My cache is 200000 MB large, and the problem happens clearly when the cache gets full. I can see from AOLServer stats the following info:
Cache Max Current Entries Flushes Hits Misses Hit Rate
xowiki_cache 200000 2026 6 0 110 106 50%
xotcl_object_type_cache 10000 346 37 35809 92407 35846 72%
xotcl_object_cache 400000 19591 16 0 6152 16 99%
util_memoize 200000 199939 2852 7557 1109321 26009 97%
secret_tokens 32768 600 15 0 300 15 95%
nsfp:ct-gcie 5120000 934418 137 0 1557 137 91%
nsfp: 5120000 0 0 0 0 0 0%
ns:dnshost 100 0 0 0 0 0 0%
ns:dnsaddr 100 5 5 0 230 5 97%
ds_page_bits 10000000 0 0 0 0 0 0%
db_cache_pool 200000 20 2 0 7841 2 99%
When the cache gets close to the limit and the system try to reload it, it fails and the reloading proccess lasts forever.