[Engine-devel] Guid improvements

Sun Jun 30 10:15:34 UTC 2013

On 06/30/2013 01:08 PM, Liran Zelkha wrote:
> Why synchronization? No need for it. Worst case scenario a put (which should be much less common then get) will occur twice on the same key. 

why assuming a best & not worst scenario? don't forget that every new insertion requires collision resolution
which is triggers .equals() on the GUID.

> 
> On Jun 30, 2013, at 1:00 PM, Michael Pasternak wrote:
> 
>> On 06/30/2013 12:45 PM, Liran Zelkha wrote:
>>> All is true. But average UUID.fromString execution is 1675us, and HashMap.put is 78us - so the benefit is clear when we're talking on >100K executions for 10minutes...
>>
>> even with synchronization? what about ConcurrentHashMap?
>>
>>>
>>>
>>> On Sun, Jun 30, 2013 at 12:44 PM, Michael Pasternak <mpastern at redhat.com <mailto:mpastern at redhat.com>> wrote:
>>>
>>>    On 06/30/2013 12:20 PM, Liran Zelkha wrote:
>>>> I checked such a solution using JProfiler. Creating the GUID object takes much more CPU cycles that checking the string in the Map.
>>>
>>>    of course it is, but what is the size of map that you checked?, check on worst scenario, i.e map
>>>    is full of all possible guids,
>>>
>>>    also problem a bit different,java map has a load factor (which is usually 0.75),
>>>    when ratio increases beyond the load factor, occurs proses called re-hash so that the hash
>>>    table will double amount of buckets. what can produce a cpu spikes (though it should not happen too often),
>>>    to avoid this the initial capacity should be greater than the maximum number of entries / the
>>>    load factor, and this is a huge map....
>>>
>>>    so basically this is a tradeoff between time and space costs against the new guid generation.
>>>
>>>>
>>>> On Jun 30, 2013, at 12:06 PM, Michael Pasternak wrote:
>>>>
>>>>> On 06/30/2013 11:37 AM, Liran Zelkha wrote:
>>>>>> Great news.
>>>>>> Allon - please note that GUID is being recreated from String by both DB calls and by data received from VDSM. It is VERY useful to cache Guid String-->Guid, and not
>>>    just Empty GUID.
>>>>>>
>>>>>> However, as the Guid class runs in GWT as well, you can't use Infinispan and you're limited in the HashMap implementations you can use.
>>>>>> Personally, I don't think it's a memory leak, as GUID number in the system are finite and not too large.
>>>>>
>>>>> it's large, it's 128-bit random number, it's not about memory leaking, but cpu cost,
>>>>> as you'll face a lot of rehash'ings in the map,
>>>>>
>>>>> i'm not even sure that using indexing in the map can help, worth checking.
>>>>>
>>>>> What do you think? Want to add it to your patch?
>>>>>
>>>>>
>>>>>>
>>>>>> On Jun 30, 2013, at 11:13 AM, Yair Zaslavsky wrote:
>>>>>>
>>>>>>> Well done, should have been done ages ago :)
>>>>>>> Now, for the painful rebase of async_task_mgr changes :)
>>>>>>>
>>>>>>>
>>>>>>> ----- Original Message -----
>>>>>>>> From: "Allon Mureinik" <amureini at redhat.com <mailto:amureini at redhat.com>>
>>>>>>>> To: "engine-devel" <engine-devel at ovirt.org <mailto:engine-devel at ovirt.org>>, "Barak Azulay" <bazulay at redhat.com <mailto:bazulay at redhat.com>>
>>>>>>>> Cc: "Yair Zaslavsky" <yzaslavs at redhat.com <mailto:yzaslavs at redhat.com>>, "Michael Pasternak" <mpastern at redhat.com <mailto:mpastern at redhat.com>>, "Tal Nisan"
>>>>>>>> <tnisan at redhat.com <mailto:tnisan at redhat.com>>, "Ayal Baron" <abaron at redhat.com <mailto:abaron at redhat.com>>
>>>>>>>> Sent: Sunday, June 30, 2013 11:11:30 AM
>>>>>>>> Subject: Guid improvements
>>>>>>>>
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> I just merged a couple of improvements to the [N]Guid class [1] to improve
>>>>>>>> it's performance both CPU-wise and memory-wise, based on a set of benchmarks
>>>>>>>> presented by Liran.
>>>>>>>>
>>>>>>>> What this patchset achieves:
>>>>>>>> 1. Clean up the code, so it's easier to understand and use
>>>>>>>> 2. Eliminate the inflation in the memory foot print caused by the getValue()
>>>>>>>> method
>>>>>>>> 3. Eliminate all the heavy calls to UUID.fromString when creating a new/empty
>>>>>>>> Guid instance as a default value
>>>>>>>> 4. Note that the cleanups proposed in (1) will have minor performance
>>>>>>>> benefits (e.g., eliminating useless conditional statements), but I doubt
>>>>>>>> this would be anything to write home about.
>>>>>>>>
>>>>>>>> From a developer's perspective, here's what changed:
>>>>>>>> 1. No more NGuid, just Guid. Both static methods to create a Guid from String
>>>>>>>> still exist, and are named createGuidFromString and
>>>>>>>> createGuidFromStringDefaultEmpty.
>>>>>>>> 2. [N]Guid.getValue() was removed, it's no longer needed after (1) was
>>>>>>>> implemented
>>>>>>>> 3. The Guid() constructor was made private, as it forced a redundant call to
>>>>>>>> UUID.fromString(String). If you need an empty Guid instance, just use
>>>>>>>> Guid.Empty
>>>>>>>> 4. The Guid.EMPTY_GUID_VALUE string constant was removed, as it was used for
>>>>>>>> redundant calls to UUID.fromString. If you really, REALLY, need it, just
>>>>>>>> call Guid.Empty.getValue() for a UUID or Guid.Empty.toString() for a String.
>>>>>>>> 5. All sorts of ways to transform Strings to Guids were removed. If you have
>>>>>>>> a literal you trust, just use new Guid(String). If you suspect it may be
>>>>>>>> null, use Guid.createGuidFromString[DefaultEmpty]
>>>>>>>> 6. NewGuid is now called newGuid. We're in Java, not C# :-)
>>>>>>>>
>>>>>>>>
>>>>>>>> Many thanks to everyone who reviewed this patchset.
>>>>>>>> You guys rock!
>>>>>>>>
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Allon
>>>>>>>>
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> http://gerrit.ovirt.org/#/q/project:ovirt-engine+branch:master+topic:guid-cleanup,n,z
>>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Michael Pasternak
>>>>> RedHat, ENG-Virtualization R&D
>>>>
>>>
>>>
>>>    --
>>>
>>>    Michael Pasternak
>>>    RedHat, ENG-Virtualization R&D
>>>
>>>
>>
>>
>> -- 
>>
>> Michael Pasternak
>> RedHat, ENG-Virtualization R&D
> 

-- 

Michael Pasternak
RedHat, ENG-Virtualization R&D