Hi, This seems to be a simple one-liner fix, but the background is more complicated. See the bug: https://bugs.openjdk.java.net/browse/JDK-8076759
The bottom line is that our current resizing policy in ASB is hostile for long appends. There is a heuristics that extends the capacity to match the *exact* length of append if doubling the array would not help. This heuristics has a nasty corner case: if there is an upcoming append after a large one, then we are guaranteed to re-size again. If an upcoming append is large in itself, the resizing is inevitable even under the doubling-the-storage strategy; but if we only do a small append, then we can be smarter. After trying a few options to fix this (see below), I have settled on just adding a simple static "pad", to absorb the trivial appends after a large append: http://cr.openjdk.java.net/~shade/8076759/webrev.00/ The choice of "32" as magic number is deliberate: arraycopy likes large power-of-two strides (and it does not like to make catch up loops for small residuals). "16" is too small to fit the decimal representation of Long.MIN_VALUE, therefore, we pick "32". There are other approaches, briefly mentioned here: http://cr.openjdk.java.net/~shade/8076759/patches.txt There is a direct correlation between the allocation pressure, and test performance: http://cr.openjdk.java.net/~shade/8076759/data-perf.png http://cr.openjdk.java.net/~shade/8076759/data-foot.png Naively, one could expect doubling the storage ("mult2") until we reach $minimalCapacity solves the problem, but it wastes too much memory, and only reaches the "plus32" on power-of-two sizes. That is also the Achilles' Heel of the heuristics, because appending the power-of-two-plus-one-sized string will set us up for the original problem. This effect can be alleviated by doing the padding as well ("mult2-plus32"). Exactly the same trouble manifests on smaller strings that go through the usual double-the-storage route, and this is why a proposed patch makes the pad on common path. I do believe the current heuristics is smart about large appends, and mult2* strategies undo it. Therefore, I would think keeping the minimumCapacity cap is a good thing, and just adding the pad is a good solution. Thus, it is in the webrev. Thanks, -Aleksey.
