RFR: 6988220: java.lang.ObjectName use of String.intern() causes major performance issues at scale

[Eamonn McManus]

I am not sure it is worth the complexity of extra checks. Do you have data
showing that ObjectName.equals usually returns false? In a successful
HashMap lookup, for example, it will usually return true since the equals
method is used to guard against collisions, and collisions are rare by
design. Meanwhile, String.equals is intrinsic in HotSpot so we may assume
that it is highly optimized, and you are giving up that optimization if you
use other comparisons.

Éamonn


On 23 February 2012 10:52, Olivier Lagneau <olivier.lagneau at oracle.com>wrote:

> Hi Frederic,
>
> Performance and typo comments.
>
> Regarding performance of ObjectName.equals method, which is certainely
> a frequent call on ObjectNames, I think that using inner fields
> (Property array for canonical name and domain length) would be more
> efficient
> than using String.equals() on these potentially very long strings.
>
> Two differents objectNames may often have the same length with
> different key/properties values, and may often be different only
> on the last property of the canonical name.
>
> The Property array field ca_array (comparing length and property contents)
> and domain length are good candidates to filter out more efficiently
> different objectNames, knowing that String.equals will compare every
> single char of the two char arrays.
>
> So for performance purpose, I suggest to filter out different objectNames
> by doing inner comparisons in the following order : length of the two
> canonical names, then domain_length, then ca_array size, then its content,
> and lastly if all of this fails to filter out, then use String.equals.
>
>   _canonicalName = (new String(canonical_chars, 0, prop_index));
>>
> Typo : useless parentheses.
>
> Thanks,
> Olivier.
>
> -- Olivier Lagneau, olivier.lagneau at oracle.com
> Oracle, Grenoble Engineering Center - France
> Phone : +33 4 76 18 80 09 Fax : +33 4 76 18 80 23
>
>
>
>
> Frederic Parain said  on date 2/23/2012 6:01 PM:
>
>  No particular reason. But after thinking more about it,
>> equals() should be a better choice, clearer code, and
>> the length check in equals() implementation is likely
>> to help performance of ObjectName's comparisons as
>> ObjectNames are often long with a common section at the
>> beginning.
>>
>> I've updated the webrev:
>> http://cr.openjdk.java.net/~**fparain/6988220/webrev.01/<http://cr.openjdk.java.net/~fparain/6988220/webrev.01/>
>>
>> Thanks,
>>
>> Fred
>>
>> On 2/23/12 4:58 PM, Vitaly Davidovich wrote:
>>
>>> Hi Frederic,
>>>
>>> Just curious - why are you checking string equality via compareTo()
>>> instead of equals()?
>>>
>>> Thanks
>>>
>>> Sent from my phone
>>>
>>> On Feb 23, 2012 10:37 AM, "Frederic Parain" <frederic.parain at oracle.com
>>> <mailto:frederic.parain@**oracle.com <frederic.parain at oracle.com>>>
>>> wrote:
>>>
>>>    This a simple fix to solve CR 6988220:
>>>    http://bugs.sun.com/__**bugdatabase/view_bug.do?bug___**id=6988220<http://bugs.sun.com/__bugdatabase/view_bug.do?bug___id=6988220>
>>> <http://bugs.sun.com/**bugdatabase/view_bug.do?bug_**id=6988220<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6988220>
>>> >
>>>
>>>    The use of String.intern() in the ObjectName class prevents
>>>    the class the scale well when more than 20K ObjectNames are
>>>    managed. The fix simply removes the use of String.intern(),
>>>    and uses regular String instead. The Object.equals() method
>>>    is modified too to make a regular String comparison. The
>>>    complexity of this method now depends on the length of
>>>    the ObjectName's canonical name, and is not impacted any
>>>    more by the number of ObjectName instances being handled.
>>>
>>>    The Webrev:
>>>    http://cr.openjdk.java.net/~__**fparain/6988220/webrev.00/<http://cr.openjdk.java.net/~__fparain/6988220/webrev.00/>
>>> <http://cr.openjdk.java.net/~**fparain/6988220/webrev.00/<http://cr.openjdk.java.net/~fparain/6988220/webrev.00/>
>>> >
>>>
>>>    I've tested this fix with the jdk_lang and jdk_management
>>>    test suites.
>>>
>>>    Thanks,
>>>
>>>    Fred
>>>
>>>    --
>>>    Frederic Parain - Oracle
>>>    Grenoble Engineering Center - France
>>>    Phone: +33 4 76 18 81 17 <tel:%2B33%204%2076%2018%2081%**2017>
>>>    Email: Frederic.Parain at oracle.com <mailto:Frederic.Parain@**
>>> oracle.com <Frederic.Parain at oracle.com>>
>>>
>>>
>>
>