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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.

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FossilOrigin-Name: ad78ccacb00e2f8a5ca93e2c9006266d9477fe48
This commit is contained in:
dan
2010-07-30 11:31:12 +00:00
parent abfb62f9bd
commit 1e01cf1b84
3 changed files with 34 additions and 34 deletions
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42
src/pager.c
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@@ -282,11 +282,9 @@ struct PagerSavepoint {
**
** journalStarted
**
** This flag is set whenever the the main journal is opened and
** initialized
** This flag is set during a write-transaction after the first
** 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
** (if any) is only written into the journal file once.
** When PagerCommitPhaseOne() is called to commit a transaction, it may
** (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)
** may be written into the journal file while the pager is still in
** PAGER_RESERVED state (see CommitPhaseOne() for the action). It
** then attempts to upgrade to an exclusive lock. If this attempt
** fails, then SQLITE_BUSY may be returned to the user and the user
** may attempt to commit the transaction again later (calling
** CommitPhaseOne() again). This flag is used to ensure that the
** master journal name is only written to the journal file the first
** time CommitPhaseOne() is called.
** Whether or not a journal file contains a master-journal pointer affects
** the way in which the journal file is finalized after the transaction is
** committed or rolled back when running in "journal_mode=PERSIST" mode.
** If a journal file does not contain a master-journal pointer, it is
** finalized by overwriting the first journal header with zeroes. If,
** on the other hand, it does contain a master-journal pointer, the
** journal file is finalized by truncating it to zero bytes, just as if
** the connection were running in "journal_mode=truncate" mode.
**
** 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
){