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Modify some comments in pager.c.

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FossilOrigin-Name: 5662da6d4f648e5d07d7cbea6bbd92fa684c02c9
This commit is contained in:
dan
2010-08-09 19:17:29 +00:00
parent 5a26383ab7
commit de5fd22f3d
3 changed files with 64 additions and 31 deletions
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81
src/pager.c
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@@ -241,6 +241,11 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
**
** WRITER_DBMOD:
**
** The pager transitions from WRITER_CACHEMOD into WRITER_DBMOD state
** when it modifies the contents of the database file. WAL connections
** never enter this state (since they do not modify the database file,
** just the log file).
**
** * A write transaction is active.
** * An EXCLUSIVE or greater lock is held on the database file.
** * The journal file is open and the first header has been written
@@ -250,6 +255,15 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
**
** WRITER_FINISHED:
**
** It is not possible for a WAL connection to enter this state.
**
** A rollback-mode pager changes to WRITER_FINISHED state from WRITER_DBMOD
** state after the entire transaction has been successfully written into the
** database file. In this state the transaction may be committed simply
** by finalizing the journal file. Once in WRITER_FINISHED state, it is
** not possible to modify the database further. At this point, the upper
** layer must either commit or rollback the transaction.
**
** * A write transaction is active.
** * An EXCLUSIVE or greater lock is held on the database file.
** * All writing and syncing of journal and database data has finished.
@@ -1642,17 +1656,29 @@ static int addToSavepointBitvecs(Pager *pPager, Pgno pgno){
}
/*
** Unlock the database file. This function is a no-op if the pager
** is in exclusive mode.
** This function is a no-op if the pager is in exclusive mode and not
** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
** state.
**
** If the pager is currently in error state, discard the contents of
** the cache and reset the Pager structure internal state. If there is
** an open journal-file, then the next time a shared-lock is obtained
** on the pager file (by this or any other process), it will be
** treated as a hot-journal and rolled back.
** If the pager is not in exclusive-access mode, the database file is
** completely unlocked. If the file is unlocked and the file-system does
** not exhibit the UNDELETABLE_WHEN_OPEN property, the journal file is
** closed (if it is open).
**
** If the pager is in ERROR state when this function is called, the
** contents of the pager cache are discarded before switching back to
** the OPEN state. Regardless of whether the pager is in exclusive-mode
** or not, any journal file left in the file-system will be treated
** as a hot-journal and rolled back the next time a read-transaction
** is opened (by this or by any other connection).
*/
static void pager_unlock(Pager *pPager){
assert( pPager->eState==PAGER_READER
|| pPager->eState==PAGER_OPEN
|| pPager->eState==PAGER_ERROR
);
sqlite3BitvecDestroy(pPager->pInJournal);
pPager->pInJournal = 0;
releaseAllSavepoints(pPager);
@@ -1719,18 +1745,20 @@ static void pager_unlock(Pager *pPager){
}
/*
** This function should be called when an IOERR, CORRUPT or FULL error
** may have occurred. The first argument is a pointer to the pager
** structure, the second the error-code about to be returned by a pager
** API function. The value returned is a copy of the second argument
** to this function.
** This function is called whenever an IOERR or FULL error that requires
** the pager to transition into the ERROR state may ahve occurred.
** The first argument is a pointer to the pager structure, the second
** the error-code about to be returned by a pager API function. The
** value returned is a copy of the second argument to this function.
**
** If the second argument is SQLITE_IOERR, SQLITE_CORRUPT, or SQLITE_FULL
** the error becomes persistent. Until the persistent error is cleared,
** subsequent API calls on this Pager will immediately return the same
** error code.
** If the second argument is SQLITE_FULL, SQLITE_IOERR or one of the
** IOERR sub-codes, the pager enters the ERROR state and the error code
** is stored in Pager.errCode. While the pager remains in the ERROR state,
** all major API calls on the Pager will immediately return Pager.errCode.
** Except, if the error-code is SQLITE_FULL, calls to PagerLookup() and
** PagerAcquire are handled as if the pager were in PAGER_READER state.
**
** A persistent error indicates that the contents of the pager-cache
** The ERROR state indicates that the contents of the pager-cache
** cannot be trusted. This state can be cleared by completely discarding
** the contents of the pager-cache. If a transaction was active when
** the persistent error occurred, then the rollback journal may need
@@ -2087,7 +2115,7 @@ static int pager_playback_one_page(
pagerReportSize(pPager);
}
/* If the pager is in RESERVED state, then there must be a copy of this
/* If the pager is in CACHEMOD state, then there must be a copy of this
** page in the pager cache. In this case just update the pager cache,
** not the database file. The page is left marked dirty in this case.
**
@@ -2098,8 +2126,11 @@ static int pager_playback_one_page(
** either. So the condition described in the above paragraph is not
** assert()able.
**
** If in EXCLUSIVE state, then we update the pager cache if it exists
** and the main file. The page is then marked not dirty.
** If in WRITER_DBMOD, WRITER_FINISHED or OPEN state, then we update the
** pager cache if it exists and the main file. The page is then marked
** not dirty. Since this code is only executed in PAGER_OPEN state for
** a hot-journal rollback, it is guaranteed that the page-cache is empty
** if the pager is in OPEN state.
**
** Ticket #1171: The statement journal might contain page content that is
** different from the page content at the start of the transaction.
@@ -2125,6 +2156,7 @@ static int pager_playback_one_page(
pPg = pager_lookup(pPager, pgno);
}
assert( pPg || !MEMDB );
assert( pPager->eState!=PAGER_OPEN || pPg==0 );
PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, (u8*)aData),
(isMainJrnl?"main-journal":"sub-journal")
@@ -2365,10 +2397,10 @@ delmaster_out:
** file in the file-system. This only happens when committing a transaction,
** or rolling back a transaction (including rolling back a hot-journal).
**
** If the main database file is not open, or an exclusive lock is not
** held, this function is a no-op. Otherwise, the size of the file is
** changed to nPage pages (nPage*pPager->pageSize bytes). If the file
** on disk is currently larger than nPage pages, then use the VFS
** If the main database file is not open, or the pager is not in either
** DBMOD or OPEN state, this function is a no-op. Otherwise, the size
** of the file is changed to nPage pages (nPage*pPager->pageSize bytes).
** If the file on disk is currently larger than nPage pages, then use the VFS
** xTruncate() method to truncate it.
**
** Or, it might might be the case that the file on disk is smaller than
@@ -2389,6 +2421,7 @@ static int pager_truncate(Pager *pPager, Pgno nPage){
&& (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)
){
i64 currentSize, newSize;
assert( pPager->eLock==EXCLUSIVE_LOCK );
/* TODO: Is it safe to use Pager.dbFileSize here? */
rc = sqlite3OsFileSize(pPager->fd, &currentSize);
newSize = pPager->pageSize*(i64)nPage;