\documentclass{article}
\input{6824-preamble}

\begin{document}
\psetnum{16}
\date{2005/04/28}

\begin{pset}
  Suppose server $S_1$ crashes after it modifies an inode, and after
  server $S_2$ later modifies the same inode. $S_1$'s log will contain an
  entry due to the change, but it will not be replayed at recovery
  time. In order for $S_2$ to have modified the same inode, it would
  need to acquire the lock from $S_1$, and $S_1$ cannot release the
  lock without writing the update to Petal. Then we know that the
  log entry will not be replayed because it describes an update that
  has already been completed, and the version numbers on each metadata
  block prevent the update from being reapplied.
\end{pset}
\end{document}
