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From Robert Zeigler <robert.zeig...@roxanemy.com>
Subject Re: Cayenne object storage / memory usage
Date Thu, 06 Jul 2017 12:31:56 GMT
Kudos on the improvements, and to the original developers (Andrus, et al) for a fantastic design.
These days, I’ve been doing a lot more Python coding than Java and I use SQLAlchemy pretty
extensively. It’s nice… but I still miss Cayenne’s simplicity/ease of use (SQLAlchemy
uses a transaction model more akin to Hibernate, though not as egregious).

Best,

Robert

> On Jul 6, 2017, at 7:27 AM, Andrus Adamchik <andrus@objectstyle.org> wrote:
> 
> The fact that we can switch to field-based DataObjects with minimal effort and without
sacrificing a single thing in the Cayenne design is a *very* big deal! Thanks John for bringing
the possibility to everyone's attention, and Nikita - for the working code and benchmarks.

> 
> I am going to try this out on a real app some time next week. Very exciting! :)
> 
> Andrus
> 
> 
>> On Jul 5, 2017, at 5:19 PM, Nikita Timofeev <ntimofeev@objectstyle.com> wrote:
>> 
>> Hi all,
>> 
>> I've run some additional benchmarks for field-based classes inspired
>> by John and they were so promising, that I've moved on
>> to the implementation.
>> 
>> So here is pull request for you to review [1].
>> Here [2] you can see what new generated classes will look like.
>> 
>> For me there is no visible downsides in this solution, e.g. both
>> memory usage and speed are improved.
>> All tests are clean and the only minor incompatibility out there
>> is in HOLLOW state that no longer resets object's values [3]
>> (though this can be implemented as well, I'm just
>> not sure this is really needed).
>> 
>> P.S. here is some raw numbers from my benchmarks.
>> I'm giving absolute numbers, but really only their relation is important.
>> Results for old version are on the left, for new version on the right.
>> 
>> Memory usage:
>> ==============
>> 1. 10.000 small objects
>> (int, Date and String ~ 20 chars)
>>>>> 6Mb vs 2.5Mb <<<
>> 
>> 2. 10.000 objects with big values
>> (int, Date and String ~ 1K chars)
>> Actually in case of same classes (same field number),
>> there will be just constant difference,
>> so this is just to get idea what to expect in different cases.
>>>>> 24.5Mb vs 21Mb <<<
>> 
>> Performance:
>> ==============
>> (numbers are in millions ops per sec, measured with JMH benchmark)
>> 1. Getter:
>>>>> 107 vs 177 <<<
>> 
>> 2. Setter:
>> Not so impressive, as Cayenne stack took most of the
>> time here to process graph diff, but still new methods are better.
>>>>> 12.5 vs 14.5 <<<
>> 
>> 3. readPropertyDirectly:
>>>>> 152 vs 248 <<<
>> 
>> 4. writePropertyDirectly:
>> This is map.put() vs switch(String) battle,
>> and map definitely loosing it :)
>>>>> 126 vs 582 <<<
>> 
>> [1] https://github.com/apache/cayenne/pull/235
>> [2] https://github.com/stariy95/cayenne/blob/544aae0866e8fb1712f07f00794ea3263a4c95b5/cayenne-server/src/test/java/org/apache/cayenne/testdo/testmap/auto/_Artist.java
>> [3] https://github.com/stariy95/cayenne/blob/544aae0866e8fb1712f07f00794ea3263a4c95b5/cayenne-server/src/test/java/org/apache/cayenne/access/DataContextExtrasIT.java#L144
>> 
>> On Wed, Jun 21, 2017 at 10:20 PM, John Huss <johnthuss@gmail.com> wrote:
>>> I was surprised by the difference in memory too, but this is a small diff
>>> (apart from the newly generated readPropertyDirectly/writePropertyDirectly
>>> methods) so there isn't anything else going on.  My unverified assumption
>>> of HashMap is that is doubles in size each time it resizes, so entities
>>> with more fields could cause more waste. For example a entity with 65
>>> fields would have 63 empty array slots (ignoring fill factor).  So the
>>> exact savings may vary.
>>> 
>>> On Sat, Jun 17, 2017 at 1:01 AM Robert Zeigler <robert.zeigler@roxanemy.com>
>>> wrote:
>>> 
>>>> I’m also a little surprised at the 1/2-ing… what were the values being
>>>> stored? I suppose in theory, many values are relatively “small”,
>>>> memory-wise, so having the overhead of also storing the key could ~double
>>>> the memory use, but if you’re storing large values, I wouldn’t expect
the
>>>> utilization to drop as dramatically. What were your data values (type and
>>>> length distribution for strings)?
>>>> 
>>>> Thanks!
>>>> 
>>>> Robert
>>>> 
>>>>> On Jun 10, 2017, at 6:49 AM, Michael Gentry <blacknext@gmail.com>
wrote:
>>>>> 
>>>>> Hi John,
>>>>> 
>>>>> I'm a little surprised that map-based storage is over 2x worse in memory
>>>>> consumption.  I'm wondering if there is more going on here than storage
>>>> of
>>>>> the property values.  Would it be simple enough to adapt your test case
>>>> to
>>>>> compare a list of POJOs vs a list of maps and see what the memory
>>>> footprint
>>>>> and difference is that way?
>>>>> 
>>>>> I personally was thinking the big improvement for using fields directly
>>>> is
>>>>> the speed improvement.  I didn't think the memory consumption difference
>>>>> would be that dramatic.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> mrg
>>>>> 
>>>>> 
>>>>> On Fri, Jun 9, 2017 at 10:55 AM, John Huss <johnthuss@gmail.com>
wrote:
>>>>> 
>>>>>> I did some experimenting recently to see if changes to the way data
in
>>>>>> stored in Cayenne objects could reduce the amount of memory they
>>>> consume.
>>>>>> 
>>>>>> I chose to use separate fields for each property instead of a HashMap
>>>>>> (which is what CayenneDataObject uses).  The results were very
>>>> affirming.
>>>>>> For my test of loading 10,000 objects from every table in my database
I
>>>> got
>>>>>> it to use about about *half the memory* of the default class (from
921
>>>> MB
>>>>>> down to 431 MB).
>>>>>> 
>>>>>> I know there has been some discussion already about addressing this
>>>> topic
>>>>>> for the next major release, so I thought I'd throw in some observations
>>>> /
>>>>>> questions here.
>>>>>> 
>>>>>> For my implementation I subclassed CayenneDataObject because in previous
>>>>>> experience I found implementing a replacement to be much more difficult
>>>> and
>>>>>> subject to more bugs due to the less frequently used code path that
>>>>>> PersistentObject and it's descriptors take you down.  My apps rely
on
>>>>>> things that are sort of specific to CayenneDataObject like Validating.
>>>>>> 
>>>>>> So one question is how we should be addressing the need that people
may
>>>>>> have to create their own data classes. Right now I believe the
>>>> recommended
>>>>>> path is to subclass PersistentObject, but I'm not convinced that
that
>>>> is a
>>>>>> viable solution without wholesale copying most of CayenneDataObject
into
>>>>>> your subclass.  I'd rather see a fuller base class (in addition to
>>>> keeping
>>>>>> PersistentObject around) that includes all of CayenneDataObject except
>>>> the
>>>>>> property storage (HashMap).
>>>>>> 
>>>>>> For my implementation I had to modify CayenneDataObject, but only
>>>> slightly
>>>>>> to avoid creating the HashMap which I wasn't using. However, because
>>>> class
>>>>>> isn't really intended for customization this map is referenced in
>>>> multiple
>>>>>> methods that can't easily be overridden to change the way things
are
>>>>>> stored.
>>>>>> 
>>>>>> Another approach might be to ask why anyone should need to customize
the
>>>>>> way data is stored in the objects if we can just use the best solution
>>>>>> possible in the first place?  I can't imagine a more efficient
>>>>>> representation that fields.  However, fields present difficulties
for
>>>> the
>>>>>> use case where you aren't generating unique classes for your model
but
>>>> just
>>>>>> rely on the generic class.  In theory this could be addressed via
>>>> runtime
>>>>>> code generation or something else, but that would be quite a change.
>>>>>> 
>>>>>> So I'm looking forward to discussing this and toward the future.
>>>>>> 
>>>>>> John
>>>>>> 
>>>> 
>>>> 
>> 
>> 
>> 
>> -- 
>> Best regards,
>> Nikita Timofeev
> 


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