After a certain number of searches, thawing the search history cookie (line ~296 of C4/Auth.pm) can cause an "Out of memory" error, causing all OPAC scripts to stop working. This seems to occur after a certain number of searches, but does not seem to be related to corruption or truncation due to the max cookie size. The current workaround is to disable OPAC search history (the EnableOpacSearchHistory syspref).
This should be fixed by the patch to bug 10657, which replaces Storable with JSON for serializing the search history.
(In reply to Galen Charlton from comment #1) > This should be fixed by the patch to bug 10657, which replaces Storable with > JSON for serializing the search history. Confirmed, should be fixed.