RFR: 8276904: Optional.toString() is unnecessarily expensive

[Stuart Marks]

On Wed, 10 Nov 2021 17:44:04 GMT, Eamonn McManus <emcmanus at openjdk.org> wrote:

> Use string concatenation instead of `String.format`.

I talked to Brian about this a bit. Changing `format` to concatenation is probably ok this case for two reasons: 1) it's the simplest possible such transformation, and as such it's not a very good example for the templating stuff; and 2) presumably you bothered filing the bug and the PR because you believe the performance improvement would be noticeable in actual systems.

I note that some Amazon folks had filed [JDK-8275190](https://bugs.openjdk.java.net/browse/JDK-8275190) for what is essentially the same issue. (I closed it as a dupe.) They did include some performance numbers, but not the actual code they measured, so without guessing it's hard to say what they actually measured. Could you run some numbers and post them, and can you share some estimates of the impact it might have on your systems?

The reason I'm interested in some data here is that this sort of change is worth doing only if it has a real, measurable impact. In turn that implies that you're probably using `Optional::toString` a lot. That's an important criterion; we don't want to do a wholesale replacement of `format` with concatenation in the JDK, based on some micro benchmarks, that end up garbaging up the JDK code base while not actually improving any real systems.

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PR: https://git.openjdk.java.net/jdk/pull/6337