src/memjournal.c

   1 /*
   2 ** 2008 October 7
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 **
  13 ** This file contains code use to implement an in-memory rollback journal.
  14 ** The in-memory rollback journal is used to journal transactions for
  15 ** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
  16 **
  17 ** Update:  The in-memory journal is also used to temporarily cache
  18 ** smaller journals that are not critical for power-loss recovery.
  19 ** For example, statement journals that are not too big will be held
  20 ** entirely in memory, thus reducing the number of file I/O calls, and
  21 ** more importantly, reducing temporary file creation events.  If these
  22 ** journals become too large for memory, they are spilled to disk.  But
  23 ** in the common case, they are usually small and no file I/O needs to
  24 ** occur.
  25 */
  26 #include "sqliteInt.h"
  27
  28 /* Forward references to internal structures */
  29 typedef struct MemJournal MemJournal;
  30 typedef struct FilePoint FilePoint;
  31 typedef struct FileChunk FileChunk;
  32
  33 /*
  34 ** The rollback journal is composed of a linked list of these structures.
  35 **
  36 ** The zChunk array is always at least 8 bytes in size - usually much more.
  37 ** Its actual size is stored in the MemJournal.nChunkSize variable.
  38 */
  39 struct FileChunk {
  40   FileChunk *pNext;               /* Next chunk in the journal */
  41   u8 zChunk[8];                   /* Content of this chunk */
  42 };
  43
  44 /*
  45 ** By default, allocate this many bytes of memory for each FileChunk object.
  46 */
  47 #define MEMJOURNAL_DFLT_FILECHUNKSIZE 1024
  48
  49 /*
  50 ** For chunk size nChunkSize, return the number of bytes that should
  51 ** be allocated for each FileChunk structure.
  52 */
  53 #define fileChunkSize(nChunkSize) (sizeof(FileChunk) + ((nChunkSize)-8))
  54
  55 /*
  56 ** An instance of this object serves as a cursor into the rollback journal.
  57 ** The cursor can be either for reading or writing.
  58 */
  59 struct FilePoint {
  60   sqlite3_int64 iOffset;          /* Offset from the beginning of the file */
  61   FileChunk *pChunk;              /* Specific chunk into which cursor points */
  62 };
  63
  64 /*
  65 ** This structure is a subclass of sqlite3_file. Each open memory-journal
  66 ** is an instance of this class.
  67 */
  68 struct MemJournal {
  69   const sqlite3_io_methods *pMethod; /* Parent class. MUST BE FIRST */
  70   int nChunkSize;                 /* In-memory chunk-size */
  71
  72   int nSpill;                     /* Bytes of data before flushing */
  73   int nSize;                      /* Bytes of data currently in memory */
  74   FileChunk *pFirst;              /* Head of in-memory chunk-list */
  75   FilePoint endpoint;             /* Pointer to the end of the file */
  76   FilePoint readpoint;            /* Pointer to the end of the last xRead() */
  77
  78   int flags;                      /* xOpen flags */
  79   sqlite3_vfs *pVfs;              /* The "real" underlying VFS */
  80   const char *zJournal;           /* Name of the journal file */
  81 };
  82
  83 /*
  84 ** Read data from the in-memory journal file.  This is the implementation
  85 ** of the sqlite3_vfs.xRead method.
  86 */
  87 static int memjrnlRead(
  88   sqlite3_file *pJfd,    /* The journal file from which to read */
  89   void *zBuf,            /* Put the results here */
  90   int iAmt,              /* Number of bytes to read */
  91   sqlite_int64 iOfst     /* Begin reading at this offset */
  92 ){
  93   MemJournal *p = (MemJournal *)pJfd;
  94   u8 *zOut = zBuf;
  95   int nRead = iAmt;
  96   int iChunkOffset;
  97   FileChunk *pChunk;
  98
  99 #ifdef SQLITE_ENABLE_ATOMIC_WRITE
 100   if( (iAmt+iOfst)>p->endpoint.iOffset ){
 101     return SQLITE_IOERR_SHORT_READ;
 102   }
 103 #endif
 104
 105   assert( (iAmt+iOfst)<=p->endpoint.iOffset );
 106   assert( p->readpoint.iOffset==0 || p->readpoint.pChunk!=0 );
 107   if( p->readpoint.iOffset!=iOfst || iOfst==0 ){
 108     sqlite3_int64 iOff = 0;
 109     for(pChunk=p->pFirst;
 110         ALWAYS(pChunk) && (iOff+p->nChunkSize)<=iOfst;
 111         pChunk=pChunk->pNext
 112     ){
 113       iOff += p->nChunkSize;
 114     }
 115   }else{
 116     pChunk = p->readpoint.pChunk;
 117     assert( pChunk!=0 );
 118   }
 119
 120   iChunkOffset = (int)(iOfst%p->nChunkSize);
 121   do {
 122     int iSpace = p->nChunkSize - iChunkOffset;
 123     int nCopy = MIN(nRead, (p->nChunkSize - iChunkOffset));
 124     memcpy(zOut, (u8*)pChunk->zChunk + iChunkOffset, nCopy);
 125     zOut += nCopy;
 126     nRead -= iSpace;
 127     iChunkOffset = 0;
 128   } while( nRead>=0 && (pChunk=pChunk->pNext)!=0 && nRead>0 );
 129   p->readpoint.iOffset = pChunk ? iOfst+iAmt : 0;
 130   p->readpoint.pChunk = pChunk;
 131
 132   return SQLITE_OK;
 133 }
 134
 135 /*
 136 ** Free the list of FileChunk structures headed at MemJournal.pFirst.
 137 */
 138 static void memjrnlFreeChunks(MemJournal *p){
 139   FileChunk *pIter;
 140   FileChunk *pNext;
 141   for(pIter=p->pFirst; pIter; pIter=pNext){
 142     pNext = pIter->pNext;
 143     sqlite3_free(pIter);
 144   }
 145   p->pFirst = 0;
 146 }
 147
 148 /*
 149 ** Flush the contents of memory to a real file on disk.
 150 */
 151 static int memjrnlCreateFile(MemJournal *p){
 152   int rc;
 153   sqlite3_file *pReal = (sqlite3_file*)p;
 154   MemJournal copy = *p;
 155
 156   memset(p, 0, sizeof(MemJournal));
 157   rc = sqlite3OsOpen(copy.pVfs, copy.zJournal, pReal, copy.flags, 0);
 158   if( rc==SQLITE_OK ){
 159     int nChunk = copy.nChunkSize;
 160     i64 iOff = 0;
 161     FileChunk *pIter;
 162     for(pIter=copy.pFirst; pIter; pIter=pIter->pNext){
 163       if( iOff + nChunk > copy.endpoint.iOffset ){
 164         nChunk = copy.endpoint.iOffset - iOff;
 165       }
 166       rc = sqlite3OsWrite(pReal, (u8*)pIter->zChunk, nChunk, iOff);
 167       if( rc ) break;
 168       iOff += nChunk;
 169     }
 170     if( rc==SQLITE_OK ){
 171       /* No error has occurred. Free the in-memory buffers. */
 172       memjrnlFreeChunks(&copy);
 173     }
 174   }
 175   if( rc!=SQLITE_OK ){
 176     /* If an error occurred while creating or writing to the file, restore
 177     ** the original before returning. This way, SQLite uses the in-memory
 178     ** journal data to roll back changes made to the internal page-cache
 179     ** before this function was called.  */
 180     sqlite3OsClose(pReal);
 181     *p = copy;
 182   }
 183   return rc;
 184 }
 185
 186
 187 /*
 188 ** Write data to the file.
 189 */
 190 static int memjrnlWrite(
 191   sqlite3_file *pJfd,    /* The journal file into which to write */
 192   const void *zBuf,      /* Take data to be written from here */
 193   int iAmt,              /* Number of bytes to write */
 194   sqlite_int64 iOfst     /* Begin writing at this offset into the file */
 195 ){
 196   MemJournal *p = (MemJournal *)pJfd;
 197   int nWrite = iAmt;
 198   u8 *zWrite = (u8 *)zBuf;
 199
 200   /* If the file should be created now, create it and write the new data
 201   ** into the file on disk. */
 202   if( p->nSpill>0 && (iAmt+iOfst)>p->nSpill ){
 203     int rc = memjrnlCreateFile(p);
 204     if( rc==SQLITE_OK ){
 205       rc = sqlite3OsWrite(pJfd, zBuf, iAmt, iOfst);
 206     }
 207     return rc;
 208   }
 209
 210   /* If the contents of this write should be stored in memory */
 211   else{
 212     /* An in-memory journal file should only ever be appended to. Random
 213     ** access writes are not required. The only exception to this is when
 214     ** the in-memory journal is being used by a connection using the
 215     ** atomic-write optimization. In this case the first 28 bytes of the
 216     ** journal file may be written as part of committing the transaction. */
 217     assert( iOfst==p->endpoint.iOffset || iOfst==0 );
 218 #ifdef SQLITE_ENABLE_ATOMIC_WRITE
 219     if( iOfst==0 && p->pFirst ){
 220       assert( p->nChunkSize>iAmt );
 221       memcpy((u8*)p->pFirst->zChunk, zBuf, iAmt);
 222     }else
 223 #else
 224     assert( iOfst>0 || p->pFirst==0 );
 225 #endif
 226     {
 227       while( nWrite>0 ){
 228         FileChunk *pChunk = p->endpoint.pChunk;
 229         int iChunkOffset = (int)(p->endpoint.iOffset%p->nChunkSize);
 230         int iSpace = MIN(nWrite, p->nChunkSize - iChunkOffset);
 231
 232         if( iChunkOffset==0 ){
 233           /* New chunk is required to extend the file. */
 234           FileChunk *pNew = sqlite3_malloc(fileChunkSize(p->nChunkSize));
 235           if( !pNew ){
 236             return SQLITE_IOERR_NOMEM_BKPT;
 237           }
 238           pNew->pNext = 0;
 239           if( pChunk ){
 240             assert( p->pFirst );
 241             pChunk->pNext = pNew;
 242           }else{
 243             assert( !p->pFirst );
 244             p->pFirst = pNew;
 245           }
 246           p->endpoint.pChunk = pNew;
 247         }
 248
 249         memcpy((u8*)p->endpoint.pChunk->zChunk + iChunkOffset, zWrite, iSpace);
 250         zWrite += iSpace;
 251         nWrite -= iSpace;
 252         p->endpoint.iOffset += iSpace;
 253       }
 254       p->nSize = iAmt + iOfst;
 255     }
 256   }
 257
 258   return SQLITE_OK;
 259 }
 260
 261 /*
 262 ** Truncate the file.
 263 **
 264 ** If the journal file is already on disk, truncate it there. Or, if it
 265 ** is still in main memory but is being truncated to zero bytes in size,
 266 ** ignore
 267 */
 268 static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
 269   MemJournal *p = (MemJournal *)pJfd;
 270   if( ALWAYS(size==0) ){
 271     memjrnlFreeChunks(p);
 272     p->nSize = 0;
 273     p->endpoint.pChunk = 0;
 274     p->endpoint.iOffset = 0;
 275     p->readpoint.pChunk = 0;
 276     p->readpoint.iOffset = 0;
 277   }
 278   return SQLITE_OK;
 279 }
 280
 281 /*
 282 ** Close the file.
 283 */
 284 static int memjrnlClose(sqlite3_file *pJfd){
 285   MemJournal *p = (MemJournal *)pJfd;
 286   memjrnlFreeChunks(p);
 287   return SQLITE_OK;
 288 }
 289
 290 /*
 291 ** Sync the file.
 292 **
 293 ** If the real file has been created, call its xSync method. Otherwise,
 294 ** syncing an in-memory journal is a no-op.
 295 */
 296 static int memjrnlSync(sqlite3_file *pJfd, int flags){
 297   UNUSED_PARAMETER2(pJfd, flags);
 298   return SQLITE_OK;
 299 }
 300
 301 /*
 302 ** Query the size of the file in bytes.
 303 */
 304 static int memjrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
 305   MemJournal *p = (MemJournal *)pJfd;
 306   *pSize = (sqlite_int64) p->endpoint.iOffset;
 307   return SQLITE_OK;
 308 }
 309
 310 /*
 311 ** Table of methods for MemJournal sqlite3_file object.
 312 */
 313 static const struct sqlite3_io_methods MemJournalMethods = {
 314   1,                /* iVersion */
 315   memjrnlClose,     /* xClose */
 316   memjrnlRead,      /* xRead */
 317   memjrnlWrite,     /* xWrite */
 318   memjrnlTruncate,  /* xTruncate */
 319   memjrnlSync,      /* xSync */
 320   memjrnlFileSize,  /* xFileSize */
 321   0,                /* xLock */
 322   0,                /* xUnlock */
 323   0,                /* xCheckReservedLock */
 324   0,                /* xFileControl */
 325   0,                /* xSectorSize */
 326   0,                /* xDeviceCharacteristics */
 327   0,                /* xShmMap */
 328   0,                /* xShmLock */
 329   0,                /* xShmBarrier */
 330   0,                /* xShmUnmap */
 331   0,                /* xFetch */
 332   0                 /* xUnfetch */
 333 };
 334
 335 /*
 336 ** Open a journal file.
 337 **
 338 ** The behaviour of the journal file depends on the value of parameter
 339 ** nSpill. If nSpill is 0, then the journal file is always create and
 340 ** accessed using the underlying VFS. If nSpill is less than zero, then
 341 ** all content is always stored in main-memory. Finally, if nSpill is a
 342 ** positive value, then the journal file is initially created in-memory
 343 ** but may be flushed to disk later on. In this case the journal file is
 344 ** flushed to disk either when it grows larger than nSpill bytes in size,
 345 ** or when sqlite3JournalCreate() is called.
 346 */
 347 int sqlite3JournalOpen(
 348   sqlite3_vfs *pVfs,         /* The VFS to use for actual file I/O */
 349   const char *zName,         /* Name of the journal file */
 350   sqlite3_file *pJfd,        /* Preallocated, blank file handle */
 351   int flags,                 /* Opening flags */
 352   int nSpill                 /* Bytes buffered before opening the file */
 353 ){
 354   MemJournal *p = (MemJournal*)pJfd;
 355
 356   /* Zero the file-handle object. If nSpill was passed zero, initialize
 357   ** it using the sqlite3OsOpen() function of the underlying VFS. In this
 358   ** case none of the code in this module is executed as a result of calls
 359   ** made on the journal file-handle.  */
 360   memset(p, 0, sizeof(MemJournal));
 361   if( nSpill==0 ){
 362     return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
 363   }
 364
 365   if( nSpill>0 ){
 366     p->nChunkSize = nSpill;
 367   }else{
 368     p->nChunkSize = 8 + MEMJOURNAL_DFLT_FILECHUNKSIZE - sizeof(FileChunk);
 369     assert( MEMJOURNAL_DFLT_FILECHUNKSIZE==fileChunkSize(p->nChunkSize) );
 370   }
 371
 372   p->pMethod = (const sqlite3_io_methods*)&MemJournalMethods;
 373   p->nSpill = nSpill;
 374   p->flags = flags;
 375   p->zJournal = zName;
 376   p->pVfs = pVfs;
 377   return SQLITE_OK;
 378 }
 379
 380 /*
 381 ** Open an in-memory journal file.
 382 */
 383 void sqlite3MemJournalOpen(sqlite3_file *pJfd){
 384   sqlite3JournalOpen(0, 0, pJfd, 0, -1);
 385 }
 386
 387 #ifdef SQLITE_ENABLE_ATOMIC_WRITE
 388 /*
 389 ** If the argument p points to a MemJournal structure that is not an
 390 ** in-memory-only journal file (i.e. is one that was opened with a +ve
 391 ** nSpill parameter), and the underlying file has not yet been created,
 392 ** create it now.
 393 */
 394 int sqlite3JournalCreate(sqlite3_file *p){
 395   int rc = SQLITE_OK;
 396   if( p->pMethods==&MemJournalMethods && ((MemJournal*)p)->nSpill>0 ){
 397     rc = memjrnlCreateFile((MemJournal*)p);
 398   }
 399   return rc;
 400 }
 401 #endif
 402
 403 /*
 404 ** The file-handle passed as the only argument is open on a journal file.
 405 ** Return true if this "journal file" is currently stored in heap memory,
 406 ** or false otherwise.
 407 */
 408 int sqlite3JournalIsInMemory(sqlite3_file *p){
 409   return p->pMethods==&MemJournalMethods;
 410 }
 411
 412 /*
 413 ** Return the number of bytes required to store a JournalFile that uses vfs
 414 ** pVfs to create the underlying on-disk files.
 415 */
 416 int sqlite3JournalSize(sqlite3_vfs *pVfs){
 417   return MAX(pVfs->szOsFile, (int)sizeof(MemJournal));
 418 }