Experimental "PRAGMA data_version" command for detecting when another process

has changed the database file.

FossilOrigin-Name: 43db1f44bce5a0ee50197b95ab0d844540b69d86

manifest

@@ -1,5 +1,5 @@
-C Simplify\sthe\simplementation\sof\sthe\s"header-value"\spragmas\s(schema_version,\nuser_version,\sfreelist_count,\sand\sapplication_id)\sby\smaking\sthem\smore\ntable-driven.
-D 2014-12-19T18:49:55.326
+C Experimental\s"PRAGMA\sdata_version"\scommand\sfor\sdetecting\swhen\sanother\sprocess\nhas\schanged\sthe\sdatabase\sfile.
+D 2014-12-19T19:28:02.465
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 6c4f961fa91d0b4fa121946a19f9e5eac2f2f809
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -173,8 +173,8 @@ F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
 F src/backup.c 7ddee9c7d505e07e959a575b18498f17c71e53ea
 F src/bitvec.c 19a4ba637bd85f8f63fc8c9bae5ade9fb05ec1cb
 F src/btmutex.c 49ca66250c7dfa844a4d4cb8272b87420d27d3a5
-F src/btree.c 92f745ccd18099973beb28e25fce80148545429e
-F src/btree.h e31a3a3ebdedb1caf9bda3ad5dbab3db9b780f6e
+F src/btree.c b2b2bd0aa02430fe86bc891295db919fcafb0d64
+F src/btree.h 94277c1d30c0b75705974bcc8b0c05e79c03d474
 F src/btreeInt.h 3363e18fd76f69a27a870b25221b2345b3fd4d21
 F src/build.c 162d84e4833b03f9d07192ef06057b0226f6e543
 F src/callback.c 7b44ce59674338ad48b0e84e7b72f935ea4f68b0
@@ -216,13 +216,13 @@ F src/os_setup.h c9d4553b5aaa6f73391448b265b89bed0b890faa
 F src/os_unix.c fb587121840f690101336879adfa6d0b2cd0e8c7
 F src/os_win.c ecb04a0dad2fa6fa659931a9d8f0f3aca33f908a
 F src/os_win.h 09e751b20bbc107ffbd46e13555dc73576d88e21
-F src/pager.c 7a5c5bc0e29b9b16834f5558a9d5d22bbae59a08
-F src/pager.h d1eee3c3f741be247ce6d82752a178515fc8578b
+F src/pager.c abe022cd72e112a05db5fd1d6d46f5ed93284247
+F src/pager.h c3476e7c89cdf1c6914e50a11f3714e30b4e0a77
 F src/parse.y 5dfead8aed90cb0c7c1115898ee2266804daff45
 F src/pcache.c ace1b67632deeaa84859b4c16c27711dfb7db3d4
 F src/pcache.h b44658c9c932d203510279439d891a2a83e12ba8
 F src/pcache1.c facbdd3ecc09c8f750089d941305694301328e98
-F src/pragma.c 7337e5d9f14664e987be3e6ed4d73fad16e48ad1
+F src/pragma.c bd33aa24456f043bb6f6d32a918bbeed41d8c591
 F src/prepare.c 173a5a499138451b2561614ecb87d78f9f4644b9
 F src/printf.c 9e75a6a0b55bf61cfff7d7e19d89834a1b938236
 F src/random.c ba2679f80ec82c4190062d756f22d0c358180696
@@ -1197,7 +1197,7 @@ F tool/logest.c eef612f8adf4d0993dafed0416064cf50d5d33c6
 F tool/mkautoconfamal.sh 5dc5010e2e748a9e1bba67baca5956a2c2deda7b
 F tool/mkkeywordhash.c dfff09dbbfaf950e89af294f48f902181b144670
 F tool/mkopts.tcl 66ac10d240cc6e86abd37dc908d50382f84ff46e
-F tool/mkpragmatab.tcl f7facbe8988ce61946f8069d34827ffc6af92521
+F tool/mkpragmatab.tcl 07a5124cf2dbafa1b375eefcf8ac4227028b0f8b
 F tool/mkspeedsql.tcl a1a334d288f7adfe6e996f2e712becf076745c97
 F tool/mksqlite3c-noext.tcl 88a1e3b0c769773fb7a9ebb363ffc603a4ac21d8
 F tool/mksqlite3c.tcl e72c0c97fe1a105fa9616483e652949be2199fe6
@@ -1233,7 +1233,10 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 8c5dd6cc259e0cdaaddaa52ccfa96fee6b166906
-R 8ba8633e296b4b7fe64ae8b30f249024
+P da27a09d1d991583b59997f6cc67efa28ffd9d6a
+R df4854633d0919cb180185852b6a45b5
+T *branch * data_version_pragma
+T *sym-data_version_pragma *
+T -sym-trunk *
 U drh
-Z d788c0d876adfa7410350841952e3917
+Z 81defb06f28b03737e8cb7607139b4d9

manifest.uuid

@@ -1 +1 @@
-da27a09d1d991583b59997f6cc67efa28ffd9d6a
+43db1f44bce5a0ee50197b95ab0d844540b69d86

src/btree.c

@@ -8177,6 +8177,13 @@ int sqlite3BtreeDropTable(Btree *p, int iTable, int *piMoved){
 ** The schema layer numbers meta values differently.  At the schema
 ** layer (and the SetCookie and ReadCookie opcodes) the number of
 ** free pages is not visible.  So Cookie[0] is the same as Meta[1].
+**
+** This routine treats Meta[BTREE_DATA_VERSION] as a special case.  Instead
+** of reading the value out of the header, it instead loads the "DataVersion"
+** from the pager.  The BTREE_DATA_VERSION value is not actually stored in the
+** database file.  It is a number computed by the pager.  But its access
+** pattern is the same as header meta values, and so it is convenient to
+** read it from this routine.
 */
 void sqlite3BtreeGetMeta(Btree *p, int idx, u32 *pMeta){
   BtShared *pBt = p->pBt;
@@ -8187,7 +8194,11 @@ void sqlite3BtreeGetMeta(Btree *p, int idx, u32 *pMeta){
   assert( pBt->pPage1 );
   assert( idx>=0 && idx<=15 );
 
+  if( idx==BTREE_DATA_VERSION ){
+    *pMeta = sqlite3PagerDataVersion(pBt->pPager);
+  }else{
     *pMeta = get4byte(&pBt->pPage1->aData[36 + idx*4]);
+  }
 
   /* If auto-vacuum is disabled in this build and this is an auto-vacuum
   ** database, mark the database as read-only.  */

src/btree.h

@@ -19,7 +19,7 @@
 /* TODO: This definition is just included so other modules compile. It
 ** needs to be revisited.
 */
-#define SQLITE_N_BTREE_META 10
+#define SQLITE_N_BTREE_META 16
 
 /*
 ** If defined as non-zero, auto-vacuum is enabled by default. Otherwise
@@ -134,6 +134,11 @@ int sqlite3BtreeNewDb(Btree *p);
 ** For example, the free-page-count field is located at byte offset 36 of
 ** the database file header. The incr-vacuum-flag field is located at
 ** byte offset 64 (== 36+4*7).
+**
+** The BTREE_DATA_VERSION value is not really a value stored in the header.
+** It is a read-only number computed by the pager.  But we merge it with
+** the header value access routines since its access pattern is the same.
+** Call it a "virtual meta value".
 */
 #define BTREE_FREE_PAGE_COUNT     0
 #define BTREE_SCHEMA_VERSION      1
@@ -144,6 +149,7 @@ int sqlite3BtreeNewDb(Btree *p);
 #define BTREE_USER_VERSION        6
 #define BTREE_INCR_VACUUM         7
 #define BTREE_APPLICATION_ID      8
+#define BTREE_DATA_VERSION        15  /* A virtual meta-value */
 
 /*
 ** Values that may be OR'd together to form the second argument of an

src/pager.c

@@ -646,6 +646,7 @@ struct Pager {
   u8 setMaster;               /* True if a m-j name has been written to jrnl */
   u8 doNotSpill;              /* Do not spill the cache when non-zero */
   u8 subjInMemory;            /* True to use in-memory sub-journals */
+  u8 bUseFetch;               /* True to use xFetch() */
   Pgno dbSize;                /* Number of pages in the database */
   Pgno dbOrigSize;            /* dbSize before the current transaction */
   Pgno dbFileSize;            /* Number of pages in the database file */
@@ -663,9 +664,9 @@ struct Pager {
   sqlite3_backup *pBackup;    /* Pointer to list of ongoing backup processes */
   PagerSavepoint *aSavepoint; /* Array of active savepoints */
   int nSavepoint;             /* Number of elements in aSavepoint[] */
+  u32 nReset;                 /* Number of calls to pager_reset() */
   char dbFileVers[16];        /* Changes whenever database file changes */
 
-  u8 bUseFetch;               /* True to use xFetch() */
   int nMmapOut;               /* Number of mmap pages currently outstanding */
   sqlite3_int64 szMmap;       /* Desired maximum mmap size */
   PgHdr *pMmapFreelist;       /* List of free mmap page headers (pDirty) */
@@ -1681,10 +1682,19 @@ static int writeMasterJournal(Pager *pPager, const char *zMaster){
 ** Discard the entire contents of the in-memory page-cache.
 */
 static void pager_reset(Pager *pPager){
+  pPager->nReset++;
   sqlite3BackupRestart(pPager->pBackup);
   sqlite3PcacheClear(pPager->pPCache);
 }
 
+/*
+** Return the pPager->nReset value
+*/
+u32 sqlite3PagerDataVersion(Pager *pPager){
+  assert( pPager->eState>PAGER_OPEN );
+  return pPager->nReset;
+}
+
 /*
 ** Free all structures in the Pager.aSavepoint[] array and set both
 ** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal

src/pager.h

@@ -172,6 +172,7 @@ int sqlite3PagerSharedLock(Pager *pPager);
 
 /* Functions used to query pager state and configuration. */
 u8 sqlite3PagerIsreadonly(Pager*);
+u32 sqlite3PagerDataVersion(Pager*);
 int sqlite3PagerRefcount(Pager*);
 int sqlite3PagerMemUsed(Pager*);
 const char *sqlite3PagerFilename(Pager*, int);

src/pragma.c

@@ -154,6 +154,12 @@ static const struct sPragmaNames {
     /* ePragFlag: */ 0,
     /* iArg:      */ 0 },
 #endif
+#if !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
+  { /* zName:     */ "data_version",
+    /* ePragTyp:  */ PragTyp_HEADER_VALUE,
+    /* ePragFlag: */ PragFlag_ReadOnly,
+    /* iArg:      */ BTREE_DATA_VERSION },
+#endif
 #if !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)
   { /* zName:     */ "database_list",
     /* ePragTyp:  */ PragTyp_DATABASE_LIST,
@@ -471,7 +477,7 @@ static const struct sPragmaNames {
     /* iArg:      */ SQLITE_WriteSchema|SQLITE_RecoveryMode },
 #endif
 };
-/* Number of pragmas: 57 on by default, 70 total. */
+/* Number of pragmas: 58 on by default, 71 total. */
 /* End of the automatically generated pragma table.
 ***************************************************************************/
 

tool/mkpragmatab.tcl

@@ -254,6 +254,12 @@ set pragma_def {
   ARG:  BTREE_USER_VERSION
   IF:   !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
 
+  NAME: data_version
+  TYPE: HEADER_VALUE
+  ARG:  BTREE_DATA_VERSION
+  FLAG: ReadOnly
+  IF:   !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
+
   NAME: freelist_count
   TYPE: HEADER_VALUE
   ARG:  BTREE_FREE_PAGE_COUNT