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I/O scheduler tunables

fifo_batch: This parameter controls the maximum number of requests per batch.It tunes the balance between per-request latency and aggregate throughput. When low latency is the primary concern, smaller is better (where a value of 1 yields first-come first-served behavior). Increasing fifo_batch generally improves throughput, at the cost of latency variation. The default is 16. front_merges: A request that enters the scheduler is possibly contiguous to a request that is already on the queue. Either it fits in the back of that request, or it fits at the front. Hence it’s called either a back merge candidate or a front merge candidate. Typically back merges are much more common than front merges. You can set this tunable to 0 if you know your workload will never generate front merges. Otherwise leave it at its default value 1. read_expire: In all 3 schedulers, there is some form of deadline to service each Read Request. The focus is read latencies. When a read request first enters the io scheduler, it is assigned a deadline that is the current time + the read_expire value in units of milliseconds. The default value is 500 ms. write_expire: Similar to Read_Expire, this applies only to the Write Requests. The default value is 5000 ms. writes_starved: Typically more attention is given to the Read requests over write requests. But this can’t go on forever. So after the expiry of this value, some of the pending write requests get the same priority as the Reads. Default value is 1. This tunable controls how many read batches can be processed before processing a single write batch. The higher this is set, the more preference is given to reads.

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Nginx 性能调优

NGINX is well known as a high performance load balancer, cache and web server, powering over 40% of the busiest websites in the world.  Most of the default NGINX and Linux settings work well for most use cases, but it can be necessary to do some tuning to achieve optimal performance.  This blog post will discuss some of the NGINX and Linux settings to consider when tuning a system.  There are many settings available, but for this post we will cover the few settings recommended for most users to consider adjusting.  The settings not covered in this post are ones that should only be considered by those with a deep understanding of NGINX and Linux, or after a recommendation by the NGINX support or professional services teams.  NGINX professional services has worked with some of the world’s busiest websites to tune NGINX to get the maximum level of performance and are available to work with any customer who needs to get the most out of their system.

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