What is -XX:+UseCompressedOops in 64 bit JVM

What is -XX:+UseCompressedOops in 64 bit JVM

Why should you use -XX:+UseCompressedOops JVM option -XX:+UseCompressedOops JVM option neutralize penalty imposed by 64 bit JVM. By using -XX:+UseCompressedOops you can avail benefit of both 64 bit JVM in terms of larger Java heap size and 32 bit JVM in terms of compressed size of OOPS which results in better performance by utilizing CPU cache better than larger, space inefficient 64 bit OOPS pointers. Since better application performance is directly proportional to better CPU cache utilization, -XX:+UseCompressedOops allows you to get most of your available CPU registers along with additional CPU registers provided by some platforms like AMD x64. Some people may argue that further expansion of 32 bit compressed OOPS into 64 bit pointers may slow down things but that shouldn't be problem with modern high end processors.

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