Can I use apc opcode cache if I can (not must) have unique content for each visitor on same page? I'm not sure I understand how opcode working. If only save php result to cache and serving it like "html", then it's useless for me. I definitely need to run sql queries on each pageview. Or it's any better way how to optimize php? App have very high-load - about 1000 pageviews per second. It run on nginx + php-fpm.
Yes, you can. APC caches the program, not its' result. So, the code will be executed each time, just in "optimised" way.