Hi, In the course of a tuning exercise to decruft a Cassandra installation infected with "Tuning By Folklore" hacks, I found this beauty.
The folklore suggests setting the JVM flag -XX:+PerfDisableSharedMem as per http://www.evanjones.ca/jvm-mmap-pause.html (tl;dr Writing some hsperfdata memory statistics can block against kernel performing disk I/O). Setting the flag is intended to reduce large outliers in the GC tail and other gremlins (because this contention can occur during any safepoint operation). All seems reasonable so far. Reading the comments and doing some other detective work leads to the possibility that the lazytime Linux mount option may remove the need to set the option, by removing the contention. However, there appears to be no direct confirmation of this, and, rather amusingly, the combination of search terms "lazytime PerfDisableSharedMem" produces no Google results at all - not something I thought I'd ever see in the year 2019. Any thoughts or pointers gratefully received. Thanks, Ben -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to mechanical-sympathy+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/mechanical-sympathy/CABKW8RjjXUM2Vq2BF2RXqBA1EscgxE2-XuAP195vRd4eN4V-4g%40mail.gmail.com.
