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From Martin Kočí (Commented) (JIRA) <>
Subject [jira] [Commented] (MYFACES-3435) [perf] _DeltaList: use ArrayList as parent
Date Thu, 26 Jan 2012 16:34:38 GMT


Martin Kočí commented on MYFACES-3435:

> because we can't assume the parent is implemented in some specific way ...
I don't understand that fully: current code uses delegation pattern with ArrayList : it already
assumes, that ArrayList implements methods in fashion we need. But I agree, that delegation
pattern is elegant, but inheritance is sometimes worth too.

Ad performance improvement: small if views are small and concurrency low. But consider this

a view with 500 component + 500 concurrent request:
500 component=
with for example 200 leafs = 300 ComponentChildrenList instances + 300 ArrayList instances
200 leafs (for example UIInput with a validator): 200 _DeltaList instances + 200 ArrayList
= 1000 instances

1000 x 500 concurrent request = 500 000 instances, very short lived, normally under 500 ms.
Those instances come only from VLD.buildView "pseudo" phase and represent very short lived
memory representation of components tree (other part of code like state saving produce other
amount of short lived instances)

Garbage collector must for each instance compute if it is GCable or not (or something like
that) : it takes very small time in modern JVM but this time is noticeable if the amout of
object is enormous. 

Then, if user will perform a simple ajax request/response in such view with 500 components
<h:inputText value="#{someBean}" >
<f:ajax render="@this" execute="@this" />

takes the garbage collecting more time that the render response phase. Yes, it depends on
GC algorithm and normally does not block the http request/response thread. I tested it on
HotSpot from JVM 6.0.30 with all server-side suitable GCs and with JRockit 4.1 Generational
Parallel Mark & Sweep. 

But this issue is clearly not very important right now: the performace gain is not so big
 as in other improvement which I'm going to propose (as String's id caching in ComponentTagHandler
or isRenderedSet() method)
> [perf] _DeltaList: use ArrayList as parent
> ------------------------------------------
>                 Key: MYFACES-3435
>                 URL:
>             Project: MyFaces Core
>          Issue Type: Improvement
>          Components: General
>    Affects Versions: 2.0.12-SNAPSHOT, 2.1.6-SNAPSHOT
>            Reporter: Martin Kočí
>            Assignee: Martin Kočí
>            Priority: Minor
>         Attachments: MYFACES-3435.patch,
> Two internal classes _DeltaList in API:
> 1) now use delegation pattern, but are always initialized with an ArrayList instance
-> use inheritance and  ArrayList as parent -> improvement in memory area, reduces number
of GCed object in one request/response of (_DeltaList instances/2) 
> 2) initialize expected size of _DeltaList (for example, number of validators per one
component is perhaps never 10, use: new _DeltaList(5))
> 3) use indexes in 'for' instead of iterator (java.util.RandomAccess) ->  improvement
in performance

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