You are viewing a plain text version of this content. The canonical link for it is here.
Posted to dev@lucene.apache.org by "Uwe Schindler (Issue Comment Edited) (JIRA)" <ji...@apache.org> on 2012/03/14 14:48:38 UTC
[jira] [Issue Comment Edited] (LUCENE-3867)
RamUsageEstimator.NUM_BYTES_ARRAY_HEADER is incorrect
[ https://issues.apache.org/jira/browse/LUCENE-3867?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13229191#comment-13229191 ]
Uwe Schindler edited comment on LUCENE-3867 at 3/14/12 1:47 PM:
----------------------------------------------------------------
Hm, for me (1.6.0_31, 7u3) it prints true. What JVMs are you using and what settings?
was (Author: thetaphi):
Hm, for it prints true. What JVMs are you using and what settings?
> RamUsageEstimator.NUM_BYTES_ARRAY_HEADER is incorrect
> -----------------------------------------------------
>
> Key: LUCENE-3867
> URL: https://issues.apache.org/jira/browse/LUCENE-3867
> Project: Lucene - Java
> Issue Type: Bug
> Components: core/index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Priority: Trivial
> Fix For: 3.6, 4.0
>
> Attachments: LUCENE-3867-compressedOops.patch, LUCENE-3867.patch
>
>
> RamUsageEstimator.NUM_BYTES_ARRAY_HEADER is computed like that: NUM_BYTES_OBJECT_HEADER + NUM_BYTES_INT + NUM_BYTES_OBJECT_REF. The NUM_BYTES_OBJECT_REF part should not be included, at least not according to this page: http://www.javamex.com/tutorials/memory/array_memory_usage.shtml
> {quote}
> A single-dimension array is a single object. As expected, the array has the usual object header. However, this object head is 12 bytes to accommodate a four-byte array length. Then comes the actual array data which, as you might expect, consists of the number of elements multiplied by the number of bytes required for one element, depending on its type. The memory usage for one element is 4 bytes for an object reference ...
> {quote}
> While on it, I wrote a sizeOf(String) impl, and I wonder how do people feel about including such helper methods in RUE, as static, stateless, methods? It's not perfect, there's some room for improvement I'm sure, here it is:
> {code}
> /**
> * Computes the approximate size of a String object. Note that if this object
> * is also referenced by another object, you should add
> * {@link RamUsageEstimator#NUM_BYTES_OBJECT_REF} to the result of this
> * method.
> */
> public static int sizeOf(String str) {
> return 2 * str.length() + 6 // chars + additional safeness for arrays alignment
> + 3 * RamUsageEstimator.NUM_BYTES_INT // String maintains 3 integers
> + RamUsageEstimator.NUM_BYTES_ARRAY_HEADER // char[] array
> + RamUsageEstimator.NUM_BYTES_OBJECT_HEADER; // String object
> }
> {code}
> If people are not against it, I'd like to also add sizeOf(int[] / byte[] / long[] / double[] ... and String[]).
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: dev-help@lucene.apache.org