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
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: [email protected]
For additional commands, e-mail: [email protected]
