[Engine-devel] Guid improvements

Sun Jun 30 10:08:20 UTC 2013

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. 

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