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Add comments to clarify the purpose of the pager "error state".

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FossilOrigin-Name: fde4c59782e98366792e1552fd122e7d80a277ff
This commit is contained in:
dan
2010-08-03 15:57:09 +00:00
parent 937ac9da38
commit b22aa4a63d
3 changed files with 82 additions and 35 deletions
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12
manifest
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@@ -1,5 +1,5 @@
C Add\sstate\sdiagram\sto\scomments\sin\sexperimental\sversion\sof\spager.c.
D 2010-08-03T12:48:46
C Add\scomments\sto\sclarify\sthe\spurpose\sof\sthe\spager\s"error\sstate".
D 2010-08-03T15:57:10
F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
F Makefile.in ec08dc838fd8110fe24c92e5130bcd91cbb1ff2e
F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -156,7 +156,7 @@ F src/os_common.h a8f95b81eca8a1ab8593d23e94f8a35f35d4078f
F src/os_os2.c 72d0b2e562952a2464308c4ce5f7913ac10bef3e
F src/os_unix.c ae5ca8a6031380708f3fec7be325233d49944914
F src/os_win.c 51cb62f76262d961ea4249489383d714501315a7
F src/pager.c 24f978063ff3f18f1632b05b695717cc9818538a
F src/pager.c 809f4dfbca43fd64ef27855e193d8544a5054668
F src/pager.h 80726162dc3942f59ab27b738fb667b9ba0a89d5
F src/parse.y 12b7ebd61ea54f0e1b1083ff69cc2c8ce9353d58
F src/pcache.c 1e9aa2dbc0845b52e1b51cc39753b6d1e041cb07
@@ -841,7 +841,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
P 0a636798bdb6961a47327091715b254f79add823
R b916884b782901df5d25760d516d1243
P 16dcf5a6d3ebff9a734705693b5ac740f4ff2cc1
R f5f08ae2bf16feac4ddffb2e7526923b
U dan
Z a547af01cff05efb8820775070ecaafe
Z 158c2b787243a4910abe77703b2eb315

2
manifest.uuid
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@@ -1 +1 @@
16dcf5a6d3ebff9a734705693b5ac740f4ff2cc1
fde4c59782e98366792e1552fd122e7d80a277ff

99
src/pager.c
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@@ -140,6 +140,7 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
** * The dbSize, dbOrigSize and dbFileSize variables may not be trusted.
**
** READER:
**
** In this state all the requirements for reading the database in
** rollback (non-WAL) mode are met. Unless the pager is (or recently
** was) in exclusive-locking mode, a user-level read transaction is
@@ -152,12 +153,16 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
** may not be trusted at this point.
**
** WRITER_INITIAL:
**
** * A write transaction is active.
** * A RESERVED or greater lock is held on the database file.
** * The dbSize, dbOrigSize and dbFileSize variables are all valid.
** * The contents of the pager cache have not been modified.
** * The journal file may or may not be open.
** * Nothing (not even the first header) has been written to the journal.
**
** WRITER_CACHEMOD:
**
** * A write transaction is active.
** * A RESERVED or greater lock is held on the database file.
** * The journal file is open and the first header has been written
@@ -165,6 +170,7 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
** * The contents of the page cache have been modified.
**
** WRITER_DBMOD:
**
** * 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
@@ -173,6 +179,7 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
** written to disk).
**
** WRITER_FINISHED:
**
** * 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.
@@ -180,12 +187,62 @@ int sqlite3PagerTrace=1; /* True to enable tracing */
** commit the transaction. If an error did occur, the caller will need
** to rollback the transaction.
**
** ERROR:
**
** The ERROR state is entered when an IO, OOM or disk-full error
** occurs at a point in the code that makes it difficult to be sure
** that the in-memory pager state (cache contents, db size etc.) are
** consistent with the contents of the file-system.
**
** For example, if an IO error occurs while performing a rollback,
** the contents of the page-cache may be left in an inconsistent state.
** At this point it would be dangerous to change back to READER state
** (as usually happens after a rollback). Any subsequent readers might
** report database corruption (due to the inconsistent cache), and if
** they upgrade to writers, they may inadvertently corrupt the database
** file. To avoid this hazard, the pager switches into the ERROR state
** instead of READER following such an error.
**
** Once it has entered the ERROR state, any attempt to use the pager
** to read or write data returns an error. Eventually, once all
** outstanding transactions have been abandoned, the pager is able to
** transition back to NONE state, discarding the contents of the
** page-cache and any other in-memory state at the same time. Everything
** is reloaded from disk (and, if necessary, hot-journal rollback peformed)
** when a read-transaction is next opened on the pager (transitioning
** the pager into READER state). At that point the system has recovered
** from the error.
**
** Specifically, the pager jumps into the ERROR state if:
**
** 1. An error occurs while attempting a rollback. This happens in
** function sqlite3PagerRollback().
**
** 2. An error occurs while attempting to finalize a journal file
** following a commit in function sqlite3PagerCommitPhaseTwo().
**
** 3. An error occurs while attempting to write to the journal or
** database file in function pagerStress() in order to free up
** memory.
**
** In other cases, the error is returned to the b-tree layer. The b-tree
** layer then attempts a rollback operation. If the error condition
** persists, the pager enters the ERROR state via condition (1) above.
**
** Condition (3) is necessary because it can be triggered by a read-only
** statement executed within a transaction. In this case, if the error
** code were simply returned to the user, the b-tree layer would not
** automatically attempt a rollback, as it assumes that an error in a
** read-only statement cannot leave the pager in an internally inconsistent
** state.
**
**
** State diagram:
**
** NONE <-------------+
** | |
** V |
** +---------> READER------------->|
** NONE <------+------+
** | | |
** V | |
** +---------> READER-------+ |
** | | |
** | V |
** |<-------WRITER_INITIAL-----> ERROR
@@ -1619,7 +1676,6 @@ static int pager_end_transaction(Pager *pPager, int hasMaster){
|| (pPager->exclusiveMode && pPager->journalMode!=PAGER_JOURNALMODE_WAL)
){
rc = zeroJournalHdr(pPager, hasMaster);
pager_error(pPager, rc);
pPager->journalOff = 0;
}else{
/* This branch may be executed with Pager.journalMode==MEMORY if
@@ -4327,7 +4383,7 @@ int sqlite3PagerSharedLock(Pager *pPager){
rc = pager_wait_on_lock(pPager, SHARED_LOCK);
if( rc!=SQLITE_OK ){
assert( pPager->eLock==PAGER_UNLOCK );
return pager_error(pPager, rc);
goto failed;
}
}
@@ -4358,7 +4414,6 @@ int sqlite3PagerSharedLock(Pager *pPager){
*/
rc = pagerLock(pPager, EXCLUSIVE_LOCK);
if( rc!=SQLITE_OK ){
rc = pager_error(pPager, rc);
goto failed;
}
@@ -4411,6 +4466,10 @@ int sqlite3PagerSharedLock(Pager *pPager){
** it back since the process that crashed and left the hot journal
** probably did not sync it and we are required to always sync
** the journal before playing it back.
**
** Even if an error occurs while syncing or rolling back the
** hot-journal, there is no need to enter the ERROR state here, as
** the pager never left state NONE anyhow.
*/
if( isOpen(pPager->jfd) ){
rc = pagerSyncHotJournal(pPager);
@@ -4420,7 +4479,6 @@ int sqlite3PagerSharedLock(Pager *pPager){
pPager->eState = PAGER_NONE;
}
if( rc!=SQLITE_OK ){
rc = pager_error(pPager, rc);
goto failed;
}
}else{
@@ -4488,8 +4546,10 @@ int sqlite3PagerSharedLock(Pager *pPager){
failed:
if( rc!=SQLITE_OK ){
/* pager_unlock() is a no-op for exclusive mode and in-memory databases. */
pager_unlock(pPager);
assert( (pPager->eState==PAGER_NONE)
|| (pPager->exclusiveMode && pagerUseWal(pPager))
);
}else{
pPager->eState = PAGER_READER;
}
@@ -5544,21 +5604,12 @@ int sqlite3PagerCommitPhaseTwo(Pager *pPager){
** called, just return the same error code without doing anything. */
if( NEVER(pPager->errCode) ) return pPager->errCode;
/* This function should not be called if the pager is not in at least
** PAGER_RESERVED state. **FIXME**: Make it so that this test always
** fails - make it so that we never reach this point if we do not hold
** all necessary locks.
*/
assert( pPager->eState==PAGER_WRITER_INITIAL
|| pPager->eState==PAGER_WRITER_FINISHED
|| (pagerUseWal(pPager) && pPager->eState==PAGER_WRITER_CACHEMOD)
);
assert( assert_pager_state(pPager) );
#if 0
if( NEVER(pPager->state<PAGER_RESERVED) ) return SQLITE_ERROR;
#endif
/* An optimization. If the database was not actually modified during
** this transaction, the pager is running in exclusive-mode and is
** using persistent journals, then this function is a no-op.
@@ -5637,13 +5688,11 @@ int sqlite3PagerRollback(Pager *pPager){
if( pagerUseWal(pPager) ){
int rc2;
rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
rc2 = pager_end_transaction(pPager, pPager->setMaster);
if( rc==SQLITE_OK ) rc = rc2;
rc = pager_error(pPager, rc);
}else if( pPager->eState==PAGER_WRITER_INITIAL ){
rc = pager_end_transaction(pPager, pPager->setMaster);
rc = pager_end_transaction(pPager, 0);
}else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
if( pPager->eState>=PAGER_WRITER_DBMOD ){
pager_playback(pPager, 0);
@@ -5660,14 +5709,12 @@ int sqlite3PagerRollback(Pager *pPager){
}else{
rc = pager_playback(pPager, 0);
}
}
/* If an error occurs during a ROLLBACK, we can no longer trust the pager
** cache. So call pager_error() on the way out to make any error
** persistent.
** cache. So call pager_error() on the way out to make any error persistent.
*/
rc = pager_error(pPager, rc);
}
return rc;
return pager_error(pPager, rc);
}
/*