Search too slow periodically

[jacobfan]

Haoyaoshi clients found that certain search queries are very slow periodically.

Cause: The cache expires periodically. And if the search frequency is very high and the query very expensive, there would be too much ES query issued at the same time. So the client would timeout.

Current status: the client's change of timeout takes effect this morning, and the problem disappeared temporailly.

@sunliwen

[jacobfan]

I've added a custom access log to record to the request time and upstream time. (nginx_poco_access.custom.log)