4 ms·

If you used to tune JVM only, that might be interesting. Most often the Java code is what being tuned - to the point where there is no point to use Java - with

by snaky 8y ago

If you used to tune JVM only, that might be interesting. Most often the Java code is what being tuned - to the point where there is no point to use Java - with (almost) no gc, off-the-heap memory allocations and all that jazz.

dnomad 8y ago
This doesn't make much sense. Using object pools and and off-heap data structures doesn't warp the code that much, if at all. You still end up with pretty much all clean, simple Java code. I've seen (10+ years old) low-latency Java apps where people avoid using any OO (ie everything is static methods)... and even then the code was still often easier to maintain and understand than equivalent C++ applications. Nobody does this any more anyways.
branchless 8y ago
There are more java developers you can educate to do this than good c++ dev. Plus the tooling is better in java.
phakding 8y ago
It's not either/or. Everything needs to be tuned to achieve the final latency requirements. This includes tuning java code to eliminate creating "garbage", immutable string objects mostly, unnecessary object creation, creating short lived objects compared to long lived etc. The other part right sizing jvm generational partitions, using right gc algo etc. Next part would be to find out the code path with lowest latency requirement and making it hot/jitting. Even next part would be to tune OS for things like thread pinning etc etc. You can go further and tune the network layer. Every little thing counts. You can go even further and employ what's called mechanical sympathy (https://mechanical-sympathy.blogspot.com/ https://mechanical-sympathy.blogspot.com/) and write your code in a way that makes it easier for the processor to process faster. I've never worked with application that use off-heap allocations or no-gc requirements.

4 ms·

If you used to tune JVM only, that might be interesting. Most often the Java code is what being tuned - to the point where there is no point to use Java - with

by snaky 8y ago

dnomad 8y ago
This doesn't make much sense. Using object pools and and off-heap data structures doesn't warp the code that much, if at all. You still end up with pretty much all clean, simple Java code. I've seen (10+ years old) low-latency Java apps where people avoid using any OO (ie everything is static methods)... and even then the code was still often easier to maintain and understand than equivalent C++ applications. Nobody does this any more anyways.
branchless 8y ago
There are more java developers you can educate to do this than good c++ dev. Plus the tooling is better in java.
phakding 8y ago
It's not either/or. Everything needs to be tuned to achieve the final latency requirements. This includes tuning java code to eliminate creating "garbage", immutable string objects mostly, unnecessary object creation, creating short lived objects compared to long lived etc. The other part right sizing jvm generational partitions, using right gc algo etc. Next part would be to find out the code path with lowest latency requirement and making it hot/jitting. Even next part would be to tune OS for things like thread pinning etc etc. You can go further and tune the network layer. Every little thing counts. You can go even further and employ what's called mechanical sympathy (https://mechanical-sympathy.blogspot.com/ https://mechanical-sympathy.blogspot.com/) and write your code in a way that makes it easier for the processor to process faster. I've never worked with application that use off-heap allocations or no-gc requirements.