docs: add default threads count about NioEventLoopGroup

[brido4125]

add NioEventLoopGroup default threads counts in AbstractRedisClient javadoc.

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[tishun]

Hey @brido4125 ,
can we take a step back and discuss the issue.

I assume you found it hard to understand the defaults, correct? Would it make sense to add this to the documentation instead (not sure how many users dig in the source code to that level) ?

[brido4125]

I assume you found it hard to understand the defaults, correct?

Yes, exactly what i intended.
I wanted to find default value for NioEventLoopGroup
because the default value for EpollEventLoopGroup is mentioned with same paragraph.

Would it make sense to add this to the documentation instead (not sure how many users dig in the source code to that level) ?

I agree.
where can i find the docs about RedisCilent or NioEventLoopGroup config?
(I cannot find proper documentation in lettuce/docs dir)

[tishun]

Yes, exactly what i intended. I wanted to find default value for NioEventLoopGroup because the default value for EpollEventLoopGroup is mentioned with same paragraph.

This comment is actually quite ancient (comes from the year of 2015) and does not seem to be entirely correct, as per the current code base. I would rephrase the entire JavaDoc with something less specific, because the AbstractRedisClient is no longer involved in configuring the event loop threads. Instead the DefaultClientResources has all this logic in it.

The number of threads for both I/O and computation are selected in the following way:

• any setting in the ClientOptions takes first precedence, otherwise we fallback to defaults
• if there is an environment variable setting for io.netty.eventLoopThreads we use it as default, otherwise ...
• ... we take the number of available processors, retrieved by Runtime.getRuntime().availableProcessors()
• in any case if the chosen number is less than the minimum, which is 2 threads, then we use the minimum

So the setting for both I/O and computation threads are based on the presence and value of the above settings.

I agree. where can i find the docs about RedisCilent or NioEventLoopGroup config? (I cannot find proper documentation in lettuce/docs dir)

I think the best I can find was https://redis.github.io/lettuce/advanced-usage/#configuration-settings
However it does not mention all the details. It also seems to be outdated and states that the minimum is 3 and not 2, which was changed in #1278