){
   pWal->hdr.isInit = 1;
   walChecksumBytes(1, (u8*)&pWal->hdr, offsetof(WalIndexHdr, aCksum),
                    0, pWal->hdr.aCksum);
-  aHdr = (WalIndexHdr*)pWal->pWiData;
+  walIndexPage(pWal, 0, (volatile u32 **)&aHdr);
   memcpy(&aHdr[1], &pWal->hdr, sizeof(WalIndexHdr));
   sqlite3OsShmBarrier(pWal->pDbFd);
   memcpy(&aHdr[0], &pWal->hdr, sizeof(WalIndexHdr));
@@ -586,19 +649,6 @@ static int walDecodeFrame(
   return 1;
 }
 
-/*
-** Define the parameters of the hash tables in the wal-index file. There
-** is a hash-table following every HASHTABLE_NPAGE page numbers in the
-** wal-index.
-**
-** Changing any of these constants will alter the wal-index format and
-** create incompatibilities.
-*/
-#define HASHTABLE_NPAGE      4096  /* Must be power of 2 and multiple of 256 */
-#define HASHTABLE_DATATYPE   u16
-#define HASHTABLE_HASH_1     383                  /* Should be prime */
-#define HASHTABLE_NSLOT      (HASHTABLE_NPAGE*2)  /* Must be a power of 2 */
-#define HASHTABLE_NBYTE      (sizeof(HASHTABLE_DATATYPE)*HASHTABLE_NSLOT)
 
 #if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
 /*
@@ -663,96 +713,6 @@ static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
              walLockName(lockIdx), n));
 }
 
-/*
-** Return the index in the Wal.pWiData array that corresponds to 
-** frame iFrame.
-**
-** Wal.pWiData is an array of u32 elements that is the wal-index.
-** The array begins with a header and is then followed by alternating
-** "map" and "hash-table" blocks.  Each "map" block consists of
-** HASHTABLE_NPAGE u32 elements which are page numbers corresponding
-** to frames in the WAL file.  
-**
-** This routine returns an index X such that Wal.pWiData[X] is part
-** of a "map" block that contains the page number of the iFrame-th
-** frame in the WAL file.
-*/
-static int walIndexEntry(u32 iFrame){
-  return (
-      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)/sizeof(u32)
-    + (((iFrame-1)/HASHTABLE_NPAGE) * HASHTABLE_NBYTE)/sizeof(u32)
-    + (iFrame-1)
-  );
-}
-
-/*
-** Return the minimum size of the shared-memory, in bytes, that is needed
-** to support a wal-index containing frame iFrame.  The value returned
-** includes the wal-index header and the complete "block" containing iFrame,
-** including the hash table segment that follows the block.
-*/
-static int walMappingSize(u32 iFrame){
-  const int nByte = (sizeof(u32)*HASHTABLE_NPAGE + HASHTABLE_NBYTE) ;
-  return ( WALINDEX_LOCK_OFFSET 
-         + WALINDEX_LOCK_RESERVED 
-         + nByte * ((iFrame + HASHTABLE_NPAGE - 1)/HASHTABLE_NPAGE)
-  );
-}
-
-/*
-** Release our reference to the wal-index memory map, if we are holding
-** it.
-*/
-static void walIndexUnmap(Wal *pWal){
-  if( pWal->pWiData ){
-    sqlite3OsShmRelease(pWal->pDbFd);
-  }
-  pWal->pWiData = 0;
-  pWal->szWIndex = -1;
-}
-
-/*
-** Map the wal-index file into memory if it isn't already. 
-**
-** The reqSize parameter is the requested size of the mapping.  The
-** mapping will be at least this big if the underlying storage is
-** that big.  But the mapping will never grow larger than the underlying
-** storage.  Use the walIndexRemap() to enlarget the storage space.
-*/
-static int walIndexMap(Wal *pWal, int reqSize){
-  int rc = SQLITE_OK;
-  if( pWal->pWiData==0 || reqSize>pWal->szWIndex ){
-    walIndexUnmap(pWal);
-    rc = sqlite3OsShmGet(pWal->pDbFd, reqSize, &pWal->szWIndex,
-                             (void volatile**)(char volatile*)&pWal->pWiData);
-    if( rc!=SQLITE_OK ){
-      walIndexUnmap(pWal);
-    }
-  }
-  return rc;
-}
-
-/*
-** Enlarge the wal-index to be at least enlargeTo bytes in size and
-** Remap the wal-index so that the mapping covers the full size
-** of the underlying file.
-**
-** If enlargeTo is non-negative, then increase the size of the underlying
-** storage to be at least as big as enlargeTo before remapping.
-*/
-static int walIndexRemap(Wal *pWal, int enlargeTo){
-  int rc;
-  int sz;
-  assert( pWal->writeLock );
-  rc = sqlite3OsShmSize(pWal->pDbFd, enlargeTo, &sz);
-  if( rc==SQLITE_OK && sz>pWal->szWIndex ){
-    walIndexUnmap(pWal);
-    rc = walIndexMap(pWal, sz);
-  }
-  assert( pWal->szWIndex>=enlargeTo || rc!=SQLITE_OK );
-  return rc;
-}
-
 /*
 ** Compute a hash on a page number.  The resulting hash value must land
 ** between 0 and (HASHTABLE_NSLOT-1).  The walHashNext() function advances
@@ -767,6 +727,54 @@ static int walNextHash(int iPriorHash){
   return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
 }
 
+static void walHashGet(
+  Wal *pWal,                      /* WAL handle */
+  int iHash,                      /* Find the iHash'th table */
+  volatile HASHTABLE_DATATYPE **paHash,     /* OUT: Pointer to hash index */
+  volatile u32 **paPgno,          /* OUT: Pointer to page number array */
+  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
+){
+  u32 iZero;
+  volatile u32 *aPgno;
+  volatile HASHTABLE_DATATYPE *aHash;
+
+  walIndexPage(pWal, iHash, &aPgno);
+  aHash = (volatile HASHTABLE_DATATYPE *)&aPgno[HASHTABLE_NPAGE];
+
+  if( iHash==0 ){
+    aPgno = &aPgno[WALINDEX_HDR_SIZE/sizeof(u32)-1];
+    iZero = 0;
+  }else{
+    iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE;
+    aPgno = &aPgno[-1*iZero-1];
+  }
+
+  *paPgno = aPgno;
+  *paHash = aHash;
+  *piZero = iZero;
+}
+
+static int walFramePage(u32 iFrame){
+  int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE;
+  assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE)
+       && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE)
+       && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE))
+       && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)
+       && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE))
+  );
+  return iHash;
+}
+
+/*
+** Return the page number associated with frame iFrame in this WAL.
+*/
+static u32 walFramePgno(Wal *pWal, u32 iFrame){
+  int iHash = walFramePage(iFrame);
+  if( iHash==0 ){
+    return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
+  }
+  return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE];
+}
 
 /* 
 ** Find the hash table and (section of the) page number array used to
@@ -789,27 +797,8 @@ static void walHashFind(
   volatile u32 **paPgno,          /* OUT: Pointer to page number array */
   u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
 ){
-  u32 iZero;
+  int iHash = walFramePage(iFrame);
-  volatile u32 *aPgno;
+  walHashGet(pWal, iHash, paHash, paPgno, piZero);
-  volatile HASHTABLE_DATATYPE *aHash;
-
-  iZero = ((iFrame-1)/HASHTABLE_NPAGE) * HASHTABLE_NPAGE;
-  aPgno = &pWal->pWiData[walIndexEntry(iZero+1)-iZero-1];
-  aHash = (HASHTABLE_DATATYPE *)&aPgno[iZero+HASHTABLE_NPAGE+1];
-
-  /* Assert that:
-  **
-  **   + the mapping is large enough for this hash-table, and
-  **
-  **   + that aPgno[iZero+1] really is the database page number associated
-  **     with the first frame indexed by this hash table.
-  */
-  assert( (u32*)(&aHash[HASHTABLE_NSLOT])<=&pWal->pWiData[pWal->szWIndex/4] );
-  assert( walIndexEntry(iZero+1)==(&aPgno[iZero+1] - pWal->pWiData) );
-
-  *paHash = aHash;
-  *paPgno = aPgno;
-  *piZero = iZero;
 }
 
 /*
@@ -829,16 +818,16 @@ static void walCleanupHash(Wal *pWal){
   volatile u32 *aPgno;                 /* Unused return from walHashFind() */
   u32 iZero;                           /* frame == (aHash[x]+iZero) */
   int iLimit = 0;                      /* Zero values greater than this */
+  int nByte;                           /* Number of bytes to zero in aPgno[] */
+  int i;                               /* Used to iterate through aHash[] */
 
   assert( pWal->writeLock );
   testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE-1 );
   testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE );
   testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE+1 );
-  if( (pWal->hdr.mxFrame % HASHTABLE_NPAGE)>0 ){
-    int nByte;                    /* Number of bytes to zero in aPgno[] */
-    int i;                        /* Used to iterate through aHash[] */
 
   walHashFind(pWal, pWal->hdr.mxFrame+1, &aHash, &aPgno, &iZero);
+  if( iZero!=pWal->hdr.mxFrame ){
     iLimit = pWal->hdr.mxFrame - iZero;
     assert( iLimit>0 );
     for(i=0; i<HASHTABLE_NSLOT; i++){
@@ -850,9 +839,8 @@ static void walCleanupHash(Wal *pWal){
     /* Zero the entries in the aPgno array that correspond to frames with
     ** frame numbers greater than pWal->hdr.mxFrame. 
     */
-    nByte = sizeof(u32) * (HASHTABLE_NPAGE-iLimit);
+    nByte = ((char *)aHash - (char *)&aPgno[pWal->hdr.mxFrame+1]);
-    memset((void *)&aPgno[iZero+iLimit+1], 0, nByte);
+    memset((void *)&aPgno[pWal->hdr.mxFrame+1], 0, nByte);
-    assert( &((u8 *)&aPgno[iZero+iLimit+1])[nByte]==(u8 *)aHash );
   }
 
 #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
@@ -878,15 +866,7 @@ static void walCleanupHash(Wal *pWal){
 ** pPage into WAL frame iFrame.
 */
 static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
-  int rc;                         /* Return code */
+  int rc = SQLITE_OK;             /* Return code */
-  int nMapping;                   /* Required mapping size in bytes */
-  
-  /* Make sure the wal-index is mapped. Enlarge the mapping if required. */
-  nMapping = walMappingSize(iFrame);
-  rc = walIndexMap(pWal, nMapping);
-  while( rc==SQLITE_OK && nMapping>pWal->szWIndex ){
-    rc = walIndexRemap(pWal, nMapping);
-  }
 
   /* Assuming the wal-index file was successfully mapped, find the hash 
   ** table and section of of the page number array that pertain to frame 
@@ -904,8 +884,8 @@ static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
     walHashFind(pWal, iFrame, &aHash, &aPgno, &iZero);
     idx = iFrame - iZero;
     if( idx==1 ){
-      memset((void*)&aPgno[iZero+1], 0, HASHTABLE_NPAGE*sizeof(u32));
+      int nByte = (u8 *)&aHash[HASHTABLE_NSLOT] - (u8 *)&aPgno[1+iZero];
-      memset((void*)aHash, 0, HASHTABLE_NBYTE);
+      memset((void*)&aPgno[1+iZero], 0, nByte);
     }
     assert( idx <= HASHTABLE_NSLOT/2 + 1 );
 
@@ -1076,9 +1056,6 @@ static int walIndexRecover(Wal *pWal){
   }
 
 finished:
-  if( rc==SQLITE_OK && pWal->hdr.mxFrame==0 ){
-    rc = walIndexRemap(pWal, walMappingSize(1));
-  }
   if( rc==SQLITE_OK ){
     volatile WalCkptInfo *pInfo;
     int i;
@@ -1164,7 +1141,6 @@ int sqlite3WalOpen(
   pRet->pVfs = pVfs;
   pRet->pWalFd = (sqlite3_file *)&pRet[1];
   pRet->pDbFd = pDbFd;
-  pRet->szWIndex = -1;
   pRet->readLock = -1;
   sqlite3_randomness(8, &pRet->hdr.aSalt);
   pRet->zWalName = zWal = pVfs->szOsFile + (char*)pRet->pWalFd;
@@ -1207,24 +1183,22 @@ static int walIteratorNext(
   u32 iMin;                     /* Result pgno must be greater than iMin */
   u32 iRet = 0xFFFFFFFF;        /* 0xffffffff is never a valid page number */
   int i;                        /* For looping through segments */
-  int nBlock = p->nFinal;       /* Number of entries in current segment */
 
   iMin = p->iPrior;
   assert( iMin<0xffffffff );
   for(i=p->nSegment-1; i>=0; i--){
     struct WalSegment *pSegment = &p->aSegment[i];
-    while( pSegment->iNext<nBlock ){
+    while( pSegment->iNext<pSegment->nEntry ){
       u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
       if( iPg>iMin ){
         if( iPg<iRet ){
           iRet = iPg;
-          *piFrame = i*256 + 1 + pSegment->aIndex[pSegment->iNext];
+          *piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext];
         }
         break;
       }
       pSegment->iNext++;
     }
-    nBlock = 256;
   }
 
   *piPage = p->iPrior = iRet;
@@ -1232,28 +1206,28 @@ static int walIteratorNext(
 }
 
 
-static void walMergesort8(
+static void walMergesort(
-  Pgno *aContent,                 /* Pages in wal */
+  u32 *aContent,                  /* Pages in wal */
-  u8 *aBuffer,                    /* Buffer of at least *pnList items to use */
+  HASHTABLE_DATATYPE *aBuffer,    /* Buffer of at least *pnList items to use */
-  u8 *aList,                      /* IN/OUT: List to sort */
+  HASHTABLE_DATATYPE *aList,      /* IN/OUT: List to sort */
   int *pnList                     /* IN/OUT: Number of elements in aList[] */
 ){
   int nList = *pnList;
   if( nList>1 ){
     int nLeft = nList / 2;        /* Elements in left list */
     int nRight = nList - nLeft;   /* Elements in right list */
-    u8 *aLeft = aList;            /* Left list */
-    u8 *aRight = &aList[nLeft];   /* Right list */
     int iLeft = 0;                /* Current index in aLeft */
     int iRight = 0;               /* Current index in aright */
     int iOut = 0;                 /* Current index in output buffer */
+    HASHTABLE_DATATYPE *aLeft = aList;           /* Left list */
+    HASHTABLE_DATATYPE *aRight = &aList[nLeft];  /* Right list */
 
     /* TODO: Change to non-recursive version. */
-    walMergesort8(aContent, aBuffer, aLeft, &nLeft);
+    walMergesort(aContent, aBuffer, aLeft, &nLeft);
-    walMergesort8(aContent, aBuffer, aRight, &nRight);
+    walMergesort(aContent, aBuffer, aRight, &nRight);
 
     while( iRight<nRight || iLeft<nLeft ){
-      u8 logpage;
+      HASHTABLE_DATATYPE logpage;
       Pgno dbpage;
 
       if( (iLeft<nLeft) 
@@ -1300,60 +1274,68 @@ static void walMergesort8(
 ** prior to the WalIterator object being destroyed.
 */
 static int walIteratorInit(Wal *pWal, WalIterator **pp){
-  u32 *aData;           /* Content of the wal-index file */
   WalIterator *p;       /* Return value */
   int nSegment;         /* Number of segments to merge */
   u32 iLast;            /* Last frame in log */
   int nByte;            /* Number of bytes to allocate */
   int i;                /* Iterator variable */
-  int nFinal;           /* Number of unindexed entries */
+  HASHTABLE_DATATYPE *aTmp;       /* Temp space used by merge-sort */
-  u8 *aTmp;             /* Temp space used by merge-sort */
+  HASHTABLE_DATATYPE *aSpace;     /* Space at the end of the allocation */
-  u8 *aSpace;           /* Surplus space on the end of the allocation */
-
-  /* Make sure the wal-index is mapped into local memory */
-  assert( pWal->pWiData && pWal->szWIndex>=walMappingSize(pWal->hdr.mxFrame) );
 
   /* This routine only runs while holding SQLITE_SHM_CHECKPOINT.  No other
   ** thread is able to write to shared memory while this routine is
   ** running (or, indeed, while the WalIterator object exists).  Hence,
-  ** we can cast off the volatile qualifacation from shared memory
+  ** we can cast off the volatile qualification from shared memory
   */
   assert( pWal->ckptLock );
-  aData = (u32*)pWal->pWiData;
+  iLast = pWal->hdr.mxFrame;
 
   /* Allocate space for the WalIterator object */
-  iLast = pWal->hdr.mxFrame;
+  nSegment = walFramePage(iLast) + 1;
-  nSegment = (iLast >> 8) + 1;
+  nByte = sizeof(WalIterator) 
-  nFinal = (iLast & 0x000000FF);
+        + nSegment*(sizeof(struct WalSegment))
-  nByte = sizeof(WalIterator) + (nSegment+1)*(sizeof(struct WalSegment)+256);
+        + (nSegment+1)*(HASHTABLE_NPAGE * sizeof(HASHTABLE_DATATYPE));
   p = (WalIterator *)sqlite3_malloc(nByte);
   if( !p ){
     return SQLITE_NOMEM;
   }
   memset(p, 0, nByte);
 
-  /* Initialize the WalIterator object.  Each 256-entry segment is
+  /* Allocate space for the WalIterator object */
-  ** presorted in order to make iterating through all entries much
-  ** faster.
-  */
   p->nSegment = nSegment;
-  aSpace = (u8 *)&p->aSegment[nSegment];
+  aSpace = (HASHTABLE_DATATYPE *)&p->aSegment[nSegment];
-  aTmp = &aSpace[nSegment*256];
+  aTmp = &aSpace[HASHTABLE_NPAGE*nSegment];
   for(i=0; i<nSegment; i++){
+    volatile HASHTABLE_DATATYPE *pDummy;
     int j;
-    int nIndex = (i==nSegment-1) ? nFinal : 256;
+    u32 iZero;
-    p->aSegment[i].aPgno = &aData[walIndexEntry(i*256+1)];
+    int nEntry;
-    p->aSegment[i].aIndex = aSpace;
+    volatile u32 *aPgno;
-    for(j=0; j<nIndex; j++){
+
+    walHashGet(pWal, i, &pDummy, &aPgno, &iZero);
+    if( i==(nSegment-1) ){
+      nEntry = iLast - iZero;
+    }else if( i==0 ){
+      nEntry = HASHTABLE_NPAGE_ONE;
+    }else{
+      nEntry = HASHTABLE_NPAGE;
+    }
+    iZero++;
+    aPgno += iZero;
+
+    for(j=0; j<nEntry; j++){
       aSpace[j] = j;
     }
-    walMergesort8(p->aSegment[i].aPgno, aTmp, aSpace, &nIndex);
+    walMergesort((u32 *)aPgno, aTmp, aSpace, &nEntry);
-    memset(&aSpace[nIndex], aSpace[nIndex-1], 256-nIndex);
+    p->aSegment[i].iZero = iZero;
-    aSpace += 256;
+    p->aSegment[i].nEntry = nEntry;
-    p->nFinal = nIndex;
+    p->aSegment[i].aIndex = aSpace;
+    p->aSegment[i].aPgno = (u32 *)aPgno;
+    aSpace += HASHTABLE_NPAGE;
   }
+  assert( aSpace==aTmp );
 
-  /* Return the fully initializd WalIterator object */
+  /* Return the fully initialized WalIterator object */
   *pp = p;
   return SQLITE_OK ;
 }
@@ -1430,8 +1412,8 @@ static int walCheckpoint(
   ** cannot be backfilled from the WAL.
   */
   mxSafeFrame = pWal->hdr.mxFrame;
-  pHdr = (volatile WalIndexHdr*)pWal->pWiData;
+  walIndexPage(pWal, 0, (volatile u32 **)&pHdr);
-  pInfo = (volatile WalCkptInfo*)&pHdr[2];
+  pInfo = walCkptInfo(pWal);
   assert( pInfo==walCkptInfo(pWal) );
   for(i=1; i<WAL_NREADER; i++){
     u32 y = pInfo->aReadMark[i];
@@ -1461,6 +1443,7 @@ static int walCheckpoint(
 
     /* Iterate through the contents of the WAL, copying data to the db file. */
     while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
+      assert( walFramePgno(pWal, iFrame)==iDbpage );
       if( iFrame<=nBackfill || iFrame>mxSafeFrame ) continue;
       rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, 
           walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE
@@ -1525,7 +1508,6 @@ int sqlite3WalClose(
       if( rc==SQLITE_OK ){
         isDelete = 1;
       }
-      walIndexUnmap(pWal);
     }
 
     walIndexClose(pWal, isDelete);
@@ -1534,6 +1516,7 @@ int sqlite3WalClose(
       sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
     }
     WALTRACE(("WAL%p: closed\n", pWal));
+    sqlite3_free(pWal->apWiData);
     sqlite3_free(pWal);
   }
   return rc;
@@ -1560,13 +1543,14 @@ int walIndexTryHdr(Wal *pWal, int *pChanged){
   u32 aCksum[2];               /* Checksum on the header content */
   WalIndexHdr h1, h2;          /* Two copies of the header content */
   WalIndexHdr *aHdr;           /* Header in shared memory */
+  volatile u32 *page1 = 0;
 
-  if( pWal->szWIndex < WALINDEX_HDR_SIZE ){
+  walIndexPage(pWal, 0, &page1);
+  if( !page1 ){
     /* The wal-index is not large enough to hold the header, then assume
     ** header is invalid. */
     return 1;
   }
-  assert( pWal->pWiData );
 
   /* Read the header. This might happen currently with a write to the
   ** same area of shared memory on a different CPU in a SMP,
@@ -1578,7 +1562,7 @@ int walIndexTryHdr(Wal *pWal, int *pChanged){
   ** Memory barriers are used to prevent the compiler or the hardware from
   ** reordering the reads and writes.
   */
-  aHdr = (WalIndexHdr*)pWal->pWiData;
+  aHdr = (WalIndexHdr*)page1;
   memcpy(&h1, &aHdr[0], sizeof(h1));
   sqlite3OsShmBarrier(pWal->pDbFd);
   memcpy(&h2, &aHdr[1], sizeof(h2));
@@ -1625,9 +1609,10 @@ int walIndexTryHdr(Wal *pWal, int *pChanged){
 static int walIndexReadHdr(Wal *pWal, int *pChanged){
   int rc;                         /* Return code */
   int badHdr;                     /* True if a header read failed */
+  volatile u32 *dummy;
 
   assert( pChanged );
-  rc = walIndexMap(pWal, walMappingSize(1));
+  rc = walIndexPage(pWal, 0, &dummy);
   if( rc!=SQLITE_OK ){
     return rc;
   }
@@ -1659,14 +1644,6 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
     }
   }
 
-  /* Make sure the mapping is large enough to cover the entire wal-index */
-  if( rc==SQLITE_OK ){
-    int szWanted = walMappingSize(pWal->hdr.mxFrame);
-    if( pWal->szWIndex<szWanted ){
-      rc = walIndexMap(pWal, szWanted);
-    }
-  }
-
   return rc;
 }
 
@@ -1710,7 +1687,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
   u32 mxReadMark;                 /* Largest aReadMark[] value */
   int mxI;                        /* Index of largest aReadMark[] value */
   int i;                          /* Loop counter */
-  int rc;                         /* Return code  */
+  int rc = SQLITE_OK;             /* Return code  */
 
   assert( pWal->readLock<0 );     /* Not currently locked */
 
@@ -1739,16 +1716,14 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
         rc = SQLITE_BUSY_RECOVERY;
       }
     }
-  }else{
-    rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
   }
   if( rc!=SQLITE_OK ){
     return rc;
   }
 
-  pHdr = (volatile WalIndexHdr*)pWal->pWiData;
+  walIndexPage(pWal, 0, (volatile u32 **)&pHdr);
-  pInfo = (volatile WalCkptInfo*)&pHdr[2];
+  pInfo = walCkptInfo(pWal);
-  assert( pInfo==walCkptInfo(pWal) );
+  assert( pInfo==(volatile WalCkptInfo *)&pHdr[2] );
   if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
     /* The WAL has been completely backfilled (or it is empty).
     ** and can be safely ignored.
@@ -1883,7 +1858,6 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
   do{
     rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
   }while( rc==WAL_RETRY );
-  walIndexUnmap(pWal);
   return rc;
 }
 
@@ -1913,7 +1887,6 @@ int sqlite3WalRead(
   int nOut,                       /* Size of buffer pOut in bytes */
   u8 *pOut                        /* Buffer to write page data to */
 ){
-  int rc;                         /* Return code */
   u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
   u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
   int iHash;                      /* Used to loop through N hash tables */
@@ -1932,12 +1905,6 @@ int sqlite3WalRead(
     return SQLITE_OK;
   }
 
-  /* Ensure the wal-index is mapped. */
-  rc = walIndexMap(pWal, walMappingSize(iLast));
-  if( rc!=SQLITE_OK ){
-    return rc;
-  }
-
   /* Search the hash table or tables for an entry matching page number
   ** pgno. Each iteration of the following for() loop searches one
   ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
@@ -1963,16 +1930,13 @@ int sqlite3WalRead(
   **     This condition filters out entries that were added to the hash
   **     table after the current read-transaction had started.
   */
-  for(iHash=iLast; iHash>0 && iRead==0; iHash-=HASHTABLE_NPAGE){
+  for(iHash=walFramePage(iLast); iHash>=0 && iRead==0; iHash--){
     volatile HASHTABLE_DATATYPE *aHash;  /* Pointer to hash table */
     volatile u32 *aPgno;                 /* Pointer to array of page numbers */
     u32 iZero;                    /* Frame number corresponding to aPgno[0] */
     int iKey;                     /* Hash slot index */
-    int mxHash;                   /* upper bound on aHash[] values */
 
-    walHashFind(pWal, iHash, &aHash, &aPgno, &iZero);
+    walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
-    mxHash = iLast - iZero;
-    if( mxHash > HASHTABLE_NPAGE )  mxHash = HASHTABLE_NPAGE;
     for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
       u32 iFrame = aHash[iKey] + iZero;
       if( iFrame<=iLast && aPgno[iFrame]==pgno ){
@@ -1981,7 +1945,6 @@ int sqlite3WalRead(
       }
     }
   }
-  assert( iRead==0 || pWal->pWiData[walIndexEntry(iRead)]==pgno );
 
 #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
   /* If expensive assert() statements are available, do a linear search
@@ -1991,7 +1954,7 @@ int sqlite3WalRead(
     u32 iRead2 = 0;
     u32 iTest;
     for(iTest=iLast; iTest>0; iTest--){
-      if( pWal->pWiData[walIndexEntry(iTest)]==pgno ){
+      if( walFramePgno(pWal, iTest)==pgno ){
         iRead2 = iTest;
         break;
       }
@@ -2003,7 +1966,6 @@ int sqlite3WalRead(
   /* If iRead is non-zero, then it is the log frame number that contains the
   ** required page. Read and return data from the log file.
   */
-  walIndexUnmap(pWal);
   if( iRead ){
     i64 iOffset = walFrameOffset(iRead, pWal->hdr.szPage) + WAL_FRAME_HDRSIZE;
     *pInWal = 1;
@@ -2039,6 +2001,7 @@ void sqlite3WalDbsize(Wal *pWal, Pgno *pPgno){
 */
 int sqlite3WalBeginWriteTransaction(Wal *pWal){
   int rc;
+  volatile u32 *page1;
 
   /* Cannot start a write transaction without first holding a read
   ** transaction. */
@@ -2057,19 +2020,13 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
   ** time the read transaction on this connection was started, then
   ** the write is disallowed.
   */
-  rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
+  walIndexPage(pWal, 0, &page1);
-  if( rc ){
+  if( memcmp(&pWal->hdr, (void*)page1, sizeof(WalIndexHdr))!=0 ){
-    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
-    pWal->writeLock = 0;
-    return rc;
-  }
-  if( memcmp(&pWal->hdr, (void*)pWal->pWiData, sizeof(WalIndexHdr))!=0 ){
     walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
     pWal->writeLock = 0;
     rc = SQLITE_BUSY;
   }
 
-  walIndexUnmap(pWal);
   return rc;
 }
 
@@ -2102,11 +2059,7 @@ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
     Pgno iMax = pWal->hdr.mxFrame;
     Pgno iFrame;
   
-    assert( pWal->pWiData==0 );
     rc = walIndexReadHdr(pWal, &unused);
-    if( rc==SQLITE_OK ){
-      rc = walIndexMap(pWal, walMappingSize(iMax));
-    }
     if( rc==SQLITE_OK ){
       for(iFrame=pWal->hdr.mxFrame+1; 
           ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; 
@@ -2124,12 +2077,11 @@ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
         ** committed. As a result, the call to xUndo may not fail.
         */
         assert( pWal->writeLock );
-        assert( pWal->pWiData[walIndexEntry(iFrame)]!=1 );
+        assert( walFramePgno(pWal, iFrame)!=1 );
-        rc = xUndo(pUndoCtx, pWal->pWiData[walIndexEntry(iFrame)]);
+        rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
       }
       walCleanupHash(pWal);
     }
-    walIndexUnmap(pWal);
   }
   return rc;
 }
@@ -2170,7 +2122,6 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
   }
 
   if( aWalData[0]<pWal->hdr.mxFrame ){
-    rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
     pWal->hdr.mxFrame = aWalData[0];
     pWal->hdr.aFrameCksum[0] = aWalData[1];
     pWal->hdr.aFrameCksum[1] = aWalData[2];
@@ -2179,7 +2130,6 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
     }
   }
 
-  walIndexUnmap(pWal);
   return rc;
 }
 
@@ -2199,9 +2149,7 @@ static int walRestartLog(Wal *pWal){
   int rc = SQLITE_OK;
   int cnt;
 
-  if( pWal->readLock==0 
+  if( pWal->readLock==0 ){
-   && SQLITE_OK==(rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame)))
-  ){
     volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
     assert( pInfo->nBackfill==pWal->hdr.mxFrame );
     if( pInfo->nBackfill>0 ){
@@ -2237,11 +2185,6 @@ static int walRestartLog(Wal *pWal){
       int notUsed;
       rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
     }while( rc==WAL_RETRY );
-
-    /* Unmap the wal-index before returning. Otherwise the VFS layer may
-    ** hold a mutex for the duration of the IO performed by WalFrames().
-    */
-    walIndexUnmap(pWal);
   }
   return rc;
 }
@@ -2267,7 +2210,6 @@ int sqlite3WalFrames(
 
   assert( pList );
   assert( pWal->writeLock );
-  assert( pWal->pWiData==0 );
 
 #if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
   { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
@@ -2280,10 +2222,8 @@ int sqlite3WalFrames(
   ** log file, instead of appending to it at pWal->hdr.mxFrame.
   */
   if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){
-    assert( pWal->pWiData==0 );
     return rc;
   }
-  assert( pWal->pWiData==0 && pWal->readLock>0 );
 
   /* If this is the first frame written into the log, write the WAL
   ** header to the start of the WAL file. See comments at the top of
@@ -2358,7 +2298,6 @@ int sqlite3WalFrames(
 
     rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
   }
-  assert( pWal->pWiData==0 );
 
   /* Append data to the wal-index. It is not necessary to lock the 
   ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
@@ -2391,7 +2330,6 @@ int sqlite3WalFrames(
     }
   }
 
-  walIndexUnmap(pWal);
   WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
   return rc;
 }
@@ -2412,7 +2350,6 @@ int sqlite3WalCheckpoint(
   int rc;                         /* Return code */
   int isChanged = 0;              /* True if a new wal-index header is loaded */
 
-  assert( pWal->pWiData==0 );
   assert( pWal->ckptLock==0 );
 
   WALTRACE(("WAL%p: checkpoint begins\n", pWal));
@@ -2441,7 +2378,6 @@ int sqlite3WalCheckpoint(
   }
 
   /* Release the locks. */
-  walIndexUnmap(pWal);
   walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
   pWal->ckptLock = 0;
   WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));

test/permutations.test

@@ -13,6 +13,7 @@
 
 set testdir [file dirname $argv0]
 source $testdir/tester.tcl
+db close
 
 # Argument processing.
 #

test/wal2.test

@@ -75,9 +75,14 @@ proc incr_tvfs_hdr {file idx incrval} {
 #      database content.
 #
 do_test wal2-1.0 {
-  proc tvfs_cb {method args} { return SQLITE_OK }
+  proc tvfs_cb {method filename args} { 
+    set ::filename $filename
+    return SQLITE_OK 
+  }
+
   testvfs tvfs
   tvfs script tvfs_cb
+  tvfs filter xShmOpen
 
   sqlite3 db  test.db -vfs tvfs
   sqlite3 db2 test.db -vfs tvfs
@@ -123,21 +128,15 @@ foreach {tn iInsert res wal_index_hdr_mod wal_locks} "
 
   do_test wal2-1.$tn.1 {
     execsql { INSERT INTO t1 VALUES($iInsert) }
-
     set ::locks [list]
-    set ::cb_done 0
-
     proc tvfs_cb {method args} {
-      if {$::cb_done == 0 && $method == "xShmGet"} {
+      lappend ::locks [lindex $args 2]
-        set ::cb_done 1
-        if {$::wal_index_hdr_mod >= 0} {
-          incr_tvfs_hdr [lindex $args 0] $::wal_index_hdr_mod 1
-        }
-      }
-      if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
       return SQLITE_OK
     }
-
+    tvfs filter xShmLock
+    if {$::wal_index_hdr_mod >= 0} {
+      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
+    }
     execsql { SELECT count(a), sum(a) FROM t1 } db2
   } $res
 
@@ -174,8 +173,9 @@ do_test wal2-2.0 {
 
   testvfs tvfs
   tvfs script tvfs_cb
+  tvfs filter xShmOpen
   proc tvfs_cb {method args} {
-    if {$method == "xShmOpen"} { set ::shm_file [lindex $args 0] }
+    set ::filename [lindex $args 0]
     return SQLITE_OK
   }
 
@@ -208,32 +208,28 @@ foreach {tn iInsert res0 res1 wal_index_hdr_mod} {
          8   11   {10 55}  {11 66}   6
          9   12   {11 66}  {12 78}   7
 } {
+  tvfs filter xShmLock
+
   do_test wal2-2.$tn.1 {
-    set oldhdr [set_tvfs_hdr $::shm_file]
+    set oldhdr [set_tvfs_hdr $::filename]
     execsql { INSERT INTO t1 VALUES($iInsert) }
     execsql { SELECT count(a), sum(a) FROM t1 }
   } $res1
 
   do_test wal2-2.$tn.2 {
     set ::locks [list]
-    set ::cb_done 0
     proc tvfs_cb {method args} {
-      if {$::cb_done == 0 && $method == "xShmGet"} {
-        set ::cb_done 1
-        if {$::wal_index_hdr_mod >= 0} {
-          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
-        }
-      }
-      if {$method == "xShmLock"} {
       set lock [lindex $args 2]
       lappend ::locks $lock
       if {$lock == $::WRITER} {
-          set_tvfs_hdr $::shm_file $::oldhdr
+        set_tvfs_hdr $::filename $::oldhdr
-        }
       }
       return SQLITE_OK
     }
 
+    if {$::wal_index_hdr_mod >= 0} {
+      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
+    }
     execsql { SELECT count(a), sum(a) FROM t1 } db2
   } $res0
 
@@ -243,21 +239,15 @@ foreach {tn iInsert res0 res1 wal_index_hdr_mod} {
 
   do_test wal2-2.$tn.4 {
     set ::locks [list]
-    set ::cb_done 0
     proc tvfs_cb {method args} {
-      if {$::cb_done == 0 && $method == "xShmGet"} {
-        set ::cb_done 1
-        if {$::wal_index_hdr_mod >= 0} {
-          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
-        }
-      }
-      if {$method == "xShmLock"} {
       set lock [lindex $args 2]
       lappend ::locks $lock
-      }
       return SQLITE_OK
     }
 
+    if {$::wal_index_hdr_mod >= 0} {
+      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
+    }
     execsql { SELECT count(a), sum(a) FROM t1 } db2
   } $res1
 }

test/wal3.test

@@ -353,7 +353,7 @@ T script method_callback
 proc method_callback {method args} {
   if {$method == "xShmBarrier"} {
     incr ::barrier_count
-    if {$::barrier_count == 1} {
+    if {$::barrier_count == 2} {
       # This code is executed within the xShmBarrier() callback invoked
       # by the client running recovery as part of writing the recovered
       # wal-index header. If a second client attempts to access the