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https://issues.apache.org/jira/browse/COLLECTIONS-413?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Adrian Nistor updated COLLECTIONS-413:
--------------------------------------
Description:
Hi,
I am encountering a performance problem in DualHashBidiMap. It
appears in version 3.2.1 and also in revision 1352574 (21 June 2012).
I attached a test that exposes this problem and a patch that fixes it.
On my machine, for this test, the patch provides a 173X speedup.
To run the test, just do:
$ java Test
The output for the un-patched version is:
Time is 5029
The output for the patched version is:
Time is 29
The attached test shows that, for a "DualHashBidiMap bidi" object, the
following operation is very slow:
bidi.entrySet().removeAll(toRemove);
DualHashBidiMap.entrySet() returns a
"DualHashBidiMap.EntrySet" object, which inherits
removeAll(Collection<?> coll) from "DualHashBidiMap.View".
As the patch shows, the problem is that
"DualHashBidiMap.View.removeAll(Collection<?> coll)" performs
"coll.contains(it.next())" for each element in the View.
"coll.contains(it.next())" can be very slow, e.g., if "coll" is a
list.
The patch avoids this cost by using remove(Object obj) (defined in
"EntrySet<K, V>", "KeySet<K>", and "Values<V>"), which is fast because
it uses only operations on sets.
Is this a bug, or am I misunderstanding something? If so, can you
please confirm that the patch is correct?
Thanks,
Adrian
was:
Hi,
I am encountering a performance problem in DualHashBidiMap. It
appears in version 3.2.1 and also in revision 1352574 (21 June 2012).
I attached a test that exposes this problem and a patch that fixes it.
On my machine, for this test, the patch provides a 173X speedup.
To run the test, just do:
$ java Test
The output for the un-patched version is:
Time is 5029
The output for the patched version is:
Time is 29
The attached test shows that, for a "DualHashBidiMap bidi" object, the
following operation is very slow:
bidi.entrySet().removeAll(toRemove);
DualHashBidiMap.entrySet() returns a
"DualHashBidiMap.EntrySet" object, which inherits
removeAll(Collection<?> coll) from "DualHashBidiMap.View".
As the patch shows, the problem is that
"DualHashBidiMap.View.removeAll(Collection<?> coll)" performs
"coll.contains(it.next())" for each element in the View.
"coll.contains(it.next())" can be very slow, e.g., if "coll" is a
list.
The patch avoids this cost by removing from decorate(), which is fast
because decorate() is a set.
Is this a bug, or am I misunderstanding something? If so, can you
please confirm that the patch is correct?
Thanks,
Adrian
> Performance problem in DualHashBidiMap
> --------------------------------------
>
> Key: COLLECTIONS-413
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-413
> Project: Commons Collections
> Issue Type: Bug
> Affects Versions: 3.2.1
> Environment: java 1.6.0_24
> Ubuntu 11.10
> Reporter: Adrian Nistor
> Attachments: Test.java, removeAll.diff
>
>
> Hi,
> I am encountering a performance problem in DualHashBidiMap. It
> appears in version 3.2.1 and also in revision 1352574 (21 June 2012).
> I attached a test that exposes this problem and a patch that fixes it.
> On my machine, for this test, the patch provides a 173X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 5029
> The output for the patched version is:
> Time is 29
> The attached test shows that, for a "DualHashBidiMap bidi" object, the
> following operation is very slow:
> bidi.entrySet().removeAll(toRemove);
> DualHashBidiMap.entrySet() returns a
> "DualHashBidiMap.EntrySet" object, which inherits
> removeAll(Collection<?> coll) from "DualHashBidiMap.View".
> As the patch shows, the problem is that
> "DualHashBidiMap.View.removeAll(Collection<?> coll)" performs
> "coll.contains(it.next())" for each element in the View.
> "coll.contains(it.next())" can be very slow, e.g., if "coll" is a
> list.
> The patch avoids this cost by using remove(Object obj) (defined in
> "EntrySet<K, V>", "KeySet<K>", and "Values<V>"), which is fast because
> it uses only operations on sets.
> Is this a bug, or am I misunderstanding something? If so, can you
> please confirm that the patch is correct?
> Thanks,
> Adrian
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