Recently, I ran into an error while attempting to install a PECL package on a Redhat 5.3 64bit server.

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Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to allocate 23040 bytes) in /usr/share/pear/PEAR/Builder.php on line 263
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I checked the memory limit setting in /etc/php.ini and it was set for 16M so that wasn't the problem. This is happening because PECL requires more memory on a 64bit box than a 32bit one. Incidentally, this works fine on 32bit OS's.

There are a couple of ways to get around this. The first would be to place the following at the top of the /usr/share/pear/pearcmd.php file:

ini_set('memory_limit', '16M');

Alternatively, you could could add the following to /usr/bin/pecl:

-d memory_limit=16M

16M should be plenty. However, if you still don't have enough memory then up the number to 32M. If that isn't enough, something else is going on.