Yes, apc.stat is 1 at my server.
I have a lot Fragmentation (12%), but I guess it's because of my crappy Wordpress. Is there a way to separate APC from different domains on the same VPS? I mean, showing different stats for each on of my domains on the server.
What are the advantages? I read many good reviews on XCache or APC + memcached, but I'm not sure if memcached has any advantage for a relatively small boards with 500K posts/2000 visits a day/850MB SQL
Performance. Zend Optimizer+ has a consistent performance edge over APC, which, depending on the code, can range between 5 and 20% in terms of requests/second. See Benchmarks section below.
Availability for new PHP versions. Optimizer+ is typically fully compatible with PHP releases even before they come out; While this advantage was rarely realized because of the closed-source nature of the component, once open-source, both Zend and the community will help ensure that it’s always fully compatible with every element of the PHP language, avoiding any lags.
Reliability. Optimizer+ has optional corruption detection capabilities that can prevent a server-wide crash in case of data corruption (e.g. from a faulty implementation of a PHP function in C). This handles one of the very few downsides of using a shared-memory-based-opcode-cache - introducing a shared resource that - if corrupted - could bring down an entire server.
Better compatibility. We strived to make Optimizer+ work with any and all constructs supported by PHP, in exactly the same way they’d behave without it.
Advantages of APC over Optimizer+
Has a data caching API. APC has a data caching API which Optimizer+ does not have.
APC can reclaim memory of old invalidated scripts. APC uses a memory manager and can reclaim memory associated with a script that is no longer in use; Optimizer+ works differently, and marks such memory as ‘dirty’, but never actually reclaims it. Once the dirty percentage climbs above a configurable threshold - Optimizer+ restarts itself. Note that this behavior has both stability advantages and disadvantages.
memcached should be configured on the server level or/and Xenforo level? I saw some lines that are one should add to the config.php file once memcached installed, but other then that, is there anything else?
I guess data cache isn't relevant for small boards? (500K posts)?