Make No. of Transport Threads == Available CPUs (#56488) #56780
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We never do any file IO or other blocking work on the transport threads so no tangible benefit can be derived from using more threads than CPUs for IO. There are however significant downsides to using more threads than necessary with Netty in particular. Since we use the default setting for `io.netty.allocator.useCacheForAllThreads` which is `true` we end up using up to `16MB` of thread local buffer cache for each transport thread. Meaning we potentially waste CPUs * 16MB of heap for unnecessary IO threads in addition to obvious inefficiencies of artificially adding extra context switches.
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We never do any file IO or other blocking work on the transport threads
so no tangible benefit can be derived from using more threads than CPUs
for IO.
There are however significant downsides to using more threads than necessary
with Netty in particular. Since we use the default setting for
io.netty.allocator.useCacheForAllThreadswhich istruewe end upusing up to
16MBof thread local buffer cache for each transport thread.Meaning we potentially waste CPUs * 16MB of heap for unnecessary IO threads in addition to obvious inefficiencies of artificially adding extra context switches.
backport of #56488