btreeint.h

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*/
struct Btree {
  sqlite3 *db;       /* The database connection holding this btree */
  BtShared *pBt;     /* Sharable content of this btree */
  u8 inTrans;        /* TRANS_NONE, TRANS_READ or TRANS_WRITE */
  u8 sharable;       /* True if we can share pBt with another db */
  u8 locked;         /* True if db currently has pBt locked */
  int wantToLock;    /* Number of nested calls to sqlite3BtreeEnter() */
  Btree *pNext;      /* List of other sharable Btrees from the same db */
  Btree *pPrev;      /* Back pointer of the same list */
};

/*
** Btree.inTrans may take one of the following values.
**
** If the shared-data extension is enabled, there may be multiple users
** of the Btree structure. At most one of these may open a write transaction,
** but any number may have active read transactions.
*/
#define TRANS_NONE  0
#define TRANS_READ  1
#define TRANS_WRITE 2

/*
** An instance of this object represents a single database file.
** 
** A single database file can be in use as the same time by two
** or more database connections.  When two or more connections are
** sharing the same database file, each connection has it own
** private Btree object for the file and each of those Btrees points
** to this one BtShared object.  BtShared.nRef is the number of
** connections currently sharing this database file.
**
** Fields in this structure are accessed under the BtShared.mutex
** mutex, except for nRef and pNext which are accessed under the
** global SQLITE_MUTEX_STATIC_MASTER mutex.  The pPager field
** may not be modified once it is initially set as long as nRef>0.
** The pSchema field may be set once under BtShared.mutex and
** thereafter is unchanged as long as nRef>0.
*/
struct BtShared {
  Pager *pPager;        /* The page cache */
  sqlite3 *db;          /* Database connection currently using this Btree */
  BtCursor *pCursor;    /* A list of all open cursors */
  MemPage *pPage1;      /* First page of the database */
  u8 inStmt;            /* True if we are in a statement subtransaction */
  u8 readOnly;          /* True if the underlying file is readonly */
  u8 maxEmbedFrac;      /* Maximum payload as % of total page size */
  u8 minEmbedFrac;      /* Minimum payload as % of total page size */
  u8 minLeafFrac;       /* Minimum leaf payload as % of total page size */
  u8 pageSizeFixed;     /* True if the page size can no longer be changed */
#ifndef SQLITE_OMIT_AUTOVACUUM
  u8 autoVacuum;        /* True if auto-vacuum is enabled */
  u8 incrVacuum;        /* True if incr-vacuum is enabled */
  Pgno nTrunc;          /* Non-zero if the db will be truncated (incr vacuum) */
#endif
  u16 pageSize;         /* Total number of bytes on a page */
  u16 usableSize;       /* Number of usable bytes on each page */
  int maxLocal;         /* Maximum local payload in non-LEAFDATA tables */
  int minLocal;         /* Minimum local payload in non-LEAFDATA tables */
  int maxLeaf;          /* Maximum local payload in a LEAFDATA table */
  int minLeaf;          /* Minimum local payload in a LEAFDATA table */
  u8 inTransaction;     /* Transaction state */
  int nTransaction;     /* Number of open transactions (read + write) */
  void *pSchema;        /* Pointer to space allocated by sqlite3BtreeSchema() */
  void (*xFreeSchema)(void*);  /* Destructor for BtShared.pSchema */
  sqlite3_mutex *mutex; /* Non-recursive mutex required to access this struct */
  BusyHandler busyHdr;  /* The busy handler for this btree */
#ifndef SQLITE_OMIT_SHARED_CACHE
  int nRef;             /* Number of references to this structure */
  BtShared *pNext;      /* Next on a list of sharable BtShared structs */
  BtLock *pLock;        /* List of locks held on this shared-btree struct */
#endif
};

/*
** An instance of the following structure is used to hold information
** about a cell.  The parseCellPtr() function fills in this structure
** based on information extract from the raw disk page.
*/
typedef struct CellInfo CellInfo;
struct CellInfo {
  u8 *pCell;     /* Pointer to the start of cell content */
  i64 nKey;      /* The key for INTKEY tables, or number of bytes in key */
  u32 nData;     /* Number of bytes of data */
  u32 nPayload;  /* Total amount of payload */
  u16 nHeader;   /* Size of the cell content header in bytes */
  u16 nLocal;    /* Amount of payload held locally */
  u16 iOverflow; /* Offset to overflow page number.  Zero if no overflow */
  u16 nSize;     /* Size of the cell content on the main b-tree page */
};

/*
** A cursor is a pointer to a particular entry within a particular
** b-tree within a database file.
**
** The entry is identified by its MemPage and the index in
** MemPage.aCell[] of the entry.
**
** When a single database file can shared by two more database connections,
** but cursors cannot be shared.  Each cursor is associated with a
** particular database connection identified BtCursor.pBtree.db.
**
** Fields in this structure are accessed under the BtShared.mutex
** found at self->pBt->mutex. 
*/
struct BtCursor {
  Btree *pBtree;            /* The Btree to which this cursor belongs */
  BtShared *pBt;            /* The BtShared this cursor points to */
  BtCursor *pNext, *pPrev;  /* Forms a linked list of all cursors */
  int (*xCompare)(void*,int,const void*,int,const void*); /* Key comp func */
  void *pArg;               /* First arg to xCompare() */
  Pgno pgnoRoot;            /* The root page of this tree */
  MemPage *pPage;           /* Page that contains the entry */
  int idx;                  /* Index of the entry in pPage->aCell[] */
  CellInfo info;            /* A parse of the cell we are pointing at */
  u8 wrFlag;                /* True if writable */
  u8 eState;                /* One of the CURSOR_XXX constants (see below) */
  void *pKey;      /* Saved key that was cursor's last known position */
  i64 nKey;        /* Size of pKey, or last integer key */
  int skip;        /* (skip<0) -> Prev() is a no-op. (skip>0) -> Next() is */
#ifndef SQLITE_OMIT_INCRBLOB
  u8 isIncrblobHandle;      /* True if this cursor is an incr. io handle */
  Pgno *aOverflow;          /* Cache of overflow page locations */
#endif
};

/*
** Potential values for BtCursor.eState.
**
** CURSOR_VALID:
**   Cursor points to a valid entry. getPayload() etc. may be called.
**
** CURSOR_INVALID:
**   Cursor does not point to a valid entry. This can happen (for example) 
**   because the table is empty or because BtreeCursorFirst() has not been
**   called.
**
** CURSOR_REQUIRESEEK:
**   The table that this cursor was opened on still exists, but has been 
**   modified since the cursor was last used. The cursor position is saved
**   in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in 
**   this state, restoreOrClearCursorPosition() can be called to attempt to
**   seek the cursor to the saved position.
**
** CURSOR_FAULT:
**   A unrecoverable error (an I/O error or a malloc failure) has occurred
**   on a different connection that shares the BtShared cache with this
**   cursor.  The error has left the cache in an inconsistent state.
**   Do nothing else with this cursor.  Any attempt to use the cursor
**   should return the error code stored in BtCursor.skip
*/
#define CURSOR_INVALID           0
#define CURSOR_VALID             1
#define CURSOR_REQUIRESEEK       2
#define CURSOR_FAULT             3

/*
** The TRACE macro will print high-level status information about the
** btree operation when the global variable sqlite3_btree_trace is
** enabled.
*/
#if SQLITE_TEST
# define TRACE(X)   if( sqlite3_btree_trace ){ printf X; fflush(stdout); }
#else
# define TRACE(X)
#endif

/*
** Routines to read and write variable-length integers.  These used to
** be defined locally, but now we use the varint routines in the util.c
** file.
*/
#define getVarint    sqlite3GetVarint
#define getVarint32(A,B)  ((*B=*(A))<=0x7f?1:sqlite3GetVarint32(A,B))
#define putVarint    sqlite3PutVarint

/* The database page the PENDING_BYTE occupies. This page is never used.
** TODO: This macro is very similary to PAGER_MJ_PGNO() in pager.c. They
** should possibly be consolidated (presumably in pager.h).
**
** If disk I/O is omitted (meaning that the database is stored purely
** in memory) then there is no pending byte.
*/
#ifdef SQLITE_OMIT_DISKIO
# define PENDING_BYTE_PAGE(pBt)  0x7fffffff
#else
# define PENDING_BYTE_PAGE(pBt) ((PENDING_BYTE/(pBt)->pageSize)+1)
#endif

/*
** A linked list of the following structures is stored at BtShared.pLock.
** Locks are added (or upgraded from READ_LOCK to WRITE_LOCK) when a cursor 
** is opened on the table with root page BtShared.iTable. Locks are removed
** from this list when a transaction is committed or rolled back, or when
** a btree handle is closed.
*/
struct BtLock {
  Btree *pBtree;        /* Btree handle holding this lock */
  Pgno iTable;          /* Root page of table */
  u8 eLock;             /* READ_LOCK or WRITE_LOCK */
  BtLock *pNext;        /* Next in BtShared.pLock list */
};

/* Candidate values for BtLock.eLock */
#define READ_LOCK     1
#define WRITE_LOCK    2

/*
** These macros define the location of the pointer-map entry for a 
** database page. The first argument to each is the number of usable
** bytes on each page of the database (often 1024). The second is the
** page number to look up in the pointer map.
**
** PTRMAP_PAGENO returns the database page number of the pointer-map
** page that stores the required pointer. PTRMAP_PTROFFSET returns
** the offset of the requested map entry.
**
** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page,
** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be
** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements
** this test.
*/
#define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno)
#define PTRMAP_PTROFFSET(pBt, pgno) (5*(pgno-ptrmapPageno(pBt, pgno)-1))
#define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno))

/*
** The pointer map is a lookup table that identifies the parent page for
** each child page in the database file.  The parent page is the page that
** contains a pointer to the child.  Every page in the database contains
** 0 or 1 parent pages.  (In this context 'database page' refers
** to any page that is not part of the pointer map itself.)  Each pointer map
** entry consists of a single byte 'type' and a 4 byte parent page number.
** The PTRMAP_XXX identifiers below are the valid types.
**
** The purpose of the pointer map is to facility moving pages from one
** position in the file to another as part of autovacuum.  When a page
** is moved, the pointer in its parent must be updated to point to the
** new location.  The pointer map is used to locate the parent page quickly.
**
** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not
**                  used in this case.
**
** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number 
**                  is not used in this case.
**
** PTRMAP_OVERFLOW1: The database page is the first page in a list of 
**                   overflow pages. The page number identifies the page that
**                   contains the cell with a pointer to this overflow page.
**
** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of
**                   overflow pages. The page-number identifies the previous
**                   page in the overflow page list.
**
** PTRMAP_BTREE: The database page is a non-root btree page. The page number
**               identifies the parent page in the btree.
*/
#define PTRMAP_ROOTPAGE 1
#define PTRMAP_FREEPAGE 2
#define PTRMAP_OVERFLOW1 3
#define PTRMAP_OVERFLOW2 4
#define PTRMAP_BTREE 5

/* A bunch of assert() statements to check the transaction state variables
** of handle p (type Btree*) are internally consistent.
*/
#define btreeIntegrity(p) \
  assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \
  assert( p->pBt->inTransaction>=p->inTrans ); 


/*
** The ISAUTOVACUUM macro is used within balance_nonroot() to determine
** if the database supports auto-vacuum or not. Because it is used
** within an expression that is an argument to another macro 
** (sqliteMallocRaw), it is not possible to use conditional compilation.
** So, this macro is defined instead.
*/
#ifndef SQLITE_OMIT_AUTOVACUUM
#define ISAUTOVACUUM (pBt->autoVacuum)
#else
#define ISAUTOVACUUM 0
#endif


/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.
*/
typedef struct IntegrityCk IntegrityCk;
struct IntegrityCk {
  BtShared *pBt;    /* The tree being checked out */
  Pager *pPager;    /* The associated pager.  Also accessible by pBt->pPager */
  int nPage;        /* Number of pages in the database */
  int *anRef;       /* Number of times each page is referenced */
  int mxErr;        /* Stop accumulating errors when this reaches zero */
  char *zErrMsg;    /* An error message.  NULL if no errors seen. */
  int nErr;         /* Number of messages written to zErrMsg so far */
};

/*
** Read or write a two- and four-byte big-endian integer values.
*/
#define get2byte(x)   ((x)[0]<<8 | (x)[1])
#define put2byte(p,v) ((p)[0] = (v)>>8, (p)[1] = (v))
#define get4byte sqlite3Get4byte
#define put4byte sqlite3Put4byte

/*
** Internal routines that should be accessed by the btree layer only.
*/
int sqlite3BtreeGetPage(BtShared*, Pgno, MemPage**, int);
int sqlite3BtreeInitPage(MemPage *pPage, MemPage *pParent);
void sqlite3BtreeParseCellPtr(MemPage*, u8*, CellInfo*);
void sqlite3BtreeParseCell(MemPage*, int, CellInfo*);
#ifdef SQLITE_TEST
u8 *sqlite3BtreeFindCell(MemPage *pPage, int iCell);
#endif
int sqlite3BtreeRestoreOrClearCursorPosition(BtCursor *pCur);
void sqlite3BtreeGetTempCursor(BtCursor *pCur, BtCursor *pTempCur);
void sqlite3BtreeReleaseTempCursor(BtCursor *pCur);
int sqlite3BtreeIsRootPage(MemPage *pPage);
void sqlite3BtreeMoveToParent(BtCursor *pCur);