Deduplicator java app5/8/2023 The Table section gives statistics about the internal tracking table, and the Queue one lists how many requests for deduplication have been dropped due to load, which is one part of the overhead reduction mechanism. In above case all strings could be deduplicated, removing 4.5MB of data from memory. These numbers look different in real apps, where strings are passed multiple times, thus some might be skipped or have a hashcode already (as you might know the hash code of a String is computed lazy). All of them are new, meaning not yet looked at. The above snippet is the forth execution of String Deduplication, it took 16ms and looked at about 120k Strings. Then you can run the following code with: -Xmx256m -XX:+UseG1GCįor our convenience we do not need to add up all data ourselves but can use the handy totals calculation. So how does this work in practice? First you need the Java 8 Update 20 which was just recently released. For example if a string is not found to have duplicates for a while it will be no longer checked. This whole process of course brings some overhead, but is controlled by tight limits. The first char array then is no longer referenced anymore and can be garbage collected. If they match as well, one String will be modified and point to the char array of the second String. As soon as it finds another String which has the same hash code it compares them char by char. It takes their hash value and stores it alongside with a weak reference to the array. Various strategies for String Duplication have been considered, but the one implemented now follows the following approach: Whenever the garbage collector visits String objects it takes note of the char arrays. String Deduplication takes advantage of the fact that the char arrays are internal to strings and final, so the JVM can mess around with them. With Java 8 Update 20 we now have access to a new feature called String Deduplication, which requires the G1 Garbage Collector and is turned off by default. It is not uncommon to find 30% of the memory consumed by Strings, because not only are Strings the best format to interact with humans, but also popular HTTP APIs use lots of Strings. Especially the char containing the individual UTF-16 characters is contributing to most of the memory consumption of a JVM by each character eating up two bytes. Strings consume a lot of memory in any application.
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