Why should Redis avoid executing commands with high time complexity

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Avoid executing commands with high time complexity

We know that Redis executes commands "in a single thread". Executing commands with high time complexity is likely to block other requests.

Complex commands are related to the number of elements. There are usually two scenarios.

Too many elements, consuming IO resources. For example, HGETALL, LRANGE, the time complexity is O (N).

The calculation is too complex and consumes CPU resources. For example, ZUNIONSTORE, the time complexity is O (N) + O (M log (M))

The Redis official manual, which marks the time complexity of command execution. It is recommended that you check the manual and pay attention to the time complexity before using unfamiliar commands.

In real business, you should try to avoid commands with high time complexity. If you have to, there are two suggestions.

Ensure that the number of elements for the operation is as small as possible.

Separation of reading and writing. Complex commands are usually read requests and can be executed on the "slave" node.

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