On Mon, 22 Feb 2021 21:31:21 GMT, Xue-Lei Andrew Fan <xue...@openjdk.org> wrote:
>> Actually there's a much easier solution to reduce the number of slow >> `put()`s without making any behavioral changes. >> The cache object could store the earliest expire time, and then exit >> `expungeExpiredEntries()` early when current time is earlier than the >> earliest expire time - when it is, we know that there are no expired items >> in the queue and we can skip the scan entirely. >> @XueleiFan do you think the above is worth exploring? > >> Actually there's a much easier solution to reduce the number of slow >> `put()`s without making any behavioral changes. >> The cache object could store the earliest expire time, and then exit >> `expungeExpiredEntries()` early when current time is earlier than the >> earliest expire time - when it is, we know that there are no expired items >> in the queue and we can skip the scan entirely. >> @XueleiFan do you think the above is worth exploring? > > Definitely, I think it is a good improvement. Actually, it is a surprise to > me that the current code is not working this way. > > Sorry, I was/am on vacation, and the review could be delayed for a few days. I reverted all earlier Cache changes, and added a new commit that caches the earliest expire time of all cached items. The observable behavior of the new code is identical to original - items are removed from cache at exactly the same time as before; we only skip scanning the cache when we know that there are no expired items inside. The performance is substantially improved. There can be at most `cache size` scans in every `cache lifetime` period, which is roughly one scan every 4 seconds with the default SSL session cache settings. This is much better than possibly scanning on every `put()` that was possible before the changes. My reduced set of benchmarks produced the following values: Benchmark (size) (timeout) Mode Cnt Score Error Units CacheBench.put 20480 86400 avgt 25 148.345 ? 1.970 ns/op CacheBench.put 20480 0 avgt 25 108.598 ? 3.787 ns/op CacheBench.put 204800 86400 avgt 25 151.318 ? 1.872 ns/op CacheBench.put 204800 0 avgt 25 106.650 ? 1.080 ns/op which is comparable to what was observed with the previous commits. ------------- PR: https://git.openjdk.java.net/jdk/pull/2255
