Update tuning.md http://stackoverflow.com/questions/9699071/what-is-the-javas-internal-represention-for-string-modified-utf-8-utf-16
Author: Andrew Ash <and...@andrewash.com> Closes #384 from ash211/patch-2 and squashes the following commits: da1b0be [Andrew Ash] Update tuning.md Project: http://git-wip-us.apache.org/repos/asf/spark/repo Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/4c9906d8 Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/4c9906d8 Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/4c9906d8 Branch: refs/heads/branch-1.0 Commit: 4c9906d85b60f34e5bc0e23409a848746fe5cf96 Parents: 1e2cdbc Author: Andrew Ash <and...@andrewash.com> Authored: Thu Apr 10 14:59:58 2014 -0700 Committer: Patrick Wendell <pwend...@gmail.com> Committed: Thu Apr 10 15:11:03 2014 -0700 ---------------------------------------------------------------------- docs/tuning.md | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/spark/blob/4c9906d8/docs/tuning.md ---------------------------------------------------------------------- diff --git a/docs/tuning.md b/docs/tuning.md index 093df31..cc069f0 100644 --- a/docs/tuning.md +++ b/docs/tuning.md @@ -90,9 +90,10 @@ than the "raw" data inside their fields. This is due to several reasons: * Each distinct Java object has an "object header", which is about 16 bytes and contains information such as a pointer to its class. For an object with very little data in it (say one `Int` field), this can be bigger than the data. -* Java Strings have about 40 bytes of overhead over the raw string data (since they store it in an +* Java `String`s have about 40 bytes of overhead over the raw string data (since they store it in an array of `Char`s and keep extra data such as the length), and store each character - as *two* bytes due to Unicode. Thus a 10-character string can easily consume 60 bytes. + as *two* bytes due to `String`'s internal usage of UTF-16 encoding. Thus a 10-character string can + easily consume 60 bytes. * Common collection classes, such as `HashMap` and `LinkedList`, use linked data structures, where there is a "wrapper" object for each entry (e.g. `Map.Entry`). This object not only has a header, but also pointers (typically 8 bytes each) to the next object in the list.