SQLite

#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
int pagerUseWal(Pager *pPager){
  return (pPager->pWal!=0);
}
#else
# define pagerUseWal(x) 0
# define pagerRollbackWal(x) 0
# define pagerWalFrames(v,w,x,y,z) 0
# define pagerOpenWalIfPresent(z) SQLITE_OK

    ** backup in progress needs to be restarted.
    */
    sqlite3BackupRestart(pPager->pBackup);
  }else{
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
       // rc = pagerWalFrames(pPager, pList, pPager->dbSize, 1, (pPager->fullSync ? pPager->sync_flags : 0)
        rc = pagerWalFrames(pPager, pList, pPager->dbSize, 1, 0        

        );
      }
      if( rc==SQLITE_OK ){
        sqlite3PcacheCleanAll(pPager->pPCache);
      }
    }else{
      /* The following block updates the change-counter. Exactly how it

      }
    }
    if( eMode==PAGER_JOURNALMODE_QUERY && pId2->n==0 ){
      /* Convert "PRAGMA journal_mode" into "PRAGMA main.journal_mode" */
      iDb = 0;
      pId2->n = 1;
    }
    if (eMode == PAGER_JOURNALMODE_WAL) {
      db->flags |= SQLITE_FullFSync;
      sqlite3VdbeAddOp2(v, OP_Expire, 0, 0);
    }
    for(ii=db->nDb-1; ii>=0; ii--){
      if( db->aDb[ii].pBt && (ii==iDb || pId2->n==0) ){
        sqlite3VdbeUsesBtree(v, ii);
        sqlite3VdbeAddOp3(v, OP_JournalMode, ii, 1, eMode);
      }
    }
    sqlite3VdbeAddOp2(v, OP_ResultRow, 1, 1);

    }else if( sqlite3GetInt32(argv[1], &pIndex->tnum)==0 ){
      corruptSchema(pData, argv[0], "invalid rootpage");
    }
  }
  return 0;
}

extern int pagerUseWal(Pager *p);

/*
** Attempt to read the database schema and initialize internal
** data structures for a single database file.  The index of the
** database file is given by iDb.  iDb==0 is used for the main
** database.  iDb==1 should never be used.  iDb>=2 is used for
** auxiliary databases.  Return one of the SQLITE_ error codes to
** indicate success or failure.

    pDb->pSchema->file_format = 1;
  }
  if( pDb->pSchema->file_format>SQLITE_MAX_FILE_FORMAT ){
    sqlite3SetString(pzErrMsg, db, "unsupported file format");
    rc = SQLITE_ERROR;
    goto initone_error_out;
  }
#ifndef SQLITE_OMIT_WAL
  if( pagerUseWal((Pager *)pDb->pBt) ){
    db->flags |= SQLITE_FullFSync;
  }
#endif
  
  /* Ticket #2804:  When we open a database in the newer file format,
  ** clear the legacy_file_format pragma flag so that a VACUUM will
  ** not downgrade the database and thus invalidate any descending
  ** indices that the user might have created.
  */
  if( iDb==0 && meta[BTREE_FILE_FORMAT-1]>=4 ){
    db->flags &= ~SQLITE_LegacyFileFmt;

   && (rc = walLockExclusive(pWal, WAL_READ_LOCK(0), 1))==SQLITE_OK
  ){
    i64 nSize;                    /* Current size of database file */
    u32 nBackfill = pInfo->nBackfill;

    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }

    /* If the database file may grow as a result of this checkpoint, hint
    ** about the eventual size of the db file to the VFS layer. 
    */
    if( rc==SQLITE_OK ){
      i64 nReq = ((i64)mxPage * szPage);

    /* If work was actually accomplished... */
    if( rc==SQLITE_OK ){
      if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
        i64 szDb = pWal->hdr.nPage*(i64)szPage;
        testcase( IS_BIG_INT(szDb) );
        rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
        if( rc==SQLITE_OK && sync_flags ){
          rc = sqlite3OsSync(pWal->pDbFd, sync_flags);
        }
      }
      if( rc==SQLITE_OK ){
        pInfo->nBackfill = mxSafeFrame;
      }
    }