src/dbstat.c

   1 /*
   2 ** 2010 July 12
   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 an implementation of the "dbstat" virtual table.
  14 **
  15 ** The dbstat virtual table is used to extract low-level formatting
  16 ** information from an SQLite database in order to implement the
  17 ** "sqlite3_analyzer" utility.  See the ../tool/spaceanal.tcl script
  18 ** for an example implementation.
  19 **
  20 ** Additional information is available on the "dbstat.html" page of the
  21 ** official SQLite documentation.
  22 */
  23
  24 #include "sqliteInt.h"   /* Requires access to internal data structures */
  25 #if (defined(SQLITE_ENABLE_DBSTAT_VTAB) || defined(SQLITE_TEST)) \
  26     && !defined(SQLITE_OMIT_VIRTUALTABLE)
  27
  28 /*
  29 ** Page paths:
  30 **
  31 **   The value of the 'path' column describes the path taken from the
  32 **   root-node of the b-tree structure to each page. The value of the
  33 **   root-node path is '/'.
  34 **
  35 **   The value of the path for the left-most child page of the root of
  36 **   a b-tree is '/000/'. (Btrees store content ordered from left to right
  37 **   so the pages to the left have smaller keys than the pages to the right.)
  38 **   The next to left-most child of the root page is
  39 **   '/001', and so on, each sibling page identified by a 3-digit hex
  40 **   value. The children of the 451st left-most sibling have paths such
  41 **   as '/1c2/000/, '/1c2/001/' etc.
  42 **
  43 **   Overflow pages are specified by appending a '+' character and a
  44 **   six-digit hexadecimal value to the path to the cell they are linked
  45 **   from. For example, the three overflow pages in a chain linked from
  46 **   the left-most cell of the 450th child of the root page are identified
  47 **   by the paths:
  48 **
  49 **      '/1c2/000+000000'         // First page in overflow chain
  50 **      '/1c2/000+000001'         // Second page in overflow chain
  51 **      '/1c2/000+000002'         // Third page in overflow chain
  52 **
  53 **   If the paths are sorted using the BINARY collation sequence, then
  54 **   the overflow pages associated with a cell will appear earlier in the
  55 **   sort-order than its child page:
  56 **
  57 **      '/1c2/000/'               // Left-most child of 451st child of root
  58 */
  59 #define VTAB_SCHEMA                                                         \
  60   "CREATE TABLE xx( "                                                       \
  61   "  name       TEXT,             /* Name of table or index */"             \
  62   "  path       TEXT,             /* Path to page from root */"             \
  63   "  pageno     INTEGER,          /* Page number */"                        \
  64   "  pagetype   TEXT,             /* 'internal', 'leaf' or 'overflow' */"   \
  65   "  ncell      INTEGER,          /* Cells on page (0 for overflow) */"     \
  66   "  payload    INTEGER,          /* Bytes of payload on this page */"      \
  67   "  unused     INTEGER,          /* Bytes of unused space on this page */" \
  68   "  mx_payload INTEGER,          /* Largest payload size of all cells */"  \
  69   "  pgoffset   INTEGER,          /* Offset of page in file */"             \
  70   "  pgsize     INTEGER,          /* Size of the page */"                   \
  71   "  schema     TEXT HIDDEN       /* Database schema being analyzed */"     \
  72   ");"
  73
  74
  75 typedef struct StatTable StatTable;
  76 typedef struct StatCursor StatCursor;
  77 typedef struct StatPage StatPage;
  78 typedef struct StatCell StatCell;
  79
  80 struct StatCell {
  81   int nLocal;                     /* Bytes of local payload */
  82   u32 iChildPg;                   /* Child node (or 0 if this is a leaf) */
  83   int nOvfl;                      /* Entries in aOvfl[] */
  84   u32 *aOvfl;                     /* Array of overflow page numbers */
  85   int nLastOvfl;                  /* Bytes of payload on final overflow page */
  86   int iOvfl;                      /* Iterates through aOvfl[] */
  87 };
  88
  89 struct StatPage {
  90   u32 iPgno;
  91   DbPage *pPg;
  92   int iCell;
  93
  94   char *zPath;                    /* Path to this page */
  95
  96   /* Variables populated by statDecodePage(): */
  97   u8 flags;                       /* Copy of flags byte */
  98   int nCell;                      /* Number of cells on page */
  99   int nUnused;                    /* Number of unused bytes on page */
 100   StatCell *aCell;                /* Array of parsed cells */
 101   u32 iRightChildPg;              /* Right-child page number (or 0) */
 102   int nMxPayload;                 /* Largest payload of any cell on this page */
 103 };
 104
 105 struct StatCursor {
 106   sqlite3_vtab_cursor base;
 107   sqlite3_stmt *pStmt;            /* Iterates through set of root pages */
 108   int isEof;                      /* After pStmt has returned SQLITE_DONE */
 109   int iDb;                        /* Schema used for this query */
 110
 111   StatPage aPage[32];
 112   int iPage;                      /* Current entry in aPage[] */
 113
 114   /* Values to return. */
 115   char *zName;                    /* Value of 'name' column */
 116   char *zPath;                    /* Value of 'path' column */
 117   u32 iPageno;                    /* Value of 'pageno' column */
 118   char *zPagetype;                /* Value of 'pagetype' column */
 119   int nCell;                      /* Value of 'ncell' column */
 120   int nPayload;                   /* Value of 'payload' column */
 121   int nUnused;                    /* Value of 'unused' column */
 122   int nMxPayload;                 /* Value of 'mx_payload' column */
 123   i64 iOffset;                    /* Value of 'pgOffset' column */
 124   int szPage;                     /* Value of 'pgSize' column */
 125 };
 126
 127 struct StatTable {
 128   sqlite3_vtab base;
 129   sqlite3 *db;
 130   int iDb;                        /* Index of database to analyze */
 131 };
 132
 133 #ifndef get2byte
 134 # define get2byte(x)   ((x)[0]<<8 | (x)[1])
 135 #endif
 136
 137 /*
 138 ** Connect to or create a statvfs virtual table.
 139 */
 140 static int statConnect(
 141   sqlite3 *db,
 142   void *pAux,
 143   int argc, const char *const*argv,
 144   sqlite3_vtab **ppVtab,
 145   char **pzErr
 146 ){
 147   StatTable *pTab = 0;
 148   int rc = SQLITE_OK;
 149   int iDb;
 150
 151   if( argc>=4 ){
 152     Token nm;
 153     sqlite3TokenInit(&nm, (char*)argv[3]);
 154     iDb = sqlite3FindDb(db, &nm);
 155     if( iDb<0 ){
 156       *pzErr = sqlite3_mprintf("no such database: %s", argv[3]);
 157       return SQLITE_ERROR;
 158     }
 159   }else{
 160     iDb = 0;
 161   }
 162   rc = sqlite3_declare_vtab(db, VTAB_SCHEMA);
 163   if( rc==SQLITE_OK ){
 164     pTab = (StatTable *)sqlite3_malloc64(sizeof(StatTable));
 165     if( pTab==0 ) rc = SQLITE_NOMEM_BKPT;
 166   }
 167
 168   assert( rc==SQLITE_OK || pTab==0 );
 169   if( rc==SQLITE_OK ){
 170     memset(pTab, 0, sizeof(StatTable));
 171     pTab->db = db;
 172     pTab->iDb = iDb;
 173   }
 174
 175   *ppVtab = (sqlite3_vtab*)pTab;
 176   return rc;
 177 }
 178
 179 /*
 180 ** Disconnect from or destroy a statvfs virtual table.
 181 */
 182 static int statDisconnect(sqlite3_vtab *pVtab){
 183   sqlite3_free(pVtab);
 184   return SQLITE_OK;
 185 }
 186
 187 /*
 188 ** There is no "best-index". This virtual table always does a linear
 189 ** scan.  However, a schema=? constraint should cause this table to
 190 ** operate on a different database schema, so check for it.
 191 **
 192 ** idxNum is normally 0, but will be 1 if a schema=? constraint exists.
 193 */
 194 static int statBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
 195   int i;
 196
 197   pIdxInfo->estimatedCost = 1.0e6;  /* Initial cost estimate */
 198
 199   /* Look for a valid schema=? constraint.  If found, change the idxNum to
 200   ** 1 and request the value of that constraint be sent to xFilter.  And
 201   ** lower the cost estimate to encourage the constrained version to be
 202   ** used.
 203   */
 204   for(i=0; i<pIdxInfo->nConstraint; i++){
 205     if( pIdxInfo->aConstraint[i].usable==0 ) continue;
 206     if( pIdxInfo->aConstraint[i].op!=SQLITE_INDEX_CONSTRAINT_EQ ) continue;
 207     if( pIdxInfo->aConstraint[i].iColumn!=10 ) continue;
 208     pIdxInfo->idxNum = 1;
 209     pIdxInfo->estimatedCost = 1.0;
 210     pIdxInfo->aConstraintUsage[i].argvIndex = 1;
 211     pIdxInfo->aConstraintUsage[i].omit = 1;
 212     break;
 213   }
 214
 215
 216   /* Records are always returned in ascending order of (name, path).
 217   ** If this will satisfy the client, set the orderByConsumed flag so that
 218   ** SQLite does not do an external sort.
 219   */
 220   if( ( pIdxInfo->nOrderBy==1
 221      && pIdxInfo->aOrderBy[0].iColumn==0
 222      && pIdxInfo->aOrderBy[0].desc==0
 223      ) ||
 224       ( pIdxInfo->nOrderBy==2
 225      && pIdxInfo->aOrderBy[0].iColumn==0
 226      && pIdxInfo->aOrderBy[0].desc==0
 227      && pIdxInfo->aOrderBy[1].iColumn==1
 228      && pIdxInfo->aOrderBy[1].desc==0
 229      )
 230   ){
 231     pIdxInfo->orderByConsumed = 1;
 232   }
 233
 234   return SQLITE_OK;
 235 }
 236
 237 /*
 238 ** Open a new statvfs cursor.
 239 */
 240 static int statOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
 241   StatTable *pTab = (StatTable *)pVTab;
 242   StatCursor *pCsr;
 243
 244   pCsr = (StatCursor *)sqlite3_malloc64(sizeof(StatCursor));
 245   if( pCsr==0 ){
 246     return SQLITE_NOMEM_BKPT;
 247   }else{
 248     memset(pCsr, 0, sizeof(StatCursor));
 249     pCsr->base.pVtab = pVTab;
 250     pCsr->iDb = pTab->iDb;
 251   }
 252
 253   *ppCursor = (sqlite3_vtab_cursor *)pCsr;
 254   return SQLITE_OK;
 255 }
 256
 257 static void statClearPage(StatPage *p){
 258   int i;
 259   if( p->aCell ){
 260     for(i=0; i<p->nCell; i++){
 261       sqlite3_free(p->aCell[i].aOvfl);
 262     }
 263     sqlite3_free(p->aCell);
 264   }
 265   sqlite3PagerUnref(p->pPg);
 266   sqlite3_free(p->zPath);
 267   memset(p, 0, sizeof(StatPage));
 268 }
 269
 270 static void statResetCsr(StatCursor *pCsr){
 271   int i;
 272   sqlite3_reset(pCsr->pStmt);
 273   for(i=0; i<ArraySize(pCsr->aPage); i++){
 274     statClearPage(&pCsr->aPage[i]);
 275   }
 276   pCsr->iPage = 0;
 277   sqlite3_free(pCsr->zPath);
 278   pCsr->zPath = 0;
 279   pCsr->isEof = 0;
 280 }
 281
 282 /*
 283 ** Close a statvfs cursor.
 284 */
 285 static int statClose(sqlite3_vtab_cursor *pCursor){
 286   StatCursor *pCsr = (StatCursor *)pCursor;
 287   statResetCsr(pCsr);
 288   sqlite3_finalize(pCsr->pStmt);
 289   sqlite3_free(pCsr);
 290   return SQLITE_OK;
 291 }
 292
 293 static void getLocalPayload(
 294   int nUsable,                    /* Usable bytes per page */
 295   u8 flags,                       /* Page flags */
 296   int nTotal,                     /* Total record (payload) size */
 297   int *pnLocal                    /* OUT: Bytes stored locally */
 298 ){
 299   int nLocal;
 300   int nMinLocal;
 301   int nMaxLocal;
 302
 303   if( flags==0x0D ){              /* Table leaf node */
 304     nMinLocal = (nUsable - 12) * 32 / 255 - 23;
 305     nMaxLocal = nUsable - 35;
 306   }else{                          /* Index interior and leaf nodes */
 307     nMinLocal = (nUsable - 12) * 32 / 255 - 23;
 308     nMaxLocal = (nUsable - 12) * 64 / 255 - 23;
 309   }
 310
 311   nLocal = nMinLocal + (nTotal - nMinLocal) % (nUsable - 4);
 312   if( nLocal>nMaxLocal ) nLocal = nMinLocal;
 313   *pnLocal = nLocal;
 314 }
 315
 316 static int statDecodePage(Btree *pBt, StatPage *p){
 317   int nUnused;
 318   int iOff;
 319   int nHdr;
 320   int isLeaf;
 321   int szPage;
 322
 323   u8 *aData = sqlite3PagerGetData(p->pPg);
 324   u8 *aHdr = &aData[p->iPgno==1 ? 100 : 0];
 325
 326   p->flags = aHdr[0];
 327   p->nCell = get2byte(&aHdr[3]);
 328   p->nMxPayload = 0;
 329
 330   isLeaf = (p->flags==0x0A || p->flags==0x0D);
 331   nHdr = 12 - isLeaf*4 + (p->iPgno==1)*100;
 332
 333   nUnused = get2byte(&aHdr[5]) - nHdr - 2*p->nCell;
 334   nUnused += (int)aHdr[7];
 335   iOff = get2byte(&aHdr[1]);
 336   while( iOff ){
 337     nUnused += get2byte(&aData[iOff+2]);
 338     iOff = get2byte(&aData[iOff]);
 339   }
 340   p->nUnused = nUnused;
 341   p->iRightChildPg = isLeaf ? 0 : sqlite3Get4byte(&aHdr[8]);
 342   szPage = sqlite3BtreeGetPageSize(pBt);
 343
 344   if( p->nCell ){
 345     int i;                        /* Used to iterate through cells */
 346     int nUsable;                  /* Usable bytes per page */
 347
 348     sqlite3BtreeEnter(pBt);
 349     nUsable = szPage - sqlite3BtreeGetReserveNoMutex(pBt);
 350     sqlite3BtreeLeave(pBt);
 351     p->aCell = sqlite3_malloc64((p->nCell+1) * sizeof(StatCell));
 352     if( p->aCell==0 ) return SQLITE_NOMEM_BKPT;
 353     memset(p->aCell, 0, (p->nCell+1) * sizeof(StatCell));
 354
 355     for(i=0; i<p->nCell; i++){
 356       StatCell *pCell = &p->aCell[i];
 357
 358       iOff = get2byte(&aData[nHdr+i*2]);
 359       if( !isLeaf ){
 360         pCell->iChildPg = sqlite3Get4byte(&aData[iOff]);
 361         iOff += 4;
 362       }
 363       if( p->flags==0x05 ){
 364         /* A table interior node. nPayload==0. */
 365       }else{
 366         u32 nPayload;             /* Bytes of payload total (local+overflow) */
 367         int nLocal;               /* Bytes of payload stored locally */
 368         iOff += getVarint32(&aData[iOff], nPayload);
 369         if( p->flags==0x0D ){
 370           u64 dummy;
 371           iOff += sqlite3GetVarint(&aData[iOff], &dummy);
 372         }
 373         if( nPayload>(u32)p->nMxPayload ) p->nMxPayload = nPayload;
 374         getLocalPayload(nUsable, p->flags, nPayload, &nLocal);
 375         pCell->nLocal = nLocal;
 376         assert( nLocal>=0 );
 377         assert( nPayload>=(u32)nLocal );
 378         assert( nLocal<=(nUsable-35) );
 379         if( nPayload>(u32)nLocal ){
 380           int j;
 381           int nOvfl = ((nPayload - nLocal) + nUsable-4 - 1) / (nUsable - 4);
 382           pCell->nLastOvfl = (nPayload-nLocal) - (nOvfl-1) * (nUsable-4);
 383           pCell->nOvfl = nOvfl;
 384           pCell->aOvfl = sqlite3_malloc64(sizeof(u32)*nOvfl);
 385           if( pCell->aOvfl==0 ) return SQLITE_NOMEM_BKPT;
 386           pCell->aOvfl[0] = sqlite3Get4byte(&aData[iOff+nLocal]);
 387           for(j=1; j<nOvfl; j++){
 388             int rc;
 389             u32 iPrev = pCell->aOvfl[j-1];
 390             DbPage *pPg = 0;
 391             rc = sqlite3PagerGet(sqlite3BtreePager(pBt), iPrev, &pPg, 0);
 392             if( rc!=SQLITE_OK ){
 393               assert( pPg==0 );
 394               return rc;
 395             }
 396             pCell->aOvfl[j] = sqlite3Get4byte(sqlite3PagerGetData(pPg));
 397             sqlite3PagerUnref(pPg);
 398           }
 399         }
 400       }
 401     }
 402   }
 403
 404   return SQLITE_OK;
 405 }
 406
 407 /*
 408 ** Populate the pCsr->iOffset and pCsr->szPage member variables. Based on
 409 ** the current value of pCsr->iPageno.
 410 */
 411 static void statSizeAndOffset(StatCursor *pCsr){
 412   StatTable *pTab = (StatTable *)((sqlite3_vtab_cursor *)pCsr)->pVtab;
 413   Btree *pBt = pTab->db->aDb[pTab->iDb].pBt;
 414   Pager *pPager = sqlite3BtreePager(pBt);
 415   sqlite3_file *fd;
 416   sqlite3_int64 x[2];
 417
 418   /* The default page size and offset */
 419   pCsr->szPage = sqlite3BtreeGetPageSize(pBt);
 420   pCsr->iOffset = (i64)pCsr->szPage * (pCsr->iPageno - 1);
 421
 422   /* If connected to a ZIPVFS backend, override the page size and
 423   ** offset with actual values obtained from ZIPVFS.
 424   */
 425   fd = sqlite3PagerFile(pPager);
 426   x[0] = pCsr->iPageno;
 427   if( fd->pMethods!=0 && sqlite3OsFileControl(fd, 230440, &x)==SQLITE_OK ){
 428     pCsr->iOffset = x[0];
 429     pCsr->szPage = (int)x[1];
 430   }
 431 }
 432
 433 /*
 434 ** Move a statvfs cursor to the next entry in the file.
 435 */
 436 static int statNext(sqlite3_vtab_cursor *pCursor){
 437   int rc;
 438   int nPayload;
 439   char *z;
 440   StatCursor *pCsr = (StatCursor *)pCursor;
 441   StatTable *pTab = (StatTable *)pCursor->pVtab;
 442   Btree *pBt = pTab->db->aDb[pCsr->iDb].pBt;
 443   Pager *pPager = sqlite3BtreePager(pBt);
 444
 445   sqlite3_free(pCsr->zPath);
 446   pCsr->zPath = 0;
 447
 448 statNextRestart:
 449   if( pCsr->aPage[0].pPg==0 ){
 450     rc = sqlite3_step(pCsr->pStmt);
 451     if( rc==SQLITE_ROW ){
 452       int nPage;
 453       u32 iRoot = (u32)sqlite3_column_int64(pCsr->pStmt, 1);
 454       sqlite3PagerPagecount(pPager, &nPage);
 455       if( nPage==0 ){
 456         pCsr->isEof = 1;
 457         return sqlite3_reset(pCsr->pStmt);
 458       }
 459       rc = sqlite3PagerGet(pPager, iRoot, &pCsr->aPage[0].pPg, 0);
 460       pCsr->aPage[0].iPgno = iRoot;
 461       pCsr->aPage[0].iCell = 0;
 462       pCsr->aPage[0].zPath = z = sqlite3_mprintf("/");
 463       pCsr->iPage = 0;
 464       if( z==0 ) rc = SQLITE_NOMEM_BKPT;
 465     }else{
 466       pCsr->isEof = 1;
 467       return sqlite3_reset(pCsr->pStmt);
 468     }
 469   }else{
 470
 471     /* Page p itself has already been visited. */
 472     StatPage *p = &pCsr->aPage[pCsr->iPage];
 473
 474     while( p->iCell<p->nCell ){
 475       StatCell *pCell = &p->aCell[p->iCell];
 476       if( pCell->iOvfl<pCell->nOvfl ){
 477         int nUsable;
 478         sqlite3BtreeEnter(pBt);
 479         nUsable = sqlite3BtreeGetPageSize(pBt) -
 480                         sqlite3BtreeGetReserveNoMutex(pBt);
 481         sqlite3BtreeLeave(pBt);
 482         pCsr->zName = (char *)sqlite3_column_text(pCsr->pStmt, 0);
 483         pCsr->iPageno = pCell->aOvfl[pCell->iOvfl];
 484         pCsr->zPagetype = "overflow";
 485         pCsr->nCell = 0;
 486         pCsr->nMxPayload = 0;
 487         pCsr->zPath = z = sqlite3_mprintf(
 488             "%s%.3x+%.6x", p->zPath, p->iCell, pCell->iOvfl
 489         );
 490         if( pCell->iOvfl<pCell->nOvfl-1 ){
 491           pCsr->nUnused = 0;
 492           pCsr->nPayload = nUsable - 4;
 493         }else{
 494           pCsr->nPayload = pCell->nLastOvfl;
 495           pCsr->nUnused = nUsable - 4 - pCsr->nPayload;
 496         }
 497         pCell->iOvfl++;
 498         statSizeAndOffset(pCsr);
 499         return z==0 ? SQLITE_NOMEM_BKPT : SQLITE_OK;
 500       }
 501       if( p->iRightChildPg ) break;
 502       p->iCell++;
 503     }
 504
 505     if( !p->iRightChildPg || p->iCell>p->nCell ){
 506       statClearPage(p);
 507       if( pCsr->iPage==0 ) return statNext(pCursor);
 508       pCsr->iPage--;
 509       goto statNextRestart; /* Tail recursion */
 510     }
 511     pCsr->iPage++;
 512     assert( p==&pCsr->aPage[pCsr->iPage-1] );
 513
 514     if( p->iCell==p->nCell ){
 515       p[1].iPgno = p->iRightChildPg;
 516     }else{
 517       p[1].iPgno = p->aCell[p->iCell].iChildPg;
 518     }
 519     rc = sqlite3PagerGet(pPager, p[1].iPgno, &p[1].pPg, 0);
 520     p[1].iCell = 0;
 521     p[1].zPath = z = sqlite3_mprintf("%s%.3x/", p->zPath, p->iCell);
 522     p->iCell++;
 523     if( z==0 ) rc = SQLITE_NOMEM_BKPT;
 524   }
 525
 526
 527   /* Populate the StatCursor fields with the values to be returned
 528   ** by the xColumn() and xRowid() methods.
 529   */
 530   if( rc==SQLITE_OK ){
 531     int i;
 532     StatPage *p = &pCsr->aPage[pCsr->iPage];
 533     pCsr->zName = (char *)sqlite3_column_text(pCsr->pStmt, 0);
 534     pCsr->iPageno = p->iPgno;
 535
 536     rc = statDecodePage(pBt, p);
 537     if( rc==SQLITE_OK ){
 538       statSizeAndOffset(pCsr);
 539
 540       switch( p->flags ){
 541         case 0x05:             /* table internal */
 542         case 0x02:             /* index internal */
 543           pCsr->zPagetype = "internal";
 544           break;
 545         case 0x0D:             /* table leaf */
 546         case 0x0A:             /* index leaf */
 547           pCsr->zPagetype = "leaf";
 548           break;
 549         default:
 550           pCsr->zPagetype = "corrupted";
 551           break;
 552       }
 553       pCsr->nCell = p->nCell;
 554       pCsr->nUnused = p->nUnused;
 555       pCsr->nMxPayload = p->nMxPayload;
 556       pCsr->zPath = z = sqlite3_mprintf("%s", p->zPath);
 557       if( z==0 ) rc = SQLITE_NOMEM_BKPT;
 558       nPayload = 0;
 559       for(i=0; i<p->nCell; i++){
 560         nPayload += p->aCell[i].nLocal;
 561       }
 562       pCsr->nPayload = nPayload;
 563     }
 564   }
 565
 566   return rc;
 567 }
 568
 569 static int statEof(sqlite3_vtab_cursor *pCursor){
 570   StatCursor *pCsr = (StatCursor *)pCursor;
 571   return pCsr->isEof;
 572 }
 573
 574 static int statFilter(
 575   sqlite3_vtab_cursor *pCursor,
 576   int idxNum, const char *idxStr,
 577   int argc, sqlite3_value **argv
 578 ){
 579   StatCursor *pCsr = (StatCursor *)pCursor;
 580   StatTable *pTab = (StatTable*)(pCursor->pVtab);
 581   char *zSql;
 582   int rc = SQLITE_OK;
 583   char *zMaster;
 584
 585   if( idxNum==1 ){
 586     const char *zDbase = (const char*)sqlite3_value_text(argv[0]);
 587     pCsr->iDb = sqlite3FindDbName(pTab->db, zDbase);
 588     if( pCsr->iDb<0 ){
 589       sqlite3_free(pCursor->pVtab->zErrMsg);
 590       pCursor->pVtab->zErrMsg = sqlite3_mprintf("no such schema: %s", zDbase);
 591       return pCursor->pVtab->zErrMsg ? SQLITE_ERROR : SQLITE_NOMEM_BKPT;
 592     }
 593   }else{
 594     pCsr->iDb = pTab->iDb;
 595   }
 596   statResetCsr(pCsr);
 597   sqlite3_finalize(pCsr->pStmt);
 598   pCsr->pStmt = 0;
 599   zMaster = pCsr->iDb==1 ? "sqlite_temp_master" : "sqlite_master";
 600   zSql = sqlite3_mprintf(
 601       "SELECT 'sqlite_master' AS name, 1 AS rootpage, 'table' AS type"
 602       "  UNION ALL  "
 603       "SELECT name, rootpage, type"
 604       "  FROM \"%w\".%s WHERE rootpage!=0"
 605       "  ORDER BY name", pTab->db->aDb[pCsr->iDb].zDbSName, zMaster);
 606   if( zSql==0 ){
 607     return SQLITE_NOMEM_BKPT;
 608   }else{
 609     rc = sqlite3_prepare_v2(pTab->db, zSql, -1, &pCsr->pStmt, 0);
 610     sqlite3_free(zSql);
 611   }
 612
 613   if( rc==SQLITE_OK ){
 614     rc = statNext(pCursor);
 615   }
 616   return rc;
 617 }
 618
 619 static int statColumn(
 620   sqlite3_vtab_cursor *pCursor,
 621   sqlite3_context *ctx,
 622   int i
 623 ){
 624   StatCursor *pCsr = (StatCursor *)pCursor;
 625   switch( i ){
 626     case 0:            /* name */
 627       sqlite3_result_text(ctx, pCsr->zName, -1, SQLITE_TRANSIENT);
 628       break;
 629     case 1:            /* path */
 630       sqlite3_result_text(ctx, pCsr->zPath, -1, SQLITE_TRANSIENT);
 631       break;
 632     case 2:            /* pageno */
 633       sqlite3_result_int64(ctx, pCsr->iPageno);
 634       break;
 635     case 3:            /* pagetype */
 636       sqlite3_result_text(ctx, pCsr->zPagetype, -1, SQLITE_STATIC);
 637       break;
 638     case 4:            /* ncell */
 639       sqlite3_result_int(ctx, pCsr->nCell);
 640       break;
 641     case 5:            /* payload */
 642       sqlite3_result_int(ctx, pCsr->nPayload);
 643       break;
 644     case 6:            /* unused */
 645       sqlite3_result_int(ctx, pCsr->nUnused);
 646       break;
 647     case 7:            /* mx_payload */
 648       sqlite3_result_int(ctx, pCsr->nMxPayload);
 649       break;
 650     case 8:            /* pgoffset */
 651       sqlite3_result_int64(ctx, pCsr->iOffset);
 652       break;
 653     case 9:            /* pgsize */
 654       sqlite3_result_int(ctx, pCsr->szPage);
 655       break;
 656     default: {          /* schema */
 657       sqlite3 *db = sqlite3_context_db_handle(ctx);
 658       int iDb = pCsr->iDb;
 659       sqlite3_result_text(ctx, db->aDb[iDb].zDbSName, -1, SQLITE_STATIC);
 660       break;
 661     }
 662   }
 663   return SQLITE_OK;
 664 }
 665
 666 static int statRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
 667   StatCursor *pCsr = (StatCursor *)pCursor;
 668   *pRowid = pCsr->iPageno;
 669   return SQLITE_OK;
 670 }
 671
 672 /*
 673 ** Invoke this routine to register the "dbstat" virtual table module
 674 */
 675 int sqlite3DbstatRegister(sqlite3 *db){
 676   static sqlite3_module dbstat_module = {
 677     0,                            /* iVersion */
 678     statConnect,                  /* xCreate */
 679     statConnect,                  /* xConnect */
 680     statBestIndex,                /* xBestIndex */
 681     statDisconnect,               /* xDisconnect */
 682     statDisconnect,               /* xDestroy */
 683     statOpen,                     /* xOpen - open a cursor */
 684     statClose,                    /* xClose - close a cursor */
 685     statFilter,                   /* xFilter - configure scan constraints */
 686     statNext,                     /* xNext - advance a cursor */
 687     statEof,                      /* xEof - check for end of scan */
 688     statColumn,                   /* xColumn - read data */
 689     statRowid,                    /* xRowid - read data */
 690     0,                            /* xUpdate */
 691     0,                            /* xBegin */
 692     0,                            /* xSync */
 693     0,                            /* xCommit */
 694     0,                            /* xRollback */
 695     0,                            /* xFindMethod */
 696     0,                            /* xRename */
 697     0,                            /* xSavepoint */
 698     0,                            /* xRelease */
 699     0,                            /* xRollbackTo */
 700   };
 701   return sqlite3_create_module(db, "dbstat", &dbstat_module, 0);
 702 }
 703 #elif defined(SQLITE_ENABLE_DBSTAT_VTAB)
 704 int sqlite3DbstatRegister(sqlite3 *db){ return SQLITE_OK; }
 705 #endif /* SQLITE_ENABLE_DBSTAT_VTAB */