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There are database systems written in Java and they have no problems competing in performance with database systems written in C++. Sure, there is probably more

There are database systems written in Java and they have no problems competing in performance with database systems written in C++. Sure, there is probably more effort required with getting memory management right in case you're using Java (pooling / using off-heap memory), but Java has some other strengths, like superior concurrency support. IMHO, managed memory for system-level code is nowhere near being a "disaster". It might be sometimes tricky to get right, but not any harder than getting manual memory management right in C++ (and smart_pointers aren't a silver bullet, neither). Additionally, there are some Java extensions that let you write real-time code in it and guarantee GC won't kick in when you don't want it to.

pandaman 13y ago
This, of course, depends on your definition of "compete" and "system-level" (e.g. I have no problem competing with professional athletes too, I just have a very serious problem winning against them but the competition is no problem at all). I write code that I consider system level (it talks to the hardware directly) and "tricky" is quite an understatement. Starting from the fact that there are half a dozen types of memory (not even talking about memory-mapped I/O) and just one "heap" in Java. Not to mention the hardware is not aware about the awesomeness of JVM and is trying to read/write actual memory pointers. I can imagine that you could get around this (as well as the lack of bit-fields and unsigned types) through some kind of memory-mapped-as-a-file trick but at this point you are not using the memory management at all. And IMHO this is very far from being "not any harder" than using pointers in C++.
- pkolaczk 13y ago
  When directly talking to hardware, C is enough. Noone is saying Java is fine doing low level stuff like device drivers (IMHO wrong tool for the job, and C++ is wrong, too). I was refering to database systems or other software that is very close to system, e.g. application- or web-servers. In this area Java is excellent choice and performance-wise it often beats C++ because of superior concurrency support. And you can always code the low-level pieces in C, if you really need those unsigned arithmetic or bitfields.
  - pandaman 13y ago
    Nobody is talking about C's insufficiency for programming. When doing anything C is enough just like any other Turing-complete language. You'd been saying that in your humble opinion system programming in Java is no harder than in C++, which is something very alien to my experience of actually programming on the system level (as same as your performance claims but I am not even going to get into this one. Last time I did a Java programmer told me that a Java program that is measuring as 4 times slower is running "on the same level", whatever that means).
    - pkolaczk 13y ago
      Is Netty system-level enough? Or Cassandra? Or Tomcat? Or Apache Spark? Or Hadoop? Or Akka? For some reasons devs chose Java to implement them, not C++. As of performance, they are doing extremely well. Last time I checked Netty vs Nginx was a tie; Tomcat vs Apache HTTP were also extremely close; Apache Spark (pure Java) is generally much faster than Impala (using C++); and Cassandra has no direct competitors written in C++ so far (not counting 1000 toy databases here), but it is definitely one of the top performant NoSQL stores out there.
      - pandaman 13y ago
        Sorry, I don't know what any of these does. When I went to school it was common convention that system level is the OS kernel, drivers and anything else that talks to the hardware.
        pjmlp 13y ago
        While I do agree with you, how do you implement such features in fully pure ISO/ANSI C++ compliant compiler?
        pandaman 13y ago
        All the hardware interface is through shared/mapped memory nowadays (there are CPUs with a dedicated I/O bus or fancy coprocessor interfaces too but even there the bulk of work is creating control structures in memory and then kicking them through a port or a coprocessor instruction). C/C++ are perfect for the memory manipulation even in their purest standard form. I imagine your concern is about deriving the addresses for register apertures or emitting specific opcodes? For the concrete addresses you just link with the symbols defined outside of your C code. Special ops cannot be done in pure standard, but this is not an issue in practice as there are no pure standard compilers. Even for app development you want intrinsics just for the vector, cache and bit instructions.

pandaman 13y ago

This, of course, depends on your definition of "compete" and "system-level" (e.g. I have no problem competing with professional athletes too, I just have a very serious problem winning against them but the competition is no problem at all). I write code that I consider system level (it talks to the hardware directly) and "tricky" is quite an understatement. Starting from the fact that there are half a dozen types of memory (not even talking about memory-mapped I/O) and just one "heap" in Java. Not to mention the hardware is not aware about the awesomeness of JVM and is trying to read/write actual memory pointers. I can imagine that you could get around this (as well as the lack of bit-fields and unsigned types) through some kind of memory-mapped-as-a-file trick but at this point you are not using the memory management at all. And IMHO this is very far from being "not any harder" than using pointers in C++.

pkolaczk 13y ago
When directly talking to hardware, C is enough. Noone is saying Java is fine doing low level stuff like device drivers (IMHO wrong tool for the job, and C++ is wrong, too). I was refering to database systems or other software that is very close to system, e.g. application- or web-servers. In this area Java is excellent choice and performance-wise it often beats C++ because of superior concurrency support. And you can always code the low-level pieces in C, if you really need those unsigned arithmetic or bitfields.
- pandaman 13y ago
  Nobody is talking about C's insufficiency for programming. When doing anything C is enough just like any other Turing-complete language. You'd been saying that in your humble opinion system programming in Java is no harder than in C++, which is something very alien to my experience of actually programming on the system level (as same as your performance claims but I am not even going to get into this one. Last time I did a Java programmer told me that a Java program that is measuring as 4 times slower is running "on the same level", whatever that means).
  - pkolaczk 13y ago
    Is Netty system-level enough? Or Cassandra? Or Tomcat? Or Apache Spark? Or Hadoop? Or Akka? For some reasons devs chose Java to implement them, not C++. As of performance, they are doing extremely well. Last time I checked Netty vs Nginx was a tie; Tomcat vs Apache HTTP were also extremely close; Apache Spark (pure Java) is generally much faster than Impala (using C++); and Cassandra has no direct competitors written in C++ so far (not counting 1000 toy databases here), but it is definitely one of the top performant NoSQL stores out there.
    - pandaman 13y ago
      Sorry, I don't know what any of these does. When I went to school it was common convention that system level is the OS kernel, drivers and anything else that talks to the hardware.
      - pjmlp 13y ago
        While I do agree with you, how do you implement such features in fully pure ISO/ANSI C++ compliant compiler?
        pandaman 13y ago
        All the hardware interface is through shared/mapped memory nowadays (there are CPUs with a dedicated I/O bus or fancy coprocessor interfaces too but even there the bulk of work is creating control structures in memory and then kicking them through a port or a coprocessor instruction). C/C++ are perfect for the memory manipulation even in their purest standard form. I imagine your concern is about deriving the addresses for register apertures or emitting specific opcodes? For the concrete addresses you just link with the symbols defined outside of your C code. Special ops cannot be done in pure standard, but this is not an issue in practice as there are no pure standard compilers. Even for app development you want intrinsics just for the vector, cache and bit instructions.