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File Manager (cont)

Access to a block of data proceeds (roughly) as follows: 

// pageID set from pg_catalog tables
// buffer obtained from Buffer pool
getBlock(BufferTag pageID, Buffer buf)
{
   File fid;  off_t offset;  int fd;
   (fid, offset) = findBlock(pageID)
   fd = VfdCache[fid].fd;
   lseek(fd, offset, SEEK_SET)
   VfdCache[fid].seekPos = offset;
   nread = read(fd, buf, BLOCKSIZE)
   if (nread < BLOCKSIZE) ... we have a problem
}

BLOCKSIZE is a global configurable constant (default: 8192)