scale xymatrix diagram

Question

I have a commutative diagram similar to the one below that is way too big to fit on the page. Is there a way to scale the diagram down so that it fits? I read that this could be done using the tikz package, but was wondering if it can also be done using xymatrix. It would be nice if there was a way to have the commutative diagram scale automatically to fit the page margins.

\documentclass[reqno]{amsart} 
\usepackage[all,cmtip]{xy}
\begin{document} 
\begin{equation*}
\xymatrix{
0 \ar[r] & \underset{w \in S_{\infty}}{\bigoplus} AAAAAAAAAAAAAAAAA \ar[r]^-{f'} & BBBBBBBBBB^{\Gamma} \ar[r]^-{g'} & CCCCCCCCCCCCCCCC \ar[r] & 0\\
0 \ar[r] & AAAAAAAAAAAAAAAA \ar[u]^{\psi} \ar[r]^{f} & BBBBBBBBBB \ar[u]^{\psi'} \ar[r]^{g} & CCCCCCCCCC \ar[u]^{\psi''} \ar[r] & 0\\
}
\end{equation*}
\end{document}

Answer 1

Resizing should be the last resort.

\documentclass[reqno]{amsart}
\usepackage[all,cmtip]{xy}
\usepackage{graphicx}

\usepackage{showframe} % just for debugging

\begin{document}
\begin{equation*}
\resizebox{\displaywidth}{!}{%
\xymatrix{
  0 \ar[r] &
  \mathop{\smash{\bigoplus\limits_{w \in S_{\infty}}}} AAAAAAAAAAAAAAAAA
    \ar[r]^-{f'} & BBBBBBBBBB^{\Gamma} \ar[r]^-{g'} &
  CCCCCCCCCCCCCCCC \ar[r] &
  0\\
  0 \ar[r] &
  AAAAAAAAAAAAAAAA \ar[u]^{\psi} \ar[r]^{f} &
  BBBBBBBBBB \ar[u]^{\psi'} \ar[r]^{g} &
  CCCCCCCCCC \ar[u]^{\psi''} \ar[r] &
  0
}}
\end{equation*}
\end{document}