It depends if it's backend or JVM memory. Generally the backend memory will shrink down when queries aren't executing, but may still occupy a few GB.
If it's JVM memory, then if the memory is actually unused then its really up to the JVM to GC. It's possible that the memory is actually in use storing the catalog - all coordinators store a copy of the catalog cache in memory. If this is the problem, you can use our "dedicated coordinator" feature to reduce the number of impala daemons that are coordinators. If you have 54 nodes, making some impala daemons executors only prevents the catalog cache from being sent to those daemons. Clients won't be able to submit queries to the non-coordinators but I don't think 54 coordinators is necessary for most workloads. See https://impala.apache.org/docs/build/html/topics/impala_scalability.html for more info. > 2) is it a configuration parameter that i can used to disable this? or it a system params that related to the jvm? You can set some JVM parameters via JAVA_TOOL_OPTIONS, but this may not address the problem directly > 3) What is the impact if i will limit the jvm memory per node? will this impact the impala performance? If the JVM memory is too small to fit the catalog cache, you will run into problems - e.g. all queries failing >4) Where this memory used by impala? even it's name indicate it's useless and cann't be used ( What is the purpose of this memory). I don't quite understand this statement. What memory are you referring to? What name? On Thu, May 17, 2018 at 10:32 AM, Fawze Abujaber <fawz...@gmail.com> wrote: > Hi Guys, > > I have a cluster with 54 nodes, i configured the 35 GB for the impala > daemo memory limit, all the time there is ~ 10GB-20GB memory that each > nodes reserved as resident memory. > I'm aware that this memory will not impact the running queries and the > memory limit for impala daemon, but this is a memory that hold by the JVM, > and can impact other services running on the same node like HDFS and > NodeManager. > > My Questions: > > 1) Is there a way to free up this memory without restarting the impala > service? > 2) is it a configuration parameter that i can used to disable this? or it > a system params that related to the jvm? > 3) What is the impact if i will limit the jvm memory per node? will this > impact the impala performance? > 4) Where this memory used by impala? even it's name indicate it's useless > and cann't be used ( What is the purpose of this memory). > > > -- > Take Care > Fawze Abujaber >
