I have multiple instances of APC running on my server with similar configurations (albeit with different cache sizes. However, one of the instances is performing extremely poorly, and I have no idea why (100% cache fragmentation, high miss rate).
The runtime settings I'm using are as follows (pretty much out of the box):
apc.cache_by_default 1 apc.canonicalize 1 apc.coredump_unmap 0 apc.enable_cli 0 apc.enabled 1 apc.file_md5 0 apc.file_update_protection 2 apc.filters apc.gc_ttl 3600 apc.include_once_override 0 apc.lazy_classes 0 apc.lazy_functions 0 apc.max_file_size 1M apc.mmap_file_mask apc.num_files_hint 1000 apc.preload_path apc.report_autofilter 0 apc.rfc1867 0 apc.rfc1867_freq 0 apc.rfc1867_name APC_UPLOAD_PROGRESS apc.rfc1867_prefix upload_ apc.rfc1867_ttl 3600 apc.shm_segments 1 apc.shm_size 10M apc.slam_defense 1 apc.stat 1 apc.stat_ctime 0 apc.ttl 0 apc.use_request_time 1 apc.user_entries_hint 4096 apc.user_ttl 0 apc.write_lock 1
APC is version 3.1.6, PHP is 5.3.3-1ubuntu9.5. I've tried restarting Apache multiple times, so this isn't a freak instance.
The instance with problems is simply running Wordpress with a few plugins installed. All other instances (~4) on the server are running perfectly fine with almost 100% hit rates and 0% fragmentation; for example this instance is holding a website built using the Symfony framework.
Any help would be much appreciated; I haven't had much experience with APC and was hoping for it to be an out-of-the-box speed boost ;).