Recommended Heap - Documentation Error?

[clintongormley]

From @Rylon on October 22, 2015 15:13

Hi,

Just a quick one, I was reviewing the notes on recommended maximum heap sizes, but noticed one document states 32GB where another states 30.5GB. I assume it's 30.5GB since that is the latest recommendation from Oracle?

https://www.elastic.co/guide/en/elasticsearch/guide/current/heap-sizing.html
https://www.elastic.co/guide/en/elasticsearch/guide/current/_limiting_memory_usage.html

Thanks!

Copied from original issue: elastic/elasticsearch#14254

[polyfractal]

Making a note for myself: this is partially fixed via #455, but the "Limiting Memory Usage" section needs a more heavy-handed treatment because of the changeover to doc values (e.g. spend more time talking about doc values and their impact on heap sizing, little on mitigating field data heap usage).

[salekseev]

Does it make sense to add an explanation of benefits to using Zero based Compressed Oops vs Regular?

$ java -XX:+UseCompressedOops -XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode -Xmx31g -version 2>&1 | grep "Compressed Oops"
heap address: 0x00007fa145000000, size: 31744 MB, Compressed Oops with base: 0x00007fa144fff000
$ java -XX:+UseCompressedOops -XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode -Xmx30g -version 2>&1 | grep "Compressed Oops"
heap address: 0x0000000080000000, size: 30720 MB, zero based Compressed Oops