SQLite

  /* If page 1 of the database is not writable, then no pages were allocated
  ** or freed by this transaction. In this case no special handling is 
  ** required. Otherwise, if page 1 is dirty, proceed.  */
  BtreePtrmap *pMap = pBt->pMap;
  Pgno iTrunk = get4byte(&p1[32]);
  Pgno nPage = btreePagecount(pBt);

  u32 nFree = get4byte(&p1[36]);

  assert( sqlite3PagerIsUnlocked(pPager) );
  assert( pBt->pMap );
  rc = sqlite3PagerUpgradeSnapshot(pPager, pPage1->pDbPage);
  assert( p1==pPage1->aData );

          if( iTrunk==0 ){
            put4byte((u8*)pTrunk->pData, iHTrunk);
          }
          sqlite3PagerUnref(pTrunk);
        };
      }

      if( nHPage<(pMap->iFirst-1) ){
        /* The database consisted of (pMap->iFirst-1) pages when the current
        ** unlocked transaction was opened. And an unlocked transaction may
        ** not be executed on an auto-vacuum database - so the db should 
        ** not have shrunk since the transaction was opened. Therefore nHPage

        ** should be set to (pMap->iFirst-1) or greater. */
        rc = SQLITE_CORRUPT_BKPT;
      }else{
        /* The current transaction allocated pages pMap->iFirst through
        ** nPage (inclusive) at the end of the database file. Meanwhile,
        ** other transactions have allocated (iFirst..nHPage). So move
        ** pages (iFirst..MIN(nPage,nHPage)) to (MAX(nPage,nHPage)+1).
        */
        Pgno iLast = MIN(nPage, nHPage);    /* Last page to move */
        Pgno iPg;
        Pgno nCurrent;                      /* Current size of db */

        nCurrent = MAX(nPage, nHPage);
        for(iPg=pMap->iFirst; iPg<=iLast && rc==SQLITE_OK; iPg++){
          MemPage *pPg = 0;
          Pgno iNew;              /* New page number for pPg */
          PtrmapEntry *pEntry;    /* Pointer map entry for page iPg */

          pEntry = &pMap->aPtr[iPg - pMap->iFirst];
          if( pEntry->eType==PTRMAP_FREEPAGE ){
            MemPage *pFree = 0;
            Pgno dummy;
            rc = allocateBtreePage(pBt, &pFree, &dummy, iPg, BTALLOC_EXACT);
            releasePage(pFree);
            assert( rc!=SQLITE_OK || dummy==iPg );
          }else{
            btreeGetPage(pBt, iPg, &pPg, 0);
            assert( sqlite3PagerIswriteable(pPg->pDbPage) );
            assert( sqlite3PagerPageRefcount(pPg->pDbPage)==1 );
            iNew = ++nCurrent;
            rc = relocatePage(pBt, pPg, pEntry->eType, pEntry->parent, iNew, 1);
            releasePageNotNull(pPg);
          }
        }
        sqlite3PagerSetDbsize(pPager, nCurrent);

        nFree = get4byte(&p1[36]);
        nFinal = MAX(nCurrent-nFree, nHPage);

        for(iPg=nFinal+1; rc==SQLITE_OK && iPg<nCurrent; iPg++){
          Pgno iNew;              /* New page number for pPg */
          MemPage *pFree;
          PtrmapEntry *pEntry;    /* Pointer map entry for page iPg */

          pEntry = &pMap->aPtr[iPg - pMap->iFirst];
          if( pEntry->eType==PTRMAP_FREEPAGE ){
            rc = allocateBtreePage(pBt, &pFree, &iNew, iPg, BTALLOC_EXACT);
            releasePage(pFree);
          }else{
            rc = allocateBtreePage(pBt, &pFree, &iNew, nFinal, BTALLOC_LE);
            releasePage(pFree);
            if( rc==SQLITE_OK ){
              MemPage *pPg = 0;
              btreeGetPage(pBt, iPg, &pPg, 0);
              rc = relocatePage(pBt, pPg, pEntry->eType, pEntry->parent,iNew,1);
            }
          }
        }
        put4byte(&p1[28], nFinal);
      }
    }
    sqlite3PagerSetDbsize(pPager, nFinal);
  }

  u32 n;     /* Number of pages on the freelist */
  u32 k;     /* Number of leaves on the trunk of the freelist */
  MemPage *pTrunk = 0;
  MemPage *pPrevTrunk = 0;
  Pgno mxPage;     /* Total size of the database file */

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( eMode==BTALLOC_ANY || (nearby>0 && REQUIRE_PTRMAP ) );


  pPage1 = pBt->pPage1;
  mxPage = btreePagecount(pBt);
  /* EVIDENCE-OF: R-05119-02637 The 4-byte big-endian integer at offset 36
  ** stores stores the total number of pages on the freelist. */
  n = get4byte(&pPage1->aData[36]);
  testcase( n==mxPage-1 );
  if( sqlite3PagerIsUnlocked(pBt->pPager)==0 && n>=mxPage ){

          if( eType==PTRMAP_FREEPAGE ){
            searchList = 1;
          }
        }
      }else{
        searchList = 1;
      }


    }else if( eMode==BTALLOC_LE ){
      searchList = 1;
    }


    /* Decrement the free-list count by 1. Set iTrunk to the index of the
    ** first free-list trunk page. iPrevTrunk is initially 1.
    */
    put4byte(&pPage1->aData[36], n-1);

    /* The code within this loop is run only once if the 'searchList' variable

  do_test 1.$tn.1 {
    sql1 {
      PRAGMA journal_mode = wal;
      CREATE TABLE t1(x);
      CREATE TABLE t2(y);
    }
  } {wal}
  do_test 1.$tn.5 { sql3 { PRAGMA integrity_check } } {ok}

  # Test that an UNLOCKED transaction that allocates/frees no pages does
  # not conflict with a transaction that does allocate pages.
  do_test 1.$tn.2  {
    sql1 { 
      BEGIN UNLOCKED;
        INSERT INTO t1 VALUES(4);
    }
    sql2 {
      INSERT INTO t2 VALUES(randomblob(1500));
    }
    sql1 {
      COMMIT;
    }
  } {}
  do_test 1.$tn.5 { sql3 { PRAGMA integrity_check } } {ok}
  
  # But that an UNLOCKED transaction does conflict with a transaction
  # that modifies the db schema.
  do_test 1.$tn.3  {
    sql1 {
      BEGIN UNLOCKED;
        INSERT INTO t1 VALUES(5);
    }
    sql2 {
      CREATE TABLE t3(z);
    }
    list [catch { sql1 COMMIT } msg] $msg
  } {1 {database is locked}}
  do_test 1.$tn.5 { sql3 { PRAGMA integrity_check } } {ok}
  
  # Test that an UNLOCKED transaction that allocates at least one page 
  # does not conflict with a transaction that allocates no pages.
  do_test 1.$tn.4  {
    sql1 { 
      ROLLBACK;
      BEGIN UNLOCKED;
        INSERT INTO t1 VALUES(randomblob(1500));
    }
    sql2 {
      INSERT INTO t2 VALUES(8);
    }
    breakpoint
    sql1 {
      COMMIT;
    }
  } {}

  do_test 1.$tn.5 { sql3 { PRAGMA integrity_check } } {ok}
}