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/*
** 2001 September 15
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** This is the implementation of the page cache subsystem or "pager".
**
** The pager is used to access a database disk file. It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file. The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "wal.h"
/******************* NOTES ON THE DESIGN OF THE PAGER ************************
**
** This comment block describes invariants that hold when using a rollback
** journal. These invariants do not apply for journal_mode=WAL,
** journal_mode=MEMORY, or journal_mode=OFF.
**
** Within this comment block, a page is deemed to have been synced
** automatically as soon as it is written when PRAGMA synchronous=OFF.
** Otherwise, the page is not synced until the xSync method of the VFS
** is called successfully on the file containing the page.
**
** Definition: A page of the database file is said to be "overwriteable" if
** one or more of the following are true about the page:
**
** (a) The original content of the page as it was at the beginning of
** the transaction has been written into the rollback journal and
** synced.
**
** (b) The page was a freelist leaf page at the start of the transaction.
**
** (c) The page number is greater than the largest page that existed in
** the database file at the start of the transaction.
**
** (1) A page of the database file is never overwritten unless one of the
** following are true:
**
** (a) The page and all other pages on the same sector are overwriteable.
**
** (b) The atomic page write optimization is enabled, and the entire
** transaction other than the update of the transaction sequence
** number consists of a single page change.
**
** (2) The content of a page written into the rollback journal exactly matches
** both the content in the database when the rollback journal was written
** and the content in the database at the beginning of the current
** transaction.
**
** (3) Writes to the database file are an integer multiple of the page size
** in length and are aligned on a page boundary.
**
** (4) Reads from the database file are either aligned on a page boundary and
** an integer multiple of the page size in length or are taken from the
** first 100 bytes of the database file.
**
** (5) All writes to the database file are synced prior to the rollback journal
** being deleted, truncated, or zeroed.
**
** (6) If a master journal file is used, then all writes to the database file
** are synced prior to the master journal being deleted.
**
** Definition: Two databases (or the same database at two points it time)
** are said to be "logically equivalent" if they give the same answer to
** all queries. Note in particular the content of freelist leaf
** pages can be changed arbitarily without effecting the logical equivalence
** of the database.
**
** (7) At any time, if any subset, including the empty set and the total set,
** of the unsynced changes to a rollback journal are removed and the
** journal is rolled back, the resulting database file will be logical
** equivalent to the database file at the beginning of the transaction.
**
** (8) When a transaction is rolled back, the xTruncate method of the VFS
** is called to restore the database file to the same size it was at
** the beginning of the transaction. (In some VFSes, the xTruncate
** method is a no-op, but that does not change the fact the SQLite will
** invoke it.)
**
** (9) Whenever the database file is modified, at least one bit in the range
** of bytes from 24 through 39 inclusive will be changed prior to releasing
** the EXCLUSIVE lock, thus signaling other connections on the same
** database to flush their caches.
**
** (10) The pattern of bits in bytes 24 through 39 shall not repeat in less
** than one billion transactions.
**
** (11) A database file is well-formed at the beginning and at the conclusion
** of every transaction.
**
** (12) An EXCLUSIVE lock is held on the database file when writing to
** the database file.
**
** (13) A SHARED lock is held on the database file while reading any
** content out of the database file.
**
******************************************************************************/
/*
** Macros for troubleshooting. Normally turned off
*/
#if 0
int sqlite3PagerTrace=1; /* True to enable tracing */
#define sqlite3DebugPrintf printf
#define PAGERTRACE(X) if( sqlite3PagerTrace ){ sqlite3DebugPrintf X; }
#else
#define PAGERTRACE(X)
#endif
/*
** The following two macros are used within the PAGERTRACE() macros above
** to print out file-descriptors.
**
** PAGERID() takes a pointer to a Pager struct as its argument. The
** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
** struct as its argument.
*/
#define PAGERID(p) ((int)(p->fd))
#define FILEHANDLEID(fd) ((int)fd)
/*
** The Pager.eState variable stores the current 'state' of a pager. A
** pager may be in any one of the seven states shown in the following
** state diagram.
**
** OPEN <------+------+
** | | |
** V | |
** +---------> READER-------+ |
** | | |
** | V |
** |<-------WRITER_LOCKED------> ERROR
** | | ^
** | V |
** |<------WRITER_CACHEMOD-------->|
** | | |
** | V |
** |<-------WRITER_DBMOD---------->|
** | | |
** | V |
** +<------WRITER_FINISHED-------->+
**
**
** List of state transitions and the C [function] that performs each:
**
** OPEN -> READER [sqlite3PagerSharedLock]
** READER -> OPEN [pager_unlock]
**
** READER -> WRITER_LOCKED [sqlite3PagerBegin]
** WRITER_LOCKED -> WRITER_CACHEMOD [pager_open_journal]
** WRITER_CACHEMOD -> WRITER_DBMOD [syncJournal]
** WRITER_DBMOD -> WRITER_FINISHED [sqlite3PagerCommitPhaseOne]
** WRITER_*** -> READER [pager_end_transaction]
**
** WRITER_*** -> ERROR [pager_error]
** ERROR -> OPEN [pager_unlock]
**
**
** OPEN:
**
** The pager starts up in this state. Nothing is guaranteed in this
** state - the file may or may not be locked and the database size is
** unknown. The database may not be read or written.
**
** * No read or write transaction is active.
** * Any lock, or no lock at all, may be held on the database file.
** * 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
** open. The database size is known in this state.
**
** A connection running with locking_mode=normal enters this state when
** it opens a read-transaction on the database and returns to state
** OPEN after the read-transaction is completed. However a connection
** running in locking_mode=exclusive (including temp databases) remains in
** this state even after the read-transaction is closed. The only way
** a locking_mode=exclusive connection can transition from READER to OPEN
** is via the ERROR state (see below).
**
** * A read transaction may be active (but a write-transaction cannot).
** * A SHARED or greater lock is held on the database file.
** * The dbSize variable may be trusted (even if a user-level read
** transaction is not active). The dbOrigSize and dbFileSize variables
** may not be trusted at this point.
** * If the database is a WAL database, then the WAL connection is open.
** * Even if a read-transaction is not open, it is guaranteed that
** there is no hot-journal in the file-system.
**
** WRITER_LOCKED:
**
** The pager moves to this state from READER when a write-transaction
** is first opened on the database. In WRITER_LOCKED state, all locks
** required to start a write-transaction are held, but no actual
** modifications to the cache or database have taken place.
**
** In rollback mode, a RESERVED or (if the transaction was opened with
** BEGIN EXCLUSIVE) EXCLUSIVE lock is obtained on the database file when
** moving to this state, but the journal file is not written to or opened
** to in this state. If the transaction is committed or rolled back while
** in WRITER_LOCKED state, all that is required is to unlock the database
** file.
**
** IN WAL mode, WalBeginWriteTransaction() is called to lock the log file.
** If the connection is running with locking_mode=exclusive, an attempt
** is made to obtain an EXCLUSIVE lock on the database file.
**
** * A write transaction is active.
** * If the connection is open in rollback-mode, a RESERVED or greater
** lock is held on the database file.
** * If the connection is open in WAL-mode, a WAL write transaction
** is open (i.e. sqlite3WalBeginWriteTransaction() has been successfully
** called).
** * 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 pager moves from WRITER_LOCKED state to this state when a page is
** first modified by the upper layer. In rollback mode the journal file
** is opened (if it is not already open) and a header written to the
** start of it. The database file on disk has not been modified.
**
** * 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
** to it, but the header has not been synced to disk.
** * The contents of the page cache have been modified.
**
** 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
** and synced to disk.
** * The contents of the page cache have been modified (and possibly
** written to disk).
**
** 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.
** If no error occurred, all that remains is to finalize the journal to
** 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 or disk-full error (including
** SQLITE_IOERR_NOMEM) 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.
**
** Temporary pager files may enter the ERROR state, but in-memory pagers
** cannot.
**
** 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 OPEN 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.
**
** * The Pager.errCode variable is set to something other than SQLITE_OK.
** * There are one or more outstanding references to pages (after the
** last reference is dropped the pager should move back to OPEN state).
** * The pager is not an in-memory pager.
**
**
** Notes:
**
** * A pager is never in WRITER_DBMOD or WRITER_FINISHED state if the
** connection is open in WAL mode. A WAL connection is always in one
** of the first four states.
**
** * Normally, a connection open in exclusive mode is never in PAGER_OPEN
** state. There are two exceptions: immediately after exclusive-mode has
** been turned on (and before any read or write transactions are
** executed), and when the pager is leaving the "error state".
**
** * See also: assert_pager_state().
*/
#define PAGER_OPEN 0
#define PAGER_READER 1
#define PAGER_WRITER_LOCKED 2
#define PAGER_WRITER_CACHEMOD 3
#define PAGER_WRITER_DBMOD 4
#define PAGER_WRITER_FINISHED 5
#define PAGER_ERROR 6
/*
** The Pager.eLock variable is almost always set to one of the
** following locking-states, according to the lock currently held on
** the database file: NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
** This variable is kept up to date as locks are taken and released by
** the pagerLockDb() and pagerUnlockDb() wrappers.
**
** If the VFS xLock() or xUnlock() returns an error other than SQLITE_BUSY
** (i.e. one of the SQLITE_IOERR subtypes), it is not clear whether or not
** the operation was successful. In these circumstances pagerLockDb() and
** pagerUnlockDb() take a conservative approach - eLock is always updated
** when unlocking the file, and only updated when locking the file if the
** VFS call is successful. This way, the Pager.eLock variable may be set
** to a less exclusive (lower) value than the lock that is actually held
** at the system level, but it is never set to a more exclusive value.
**
** This is usually safe. If an xUnlock fails or appears to fail, there may
** be a few redundant xLock() calls or a lock may be held for longer than
** required, but nothing really goes wrong.
**
** The exception is when the database file is unlocked as the pager moves
** from ERROR to OPEN state. At this point there may be a hot-journal file
** in the file-system that needs to be rolled back (as part of a OPEN->SHARED
** transition, by the same pager or any other). If the call to xUnlock()
** fails at this point and the pager is left holding an EXCLUSIVE lock, this
** can confuse the call to xCheckReservedLock() call made later as part
** of hot-journal detection.
**
** xCheckReservedLock() is defined as returning true "if there is a RESERVED
** lock held by this process or any others". So xCheckReservedLock may
** return true because the caller itself is holding an EXCLUSIVE lock (but
** doesn't know it because of a previous error in xUnlock). If this happens
** a hot-journal may be mistaken for a journal being created by an active
** transaction in another process, causing SQLite to read from the database
** without rolling it back.
**
** To work around this, if a call to xUnlock() fails when unlocking the
** database in the ERROR state, Pager.eLock is set to UNKNOWN_LOCK. It
** is only changed back to a real locking state after a successful call
** to xLock(EXCLUSIVE). Also, the code to do the OPEN->SHARED state transition
** omits the check for a hot-journal if Pager.eLock is set to UNKNOWN_LOCK
** lock. Instead, it assumes a hot-journal exists and obtains an EXCLUSIVE
** lock on the database file before attempting to roll it back. See function
** PagerSharedLock() for more detail.
**
** Pager.eLock may only be set to UNKNOWN_LOCK when the pager is in
** PAGER_OPEN state.
*/
#define UNKNOWN_LOCK (EXCLUSIVE_LOCK+1)
/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
# define CODEC2(P,D,N,X,E,O) \
if( P->xCodec==0 ){ O=(char*)D; }else \
if( (O=(char*)(P->xCodec(P->pCodec,D,N,X)))==0 ){ E; }
#else
# define CODEC1(P,D,N,X,E) /* NO-OP */
# define CODEC2(P,D,N,X,E,O) O=(char*)D
#endif
/*
** The maximum allowed sector size. 64KiB. If the xSectorsize() method
** returns a value larger than this, then MAX_SECTOR_SIZE is used instead.
** This could conceivably cause corruption following a power failure on
** such a system. This is currently an undocumented limit.
*/
#define MAX_SECTOR_SIZE 0x10000
/*
** An instance of the following structure is allocated for each active
** savepoint and statement transaction in the system. All such structures
** are stored in the Pager.aSavepoint[] array, which is allocated and
** resized using sqlite3Realloc().
**
** When a savepoint is created, the PagerSavepoint.iHdrOffset field is
** set to 0. If a journal-header is written into the main journal while
** the savepoint is active, then iHdrOffset is set to the byte offset
** immediately following the last journal record written into the main
** journal before the journal-header. This is required during savepoint
** rollback (see pagerPlaybackSavepoint()).
*/
typedef struct PagerSavepoint PagerSavepoint;
struct PagerSavepoint {
i64 iOffset; /* Starting offset in main journal */
i64 iHdrOffset; /* See above */
Bitvec *pInSavepoint; /* Set of pages in this savepoint */
Pgno nOrig; /* Original number of pages in file */
Pgno iSubRec; /* Index of first record in sub-journal */
#ifndef SQLITE_OMIT_WAL
u32 aWalData[WAL_SAVEPOINT_NDATA]; /* WAL savepoint context */
#endif
};
/*
** Bits of the Pager.doNotSpill flag. See further description below.
*/
#define SPILLFLAG_OFF 0x01 /* Never spill cache. Set via pragma */
#define SPILLFLAG_ROLLBACK 0x02 /* Current rolling back, so do not spill */
#define SPILLFLAG_NOSYNC 0x04 /* Spill is ok, but do not sync */
/*
** A open page cache is an instance of struct Pager. A description of
** some of the more important member variables follows:
**
** eState
**
** The current 'state' of the pager object. See the comment and state
** diagram above for a description of the pager state.
**
** eLock
**
** For a real on-disk database, the current lock held on the database file -
** NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
**
** For a temporary or in-memory database (neither of which require any
** locks), this variable is always set to EXCLUSIVE_LOCK. Since such
** databases always have Pager.exclusiveMode==1, this tricks the pager
** logic into thinking that it already has all the locks it will ever
** need (and no reason to release them).
**
** In some (obscure) circumstances, this variable may also be set to
** UNKNOWN_LOCK. See the comment above the #define of UNKNOWN_LOCK for
** details.
**
** changeCountDone
**
** This boolean variable is used to make sure that the change-counter
** (the 4-byte header field at byte offset 24 of the database file) is
** not updated more often than necessary.
**
** It is set to true when the change-counter field is updated, which
** can only happen if an exclusive lock is held on the database file.
** It is cleared (set to false) whenever an exclusive lock is
** relinquished on the database file. Each time a transaction is committed,
** The changeCountDone flag is inspected. If it is true, the work of
** updating the change-counter is omitted for the current transaction.
**
** This mechanism means that when running in exclusive mode, a connection
** need only update the change-counter once, for the first transaction
** committed.
**
** setMaster
**
** 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.
**
** 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
** 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 (and the pager will move to ERROR state).
**
** doNotSpill
**
** This variables control the behavior of cache-spills (calls made by
** the pcache module to the pagerStress() routine to write cached data
** to the file-system in order to free up memory).
**
** When bits SPILLFLAG_OFF or SPILLFLAG_ROLLBACK of doNotSpill are set,
** writing to the database from pagerStress() is disabled altogether.
** The SPILLFLAG_ROLLBACK case is done in a very obscure case that
** comes up during savepoint rollback that requires the pcache module
** to allocate a new page to prevent the journal file from being written
** while it is being traversed by code in pager_playback(). The SPILLFLAG_OFF
** case is a user preference.
**
** If the SPILLFLAG_NOSYNC bit is set, writing to the database from pagerStress()
** is permitted, but syncing the journal file is not. This flag is set
** by sqlite3PagerWrite() when the file-system sector-size is larger than
** the database page-size in order to prevent a journal sync from happening
** in between the journalling of two pages on the same sector.
**
** subjInMemory
**
** This is a boolean variable. If true, then any required sub-journal
** is opened as an in-memory journal file. If false, then in-memory
** sub-journals are only used for in-memory pager files.
**
** This variable is updated by the upper layer each time a new
** write-transaction is opened.
**
** dbSize, dbOrigSize, dbFileSize
**
** Variable dbSize is set to the number of pages in the database file.
** It is valid in PAGER_READER and higher states (all states except for
** OPEN and ERROR).
**
** dbSize is set based on the size of the database file, which may be
** larger than the size of the database (the value stored at offset
** 28 of the database header by the btree). If the size of the file
** is not an integer multiple of the page-size, the value stored in
** dbSize is rounded down (i.e. a 5KB file with 2K page-size has dbSize==2).
** Except, any file that is greater than 0 bytes in size is considered
** to have at least one page. (i.e. a 1KB file with 2K page-size leads
** to dbSize==1).
**
** During a write-transaction, if pages with page-numbers greater than
** dbSize are modified in the cache, dbSize is updated accordingly.
** Similarly, if the database is truncated using PagerTruncateImage(),
** dbSize is updated.
**
** Variables dbOrigSize and dbFileSize are valid in states
** PAGER_WRITER_LOCKED and higher. dbOrigSize is a copy of the dbSize
** variable at the start of the transaction. It is used during rollback,
** and to determine whether or not pages need to be journalled before
** being modified.
**
** Throughout a write-transaction, dbFileSize contains the size of
** the file on disk in pages. It is set to a copy of dbSize when the
** write-transaction is first opened, and updated when VFS calls are made
** to write or truncate the database file on disk.
**
** The only reason the dbFileSize variable is required is to suppress
** unnecessary calls to xTruncate() after committing a transaction. If,
** when a transaction is committed, the dbFileSize variable indicates
** that the database file is larger than the database image (Pager.dbSize),
** pager_truncate() is called. The pager_truncate() call uses xFilesize()
** to measure the database file on disk, and then truncates it if required.
** dbFileSize is not used when rolling back a transaction. In this case
** pager_truncate() is called unconditionally (which means there may be
** a call to xFilesize() that is not strictly required). In either case,
** pager_truncate() may cause the file to become smaller or larger.
**
** dbHintSize
**
** The dbHintSize variable is used to limit the number of calls made to
** the VFS xFileControl(FCNTL_SIZE_HINT) method.
**
** dbHintSize is set to a copy of the dbSize variable when a
** write-transaction is opened (at the same time as dbFileSize and
** dbOrigSize). If the xFileControl(FCNTL_SIZE_HINT) method is called,
** dbHintSize is increased to the number of pages that correspond to the
** size-hint passed to the method call. See pager_write_pagelist() for
** details.
**
** errCode
**
** The Pager.errCode variable is only ever used in PAGER_ERROR state. It
** is set to zero in all other states. In PAGER_ERROR state, Pager.errCode
** is always set to SQLITE_FULL, SQLITE_IOERR or one of the SQLITE_IOERR_XXX
** sub-codes.
*/
struct Pager {
sqlite3_vfs *pVfs; /* OS functions to use for IO */
u8 exclusiveMode; /* Boolean. True if locking_mode==EXCLUSIVE */
u8 journalMode; /* One of the PAGER_JOURNALMODE_* values */
u8 useJournal; /* Use a rollback journal on this file */
u8 noSync; /* Do not sync the journal if true */
u8 fullSync; /* Do extra syncs of the journal for robustness */
u8 ckptSyncFlags; /* SYNC_NORMAL or SYNC_FULL for checkpoint */
u8 walSyncFlags; /* SYNC_NORMAL or SYNC_FULL for wal writes */
u8 syncFlags; /* SYNC_NORMAL or SYNC_FULL otherwise */
u8 tempFile; /* zFilename is a temporary file */
u8 readOnly; /* True for a read-only database */
u8 memDb; /* True to inhibit all file I/O */
/**************************************************************************
** The following block contains those class members that change during
** routine opertion. Class members not in this block are either fixed
** when the pager is first created or else only change when there is a
** significant mode change (such as changing the page_size, locking_mode,
** or the journal_mode). From another view, these class members describe
** the "state" of the pager, while other class members describe the
** "configuration" of the pager.
*/
u8 eState; /* Pager state (OPEN, READER, WRITER_LOCKED..) */
u8 eLock; /* Current lock held on database file */
u8 changeCountDone; /* Set after incrementing the change-counter */
u8 setMaster; /* True if a m-j name has been written to jrnl */
u8 doNotSpill; /* Do not spill the cache when non-zero */
u8 subjInMemory; /* True to use in-memory sub-journals */
Pgno dbSize; /* Number of pages in the database */
Pgno dbOrigSize; /* dbSize before the current transaction */
Pgno dbFileSize; /* Number of pages in the database file */
Pgno dbHintSize; /* Value passed to FCNTL_SIZE_HINT call */
int errCode; /* One of several kinds of errors */
int nRec; /* Pages journalled since last j-header written */
u32 cksumInit; /* Quasi-random value added to every checksum */
u32 nSubRec; /* Number of records written to sub-journal */
Bitvec *pInJournal; /* One bit for each page in the database file */
sqlite3_file *fd; /* File descriptor for database */
sqlite3_file *jfd; /* File descriptor for main journal */
sqlite3_file *sjfd; /* File descriptor for sub-journal */
i64 journalOff; /* Current write offset in the journal file */
i64 journalHdr; /* Byte offset to previous journal header */
sqlite3_backup *pBackup; /* Pointer to list of ongoing backup processes */
PagerSavepoint *aSavepoint; /* Array of active savepoints */
int nSavepoint; /* Number of elements in aSavepoint[] */
char dbFileVers[16]; /* Changes whenever database file changes */
u8 bUseFetch; /* True to use xFetch() */
int nMmapOut; /* Number of mmap pages currently outstanding */
sqlite3_int64 szMmap; /* Desired maximum mmap size */
PgHdr *pMmapFreelist; /* List of free mmap page headers (pDirty) */
/*
** End of the routinely-changing class members
***************************************************************************/
u16 nExtra; /* Add this many bytes to each in-memory page */
i16 nReserve; /* Number of unused bytes at end of each page */
u32 vfsFlags; /* Flags for sqlite3_vfs.xOpen() */
u32 sectorSize; /* Assumed sector size during rollback */
int pageSize; /* Number of bytes in a page */
Pgno mxPgno; /* Maximum allowed size of the database */
i64 journalSizeLimit; /* Size limit for persistent journal files */
char *zFilename; /* Name of the database file */
char *zJournal; /* Name of the journal file */
int (*xBusyHandler)(void*); /* Function to call when busy */
void *pBusyHandlerArg; /* Context argument for xBusyHandler */
int aStat[3]; /* Total cache hits, misses and writes */
#ifdef SQLITE_TEST
int nRead; /* Database pages read */
#endif
void (*xReiniter)(DbPage*); /* Call this routine when reloading pages */
#ifdef SQLITE_HAS_CODEC
void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
void (*xCodecSizeChng)(void*,int,int); /* Notify of page size changes */
void (*xCodecFree)(void*); /* Destructor for the codec */
void *pCodec; /* First argument to xCodec... methods */
#endif
char *pTmpSpace; /* Pager.pageSize bytes of space for tmp use */
PCache *pPCache; /* Pointer to page cache object */
#ifndef SQLITE_OMIT_WAL
Wal *pWal; /* Write-ahead log used by "journal_mode=wal" */
char *zWal; /* File name for write-ahead log */
#endif
};
/*
** Indexes for use with Pager.aStat[]. The Pager.aStat[] array contains
** the values accessed by passing SQLITE_DBSTATUS_CACHE_HIT, CACHE_MISS
** or CACHE_WRITE to sqlite3_db_status().
*/
#define PAGER_STAT_HIT 0
#define PAGER_STAT_MISS 1
#define PAGER_STAT_WRITE 2
/*
** The following global variables hold counters used for
** testing purposes only. These variables do not exist in
** a non-testing build. These variables are not thread-safe.
*/
#ifdef SQLITE_TEST
int sqlite3_pager_readdb_count = 0; /* Number of full pages read from DB */
int sqlite3_pager_writedb_count = 0; /* Number of full pages written to DB */
int sqlite3_pager_writej_count = 0; /* Number of pages written to journal */
# define PAGER_INCR(v) v++
#else
# define PAGER_INCR(v)
#endif
/*
** Journal files begin with the following magic string. The data
** was obtained from /dev/random. It is used only as a sanity check.
**
** Since version 2.8.0, the journal format contains additional sanity
** checking information. If the power fails while the journal is being
** written, semi-random garbage data might appear in the journal
** file after power is restored. If an attempt is then made
** to roll the journal back, the database could be corrupted. The additional
** sanity checking data is an attempt to discover the garbage in the
** journal and ignore it.
**
** The sanity checking information for the new journal format consists
** of a 32-bit checksum on each page of data. The checksum covers both
** the page number and the pPager->pageSize bytes of data for the page.
** This cksum is initialized to a 32-bit random value that appears in the
** journal file right after the header. The random initializer is important,
** because garbage data that appears at the end of a journal is likely
** data that was once in other files that have now been deleted. If the
** garbage data came from an obsolete journal file, the checksums might
** be correct. But by initializing the checksum to random value which
** is different for every journal, we minimize that risk.
*/
static const unsigned char aJournalMagic[] = {
0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
};
/*
** The size of the of each page record in the journal is given by
** the following macro.
*/
#define JOURNAL_PG_SZ(pPager) ((pPager->pageSize) + 8)
/*
** The journal header size for this pager. This is usually the same
** size as a single disk sector. See also setSectorSize().
*/
#define JOURNAL_HDR_SZ(pPager) (pPager->sectorSize)
/*
** The macro MEMDB is true if we are dealing with an in-memory database.
** We do this as a macro so that if the SQLITE_OMIT_MEMORYDB macro is set,
** the value of MEMDB will be a constant and the compiler will optimize
** out code that would never execute.
*/
#ifdef SQLITE_OMIT_MEMORYDB
# define MEMDB 0
#else
# define MEMDB pPager->memDb
#endif
/*
** The macro USEFETCH is true if we are allowed to use the xFetch and xUnfetch
** interfaces to access the database using memory-mapped I/O.
*/
#if SQLITE_MAX_MMAP_SIZE>0
# define USEFETCH(x) ((x)->bUseFetch)
#else
# define USEFETCH(x) 0
#endif
/*
** The maximum legal page number is (2^31 - 1).
*/
#define PAGER_MAX_PGNO 2147483647
/*
** The argument to this macro is a file descriptor (type sqlite3_file*).
** Return 0 if it is not open, or non-zero (but not 1) if it is.
**
** This is so that expressions can be written as:
**
** if( isOpen(pPager->jfd) ){ ...
**
** instead of
**
** if( pPager->jfd->pMethods ){ ...
*/
#define isOpen(pFd) ((pFd)->pMethods)
/*
** Return true if this pager uses a write-ahead log instead of the usual
** rollback journal. Otherwise false.
*/
#ifndef SQLITE_OMIT_WAL
static int pagerUseWal(Pager *pPager){
return (pPager->pWal!=0);
}
#else
# define pagerUseWal(x) 0
# define pagerRollbackWal(x) 0
# define pagerWalFrames(v,w,x,y) 0
# define pagerOpenWalIfPresent(z) SQLITE_OK
# define pagerBeginReadTransaction(z) SQLITE_OK
#endif
#ifndef NDEBUG
/*
** Usage:
**
** assert( assert_pager_state(pPager) );
**
** This function runs many asserts to try to find inconsistencies in
** the internal state of the Pager object.
*/
static int assert_pager_state(Pager *p){
Pager *pPager = p;
/* State must be valid. */
assert( p->eState==PAGER_OPEN
|| p->eState==PAGER_READER
|| p->eState==PAGER_WRITER_LOCKED
|| p->eState==PAGER_WRITER_CACHEMOD
|| p->eState==PAGER_WRITER_DBMOD
|| p->eState==PAGER_WRITER_FINISHED
|| p->eState==PAGER_ERROR
);
/* Regardless of the current state, a temp-file connection always behaves
** as if it has an exclusive lock on the database file. It never updates
** the change-counter field, so the changeCountDone flag is always set.
*/
assert( p->tempFile==0 || p->eLock==EXCLUSIVE_LOCK );
assert( p->tempFile==0 || pPager->changeCountDone );
/* If the useJournal flag is clear, the journal-mode must be "OFF".
** And if the journal-mode is "OFF", the journal file must not be open.
*/
assert( p->journalMode==PAGER_JOURNALMODE_OFF || p->useJournal );
assert( p->journalMode!=PAGER_JOURNALMODE_OFF || !isOpen(p->jfd) );
/* Check that MEMDB implies noSync. And an in-memory journal. Since
** this means an in-memory pager performs no IO at all, it cannot encounter
** either SQLITE_IOERR or SQLITE_FULL during rollback or while finalizing
** a journal file. (although the in-memory journal implementation may
** return SQLITE_IOERR_NOMEM while the journal file is being written). It
** is therefore not possible for an in-memory pager to enter the ERROR
** state.
*/
if( MEMDB ){
assert( p->noSync );
assert( p->journalMode==PAGER_JOURNALMODE_OFF
|| p->journalMode==PAGER_JOURNALMODE_MEMORY
);
assert( p->eState!=PAGER_ERROR && p->eState!=PAGER_OPEN );
assert( pagerUseWal(p)==0 );
}
/* If changeCountDone is set, a RESERVED lock or greater must be held
** on the file.
*/
assert( pPager->changeCountDone==0 || pPager->eLock>=RESERVED_LOCK );
assert( p->eLock!=PENDING_LOCK );
switch( p->eState ){
case PAGER_OPEN:
assert( !MEMDB );
assert( pPager->errCode==SQLITE_OK );
assert( sqlite3PcacheRefCount(pPager->pPCache)==0 || pPager->tempFile );
break;
case PAGER_READER:
assert( pPager->errCode==SQLITE_OK );
assert( p->eLock!=UNKNOWN_LOCK );
assert( p->eLock>=SHARED_LOCK );
break;
case PAGER_WRITER_LOCKED:
assert( p->eLock!=UNKNOWN_LOCK );
assert( pPager->errCode==SQLITE_OK );
if( !pagerUseWal(pPager) ){
assert( p->eLock>=RESERVED_LOCK );
}
assert( pPager->dbSize==pPager->dbOrigSize );
assert( pPager->dbOrigSize==pPager->dbFileSize );
assert( pPager->dbOrigSize==pPager->dbHintSize );
assert( pPager->setMaster==0 );
break;
case PAGER_WRITER_CACHEMOD:
assert( p->eLock!=UNKNOWN_LOCK );
assert( pPager->errCode==SQLITE_OK );
if( !pagerUseWal(pPager) ){
/* It is possible that if journal_mode=wal here that neither the
** journal file nor the WAL file are open. This happens during
** a rollback transaction that switches from journal_mode=off
** to journal_mode=wal.
*/
assert( p->eLock>=RESERVED_LOCK );
assert( isOpen(p->jfd)
|| p->journalMode==PAGER_JOURNALMODE_OFF
|| p->journalMode==PAGER_JOURNALMODE_WAL
);
}
assert( pPager->dbOrigSize==pPager->dbFileSize );
assert( pPager->dbOrigSize==pPager->dbHintSize );
break;
case PAGER_WRITER_DBMOD:
assert( p->eLock==EXCLUSIVE_LOCK );
assert( pPager->errCode==SQLITE_OK );
assert( !pagerUseWal(pPager) );
assert( p->eLock>=EXCLUSIVE_LOCK );
assert( isOpen(p->jfd)
|| p->journalMode==PAGER_JOURNALMODE_OFF
|| p->journalMode==PAGER_JOURNALMODE_WAL
);
assert( pPager->dbOrigSize<=pPager->dbHintSize );
break;
case PAGER_WRITER_FINISHED:
assert( p->eLock==EXCLUSIVE_LOCK );
assert( pPager->errCode==SQLITE_OK );
assert( !pagerUseWal(pPager) );
assert( isOpen(p->jfd)
|| p->journalMode==PAGER_JOURNALMODE_OFF
|| p->journalMode==PAGER_JOURNALMODE_WAL
);
break;
case PAGER_ERROR:
/* There must be at least one outstanding reference to the pager if
** in ERROR state. Otherwise the pager should have already dropped
** back to OPEN state.
*/
assert( pPager->errCode!=SQLITE_OK );
assert( sqlite3PcacheRefCount(pPager->pPCache)>0 );
break;
}
return 1;
}
#endif /* ifndef NDEBUG */
#ifdef SQLITE_DEBUG
/*
** Return a pointer to a human readable string in a static buffer
** containing the state of the Pager object passed as an argument. This
** is intended to be used within debuggers. For example, as an alternative
** to "print *pPager" in gdb:
**
** (gdb) printf "%s", print_pager_state(pPager)
*/
static char *print_pager_state(Pager *p){
static char zRet[1024];
sqlite3_snprintf(1024, zRet,
"Filename: %s\n"
"State: %s errCode=%d\n"
"Lock: %s\n"
"Locking mode: locking_mode=%s\n"
"Journal mode: journal_mode=%s\n"
"Backing store: tempFile=%d memDb=%d useJournal=%d\n"
"Journal: journalOff=%lld journalHdr=%lld\n"
"Size: dbsize=%d dbOrigSize=%d dbFileSize=%d\n"
, p->zFilename
, p->eState==PAGER_OPEN ? "OPEN" :
p->eState==PAGER_READER ? "READER" :
p->eState==PAGER_WRITER_LOCKED ? "WRITER_LOCKED" :
p->eState==PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
p->eState==PAGER_WRITER_DBMOD ? "WRITER_DBMOD" :
p->eState==PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
p->eState==PAGER_ERROR ? "ERROR" : "?error?"
, (int)p->errCode
, p->eLock==NO_LOCK ? "NO_LOCK" :
p->eLock==RESERVED_LOCK ? "RESERVED" :
p->eLock==EXCLUSIVE_LOCK ? "EXCLUSIVE" :
p->eLock==SHARED_LOCK ? "SHARED" :
p->eLock==UNKNOWN_LOCK ? "UNKNOWN" : "?error?"
, p->exclusiveMode ? "exclusive" : "normal"
, p->journalMode==PAGER_JOURNALMODE_MEMORY ? "memory" :