Changes to the comments describing the Pager.setMaster variable in pager.c. Add an assert() statement to verify that two master journal pointers are not written to a single journal file.

FossilOrigin-Name: ad78ccacb00e2f8a5ca93e2c9006266d9477fe48

manifest

@@ -1,8 +1,5 @@
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+C Changes\sto\sthe\scomments\sdescribing\sthe\sPager.setMaster\svariable\sin\spager.c.\sAdd\san\sassert()\sstatement\sto\sverify\sthat\stwo\smaster\sjournal\spointers\sare\snot\swritten\sto\sa\ssingle\sjournal\sfile.
-Hash: SHA1
+D 2010-07-30T11:31:13
-
-C Cherry-pick\sthe\smulti-file\stransaction\sfix\sfor\sticket\s[f3e5abed55]\sout\sof\nthe\sexperimental\sbranch.
-D 2010-07-30T11:20:36
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 F Makefile.in ec08dc838fd8110fe24c92e5130bcd91cbb1ff2e
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -159,7 +156,7 @@ F src/os_common.h a8f95b81eca8a1ab8593d23e94f8a35f35d4078f
 F src/os_os2.c 72d0b2e562952a2464308c4ce5f7913ac10bef3e
 F src/os_unix.c 3109e0e5a0d5551bab2e8c7322b20a3b8b171248
 F src/os_win.c 1f8b0a1a5bcf6289e7754d0d3c16cec16d4c93ab
-F src/pager.c d559cc0bb784fe5f5b812b2bc2329f09231515a5
+F src/pager.c 3f2373792cb5c23043cef31878a13b37b0ade1f6
 F src/pager.h 80726162dc3942f59ab27b738fb667b9ba0a89d5
 F src/parse.y 12b7ebd61ea54f0e1b1083ff69cc2c8ce9353d58
 F src/pcache.c 1e9aa2dbc0845b52e1b51cc39753b6d1e041cb07
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 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
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manifest.uuid

@@ -1 +1 @@
-40f7f0a583e6bba66cd006253a0ef4623ea74f17
+ad78ccacb00e2f8a5ca93e2c9006266d9477fe48

src/pager.c

@@ -282,11 +282,9 @@ struct PagerSavepoint {
 **
 ** journalStarted
 **
-**   This flag is set whenever the the main journal is opened and
+**   This flag is set during a write-transaction after the first 
-**   initialized
+**   journal-header is written and synced to disk.
 **
-**   The point of this flag is that it must be set after the 
-**   first journal header in a journal file has been synced to disk.
 **   After this has happened, new pages appended to the database 
 **   do not need the PGHDR_NEED_SYNC flag set, as they do not need
 **   to wait for a journal sync before they can be written out to
@@ -294,18 +292,28 @@ struct PagerSavepoint {
 **   
 ** setMaster
 **
-**   This variable is used to ensure that the master journal file name
+**   When PagerCommitPhaseOne() is called to commit a transaction, it may
-**   (if any) is only written into the journal file once.
+**   (or may not) specify a master-journal name to be written into the 
+**   journal file before it is synced to disk.
 **
-**   When committing a transaction, the master journal file name (if any)
+**   Whether or not a journal file contains a master-journal pointer affects 
-**   may be written into the journal file while the pager is still in
+**   the way in which the journal file is finalized after the transaction is 
-**   PAGER_RESERVED state (see CommitPhaseOne() for the action). It
+**   committed or rolled back when running in "journal_mode=PERSIST" mode.
-**   then attempts to upgrade to an exclusive lock. If this attempt
+**   If a journal file does not contain a master-journal pointer, it is
-**   fails, then SQLITE_BUSY may be returned to the user and the user
+**   finalized by overwriting the first journal header with zeroes. If,
-**   may attempt to commit the transaction again later (calling
+**   on the other hand, it does contain a master-journal pointer, the
-**   CommitPhaseOne() again). This flag is used to ensure that the 
+**   journal file is finalized by truncating it to zero bytes, just as if
-**   master journal name is only written to the journal file the first
+**   the connection were running in "journal_mode=truncate" mode.
-**   time CommitPhaseOne() is called.
+**
+**   Journal files that contain master journal pointers cannot be finalized
+**   simply by overwriting the first journal-header with zeroes, as the
+**   master journal pointer could interfere with hot-journal rollback of any
+**   subsequently interrupted transaction that reuses the journal file.
+**
+**   The flag is cleared as soon as the journal file is finalized (either
+**   by PagerCommitPhaseTwo or PagerRollback). If an IO error prevents the
+**   journal file from being successfully finalized, the setMaster flag
+**   is cleared anyway.
 **
 ** doNotSpill, doNotSyncSpill
 **
@@ -1073,7 +1081,9 @@ static int writeMasterJournal(Pager *pPager, const char *zMaster){
   i64 jrnlSize;                    /* Size of journal file on disk */
   u32 cksum = 0;                   /* Checksum of string zMaster */
 
-  if( !zMaster || pPager->setMaster
+  assert( pPager->setMaster==0 );
+
+  if( !zMaster 
    || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
    || pPager->journalMode==PAGER_JOURNALMODE_OFF 
   ){