Hi,

We have a server application that, after some longer usage, becomes  
very slow. It turned out that this is because lots of symbols are  
created from strings (without holding onto them), which becomes slower  
and slower over time. This is easy to fix in our app, but I'd like to  
understand why Squeak has a problem with that.

Using the following snipped, I produced the attached chart (Y axis is  
ms spent to create 5000 random symbols). You can nicely see the  
reoccurring pattern that grows over time.

1000 timesRepeat: [
	Transcript print: ([
		5000 timesRepeat: [ (($a to: $x) atRandom asString , 'asdasd')  
asSymbol ] ] timeToRun); cr; flush. ]

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Message tally sais:

96.2% {13872ms} ByteString(String)>>asSymbol
   |96.2% {13872ms} Symbol class>>intern:
   |  49.7% {7167ms} Symbol class>>lookup:
   |    |49.7% {7167ms} WeakSet>>like:
   |    |  49.7% {7167ms} WeakSet>>scanFor:
   |    |    32.3% {4658ms} primitives
   |    |    17.3% {2495ms} UndefinedObject(Object)>>=
   |  44.4% {6402ms} WeakSet>>add:
   |    |44.3% {6388ms} WeakSet(Set)>>findElementOrNil:
   |    |  44.3% {6388ms} WeakSet>>scanFor:
   |    |    22.8% {3288ms} UndefinedObject(Object)>>=
   |    |    21.5% {3100ms} primitives
   |  2.1% {303ms} ByteSymbol>>string:
2.9% {418ms} Character>>to:
   2.4% {346ms} SmallInteger(Number)>>to:
     2.4% {346ms} Interval class>>from:to:by:
       2.4% {346ms} Interval>>setFrom:to:by:

I haven't had time to look into this very closely yet but maybe  
somebody else already knows what is going on. My guess is that the  
NewSymbols weak set is repeatedly grown since tally is not decreased  
if the GC removes a weak element.

This is a Squeak 3.9 image (OS X and Linux).

Cheers,
Adrian

___________________
http://www.adrian-lienhard.ch/