Re: Need help building an EOQualifier with session values
Re: Need help building an EOQualifier with session values
- Subject: Re: Need help building an EOQualifier with session values
- From: "Jerry W. Walker" <email@hidden>
- Date: Tue, 23 May 2006 00:56:20 -0400
Hi, Mike, et al,
Thanks for testing that, but I think there might be something wrong
with the test, and I suspect it might have something to do with
optimizing compilation.
From what you've said, your test is indicating that valueForKeyPath
takes( (992 - 935) / 1000) / 1,000,000 of a second longer per
execution than valueForKey. By my reckoning, that's 57 nanoseconds
extra each time valueForKeyPath is used rather than valueForKey.
You didn't mention what kind of processor you were running on, and
since we were doing a relative comparison, it would generally not
make a difference, but I have a hard time believing that the Java
Virtual Machine can execute a single JVM instruction in 57
nanoseconds. So we're probably dealing with a JIT compiler. That
would change the issue to executing native code. Is it possible on
your machine to execute a single instruction (approximately) in 57
nanoseconds?
I have the feeling that in the loop, the compiler has determined the
result we're trying to get is not changing, identified it as a
constant path for each of valueForKey and valueForKeyPath and is
caching something for us.
My (unsupported) feeling is that the 57 millisecond difference that
we're seeing from the million iterations, might be the difference to
obtain only the very first result for each approach, which is then
cached somehow and we're using the exact same approach (to obtain a
cached value) in both cases after the caching, so no more difference.
It's late, so I'll try to set up a slightly different test tomorrow.
Regards,
Jerry
On May 22, 2006, at 3:51 PM, Mike Schrag wrote:
Technically speaking, you can ALWAYS use valueForKeyPath and it
will work. Obviously valueForKey does not have that attribute.
So the question is performance ... I've kind of wondered this
before also. So in the spirit of knowing-is-half-the-battle:
I have an object with one method "public String getName()" and ran
one million iterations of the following:
NSKeyValueCoding.Utility.valueForKey "name": 935ms
NSKeyValueCodingAdditions.Utility.valueForKeyPath "name": 992ms
NSKeyValueCodingAdditions.Utility.valueForKeyPath "name.length":
2713ms
That's total time for all 1 million. So basically no diff using
keypath vs key -- i would say always use it. I included the next
one just because it was kind of interesting. Obviously there
aren't enough examples to know if that's a function of the
performance of .length() on String or whether traversing multiple
keypaths is nasty.
On May 22, 2006, at 3:33 PM, Zak Burke wrote:
Chuck Hill wrote on 5/21/06 11:44 AM:
NSArray bindings = new NSArray( new Object [] {
(Session)session().valueForKey("user.client.clientName") } );
valueForKeyPath not valueForKey
I've been bitten by this one too.
Is there ever a reason to use valueForKey instead of
valueForKeyPath? (I
ask this question along the same vein as, "Is the simplicity of
always
using addObjectToBothSidesOfRelationshipWithKey worth the potential
performance hit compared to addObjectToPropertyWithKey?")
The NSKeyValueCodingAdditions documentation doesn't allude to any
performance hits, and says its basically implemented in terms of
value
for key. Is valueForKey faster? I supposed it would be because it
won't
even try to access items along the keypath; it'll just die right
away.
As an aside, is it possible for an item to have a valid key
containing a
dot? Don't keys eventually map to object properties that have to
conform
to java variable names?
zak.
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--
__ Jerry W. Walker,
WebObjects Developer/Instructor for High Performance Industrial
Strength Internet Enabled Systems
email@hidden
203 278-4085 office
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