Signatures generation performance improvements

[jimmydorry]

They consume too much of the resources. It would be nice if I could just drop them completely.

It's possible that one of the signature libraries we rely is broken too.

I either cause a lot of I/O waste by caching the responses to disk (100KB per request), or I consume PHP worker slots by holding in memory and waiting for the complete request. They can also take up to 12 seconds to generate.

[jimmydorry]

The temporary fix is to set error level to error in nginx, and disable caching. Sigs appear to take 10seconds to generate around this time of the day.

[jimmydorry]

• [ ] Don't make signatures on the fly. Just do the logging, and then readfile().
• [ ] If a signature is brand new, only display the default signature base saying generation may take a few hours.
• [ ] Make a sig queue, that queues signatures for re-generation if they are older than 4 hours by filetime(). Make sure to put new sigs as the highest priority.
• [ ] Set header to expire sig image after 4 hours. Downloading the sig after it is stale should have an expiry header of 2 hours from the time it is accessed.
• [ ] Have a cron run every hour to re-generate stale sigs, making sure to lock so multiple crons don't run.

[jimmydorry]

The two bottlenecks for signature generation are getting data from DB and grabbing the user's avatar