Basic Troubleshooting: Difference between revisions
→Tail Latency
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= Tail Latency =
Source [http://highscalability.com/blog/2012/3/12/google-taming-the-long-latency-tail-when-more-machines-equal.html highscalability.com], [https://accelazh.github.io/storage/Tail-Latency-Study accelazh.github.io]
*Imagine a client making a request of a single web server.
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Slow processing code
Other Reasons:
Overprovisioned VMs
Many OS images being forked from a small shared base
A large request may be pegging your CPU/network/disk, and make the others queuing up.
something went wrong as a dead loop stuck your cpu.
*The latency percentile has low, middle, and tail parts.
*To reduce the low, middle parts: Provisioning more resources, cut and parallelize the tasks, eliminate “head-of-line” blocking, and caching will help.
*To reduce the tail latency: The basic idea is hedging.
*Even we’ve parallelized the service, the slowest instance will determine when our request is done.
*Code freezes--interrupt, context switch, cache buffer flush to disk, garbage collection, reindexing the database
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