3 ms·

I'm excited to try Java9. I have an app that holds alot of strings in memory. I'm curious/hoping the 'compact strings' feature makes a noticeable difference o

I'm excited to try Java9. I have an app that holds alot of strings in memory. I'm curious/hoping the 'compact strings' feature makes a noticeable difference on memory usage.

shock 9y ago
If you have many strings that are the same you can use String interning[0] to reduce the memory usage. 0 - http://java-performance.info/string-intern-in-java-6-7-8/ http://java-performance.info/string-intern-in-java-6-7-8/
- nalllar 9y ago
  You will probably see better performance if you write your own string deduplication. https://shipilev.net/jvm-anatomy-park/10-string-intern/ https://shipilev.net/jvm-anatomy-park/10-string-intern/ > In almost every project we were taking care of, removing String.intern() from the hotpaths, or optionally replacing it with a handrolled deduplicator, was the very profitable performance optimization. Do not use String.intern() without thinking very hard about it, okay?
- stevehiehn 9y ago
  That's not going to help my current situation, but either way, thanks, that's really good to know.
- hyperpape 9y ago
  They're really different issues. Deduplication reduces the memory consumption of duplicate strings. Compact strings reduce the memory consumption of ascii strings, regardless of whether they're unique or mostly duplicates. So depending on your situation, you could want either, both, or neither. There is some overlap, however. If you have a lot of ascii strings but also a high level of duplication, either approach will save some memory, but if deduplication by itself saves x bytes, and compact strings saves y, using both will save a lot less than x + y bytes. And, like the later poster says, don't use String.intern() for deduplication.
  - shock 9y ago
    > They're really different issues. They're different fixes for the same problem: high memory usage. Depending on the situation you can use one or both, as you say.
zipperhead 9y ago
Isn't this already in java 8? As of update 20 you can set -XX:+UseStringDeduplication if you are using the new -XX:+UseG1GC garbage collector.

I'm excited to try Java9. I have an app that holds alot of strings in memory. I'm curious/hoping the 'compact strings' feature makes a noticeable difference on memory usage.

shock 9y ago

If you have many strings that are the same you can use String interning[0] to reduce the memory usage. 0 - http://java-performance.info/string-intern-in-java-6-7-8/ http://java-performance.info/string-intern-in-java-6-7-8/

nalllar 9y ago
You will probably see better performance if you write your own string deduplication. https://shipilev.net/jvm-anatomy-park/10-string-intern/ https://shipilev.net/jvm-anatomy-park/10-string-intern/ > In almost every project we were taking care of, removing String.intern() from the hotpaths, or optionally replacing it with a handrolled deduplicator, was the very profitable performance optimization. Do not use String.intern() without thinking very hard about it, okay?
stevehiehn 9y ago
That's not going to help my current situation, but either way, thanks, that's really good to know.
hyperpape 9y ago
They're really different issues. Deduplication reduces the memory consumption of duplicate strings. Compact strings reduce the memory consumption of ascii strings, regardless of whether they're unique or mostly duplicates. So depending on your situation, you could want either, both, or neither. There is some overlap, however. If you have a lot of ascii strings but also a high level of duplication, either approach will save some memory, but if deduplication by itself saves x bytes, and compact strings saves y, using both will save a lot less than x + y bytes. And, like the later poster says, don't use String.intern() for deduplication.
- shock 9y ago
  > They're really different issues. They're different fixes for the same problem: high memory usage. Depending on the situation you can use one or both, as you say.

zipperhead 9y ago

Isn't this already in java 8? As of update 20 you can set -XX:+UseStringDeduplication if you are using the new -XX:+UseG1GC garbage collector.