On Jan 4, 2018 11:14 PM, "Rainer Jung" <rainer.j...@kippdata.de> wrote:
Am 04.01.2018 um 18:20 schrieb Christopher Schultz: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > Ambica, > > On 1/4/18 11:17 AM, Sanka, Ambica wrote: > >> I am seeing below highlighted errors in native_err logs in all my >> tomcat applications. I also increased memory for the VM from 4GB to >> 8GB. Still seeing those. When do we get that errors? I am reading >> online that when program asks for memory and java cannot give, >> that's when we see them. Please suggest. Java HotSpot(TM) 64-Bit >> Server VM (25.20-b23) for linux-amd64 JRE (1.8.0_20-b26), built on >> Jul 30 2014 13:13:52 by "java_re" with gcc 4.3.0 20080428 (Red Hat >> 4.3.0-8) Memory: 4k page, physical 8061572k(2564740k free), swap >> 4063228k(4063228k free) >> >> CommandLine flags: -XX:+HeapDumpOnOutOfMemoryError >> -XX:HeapDumpPath=/opt/apache/ancillariesmonitoring/logs/ >> -XX:InitialHeapSize=128985152 -XX:MaxHeapSize=268435456 >> -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+UseCompressedClassPointers >> -XX:+UseCompressedOops -XX:+UseParallelGC >> > > Others have commented on those messages you received, but nobody > mentioned your heap configuration. In the above command-line > arguments, you have specified both the minimum and maximum heap > memory. You have expressed those values in bytes which makes it > somewhat hard to read what they actually are, but this is what you > I *think* the JVM top line in GC output always shows bytes, even if you were using other units in the original switches. I agree. have in readable units: > > - -XX:InitialHeapSize=128M -XX:MaxHeapSize=256M > but yes, that is a valid point! So you aren't using an 8GiB heap. You aren't even using a 4GiB heap. > You are using a 256 *megabyte* heap. If you really want an 8GiB heap, > you'll need to set it properly in your command-line arguments. > > Note that setting the initial heap size to anything other than the > maximum heap size just makes the JVM take longer to get the heap > generations sized appropriately. For a long-running server process, I > think it never makes any sense to set initial < max heap size. Always > set them to the same value so that the heap itself does not have to be > expanded/resized during heap allocations. Christopher, I really never found any explanation behind this "initial=max" heap size theory until I saw your mail; although I see this type of configuration in most of the places. It will be awesome if you can tell more about benefits of this configuration. I usually do not set initial and max heap size to same value because garbage collection is delayed until the heap is full. Therefore, the first time that the GC runs, the process can take longer. Also, the heap is more likely to be fragmented and require a heap compaction. To avoid that, till now my strategy is to: - Start application with the minimum heap size that application requires - When the GC starts up, it runs frequently and efficiently because the heap is small - When the heap is full of live objects, the GC compacts the heap. If sufficient garbage is still not recovered or any of the other conditions for heap expansion are met, the GC expands the heap. Another thing, what if I know the server load varies a lot(from 10s in night time to 10000s during day time) during different time frame, does "initial=max heap" apply for that situation also? Please let me know what you think about it. Thanks! Suvendu
