Add the SQLITE_FCNTL_OVERWRITE file-control. Used by SQLite to indicate to the OS layer that the current transaction will overwrite the entire file.

FossilOrigin-Name: 1da87fcdacfa7d277c3ee98e410a9ea8b529c368

3 files changed, 20 insertions, 8 deletions

diff --git a/src/backup.c b/src/backup.c
index 70a782665..411a9b8d6 100644
--- a/src/backup.c
+++ b/src/backup.c
@@ -669,10 +669,18 @@ void sqlite3BackupRestart(sqlite3_backup *pBackup){
 */
 int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){
   int rc;
+  sqlite3_file *pFd;              /* File descriptor for database pTo */
   sqlite3_backup b;
   sqlite3BtreeEnter(pTo);
   sqlite3BtreeEnter(pFrom);
 
+  assert( sqlite3BtreeIsInTrans(pTo) );
+  pFd = sqlite3PagerFile(sqlite3BtreePager(pTo));
+  if( pFd->pMethods ){
+    i64 nByte = sqlite3BtreeGetPageSize(pFrom)*(i64)sqlite3BtreeLastPage(pFrom);
+    sqlite3OsFileControl(pFd, SQLITE_FCNTL_OVERWRITE, &nByte);
+  }
+
   /* Set up an sqlite3_backup object. sqlite3_backup.pDestDb must be set
   ** to 0. This is used by the implementations of sqlite3_backup_step()
   ** and sqlite3_backup_finish() to detect that they are being called
@@ -698,6 +706,7 @@ int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){
     pTo->pBt->pageSizeFixed = 0;
   }
 
+  assert( sqlite3BtreeIsInTrans(pTo)==0 );
   sqlite3BtreeLeave(pFrom);
   sqlite3BtreeLeave(pTo);
   return rc;
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index d13f17639..040c365d8 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -766,7 +766,11 @@ struct sqlite3_io_methods {
 ** That integer is 0 to disable persistent WAL mode or 1 to enable persistent
 ** WAL mode.  If the integer is -1, then it is overwritten with the current
 ** WAL persistence setting.
-** 
+**
+** ^The [SQLITE_FCNTL_OVERWRITE] opcode is invoked by SQLite after opening
+** a write transaction to indicate that, unless it is rolled back for some
+** reason, the entire database file will be overwritten by the current 
+** transaction. This is used by VACUUM operations.
 */
 #define SQLITE_FCNTL_LOCKSTATE        1
 #define SQLITE_GET_LOCKPROXYFILE      2
@@ -778,6 +782,7 @@ struct sqlite3_io_methods {
 #define SQLITE_FCNTL_SYNC_OMITTED     8
 #define SQLITE_FCNTL_WIN32_AV_RETRY   9
 #define SQLITE_FCNTL_PERSIST_WAL     10
+#define SQLITE_FCNTL_OVERWRITE       11
 
 /*
 ** CAPI3REF: Mutex Handle
diff --git a/src/vacuum.c b/src/vacuum.c
index 0e92f4fb0..58a3c9d68 100644
--- a/src/vacuum.c
+++ b/src/vacuum.c
@@ -263,13 +263,11 @@ int sqlite3RunVacuum(char **pzErrMsg, sqlite3 *db){
   );
   if( rc ) goto end_of_vacuum;
 
-  /* At this point, unless the main db was completely empty, there is now a
-  ** transaction open on the vacuum database, but not on the main database.
-  ** Open a btree level transaction on the main database. This allows a
-  ** call to sqlite3BtreeCopyFile(). The main database btree level
-  ** transaction is then committed, so the SQL level never knows it was
-  ** opened for writing. This way, the SQL transaction used to create the
-  ** temporary database never needs to be committed.
+  /* At this point, there is a write transaction open on both the 
+  ** vacuum database and the main database. Assuming no error occurs,
+  ** both transactions are closed by this block - the main database
+  ** transaction by sqlite3BtreeCopyFile() and the other by an explicit
+  ** call to sqlite3BtreeCommit().
   */
   {
     u32 meta;