Re: [Engine-devel] Guid improvements

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(a)redhat.com <mailto:mpastern@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(a)redhat.com <mailto:amureini@redhat.com>> >>>>>>> To: "engine-devel" <engine-devel(a)ovirt.org <mailto:engine-devel@ovirt.org>>, "Barak Azulay" <bazulay(a)redhat.com <mailto:bazulay@redhat.com>> >>>>>>> Cc: "Yair Zaslavsky" <yzaslavs(a)redhat.com <mailto:yzaslavs@redhat.com>>, "Michael Pasternak" <mpastern(a)redhat.com <mailto:mpastern@redhat.com>>, "Tal Nisan" >>>>>>> <tnisan(a)redhat.com <mailto:tnisan@redhat.com>>, "Ayal Baron" <abaron(a)redhat.com <mailto:abaron@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... >>>>>>> >>>>>> _______________________________________________ >>>>>> Engine-devel mailing list >>>>>> Engine-devel(a)ovirt.org <mailto:Engine-devel@ovirt.org> >>>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel >>>>> >>>>> _______________________________________________ >>>>> Engine-devel mailing list >>>>> Engine-devel(a)ovirt.org <mailto:Engine-devel@ovirt.org> >>>>> http://lists.ovirt.org/mailman/listinfo/engine-devel >>>>> >>>> >>>> >>>> -- >>>> >>>> Michael Pasternak >>>> RedHat, ENG-Virtualization R&D >>> >> >> >> -- >> >> Michael Pasternak >> RedHat, ENG-Virtualization R&D >> >> > > > -- > > Michael Pasternak > RedHat, ENG-Virtualization R&D