HHVM notes

  • Impressive throughput improvements (>100%) with the app that I am working on.
  • phpinfo() doesn’t output what you would expect.
  • xhprof output_dir doesn’t get read from ini files, need to set that up in the constructor of XHProfRuns_Default.
  • Set hhvm.server.thread_count to a high value (>=MaxRequestWorkers), otherwise a few slow MySQL queries could bring the server to halt, minimal doc here: HHVM server architecture (worker thread => hhvm.server.thread_count). Suggest to keep it higher while JITing is happening.
  • If using Newrelic, tough luck!
    Unofficial Newrelic HHVM extension uses XHProf internally, so cannot get any data out of your own XHProf usage.
    The extension above relies on agent SDK that has no support for MySQL slow traces.
    Very low MySQL time in transactions.
    Strange traces in transactions.
  • CGI differences (apache_getenv not available use $_SERVER, SCRIPT_NAME will not be the same as REQUEST_URI).
  • Use realpath in imageftbox, relative paths for fonts don’t work.
  • Use Apache 2.4 as it has FastCGI support.
  • hhvm.log.header = true to have datetime in hhvm log.
  • HHVM log will also contain slow sql.
  • .hhbc was getting very huge, turned out it was due to Smarty file caching being enabled (the cached files were themselves php files that HHVM was compiling).
  • .hhbc file is sqlite(3) file that one can query (that is how I worked out the above).
  • High timeout values in memcached was leading to very high System CPU usage.
  • @ wasn’t suppressing (this could be Newrelic related)
  • Friendly folks in the hhvm IRC channel (get link from HHVM homepage), need to be online during daytime in the US.