Why does ElasticSearch Heap Size not return to normal?

Question

I have setup elasticsearch and it works great.

I've done a few bulk inserts and did a bit of load testing. However, its been idle for a while and I'm not sure why the Heap size doesn't reduce to about 50mb which is what it was when it started? I'm guessing GC hasn't happened?

Please note the nodes are running on different machines on AWS. They are all on small instances and each instance has 1.7GB of RAM.

Any ideas?

Answer 1

Probably. Hard to say, the JVM manages the memory and does what it thinks is best. It may be avoiding GC cycles because it simply isn't necessary. In fact, it's recommended to set mlockall to true, so that the heap is fully allocated at startup and will never change.

It's not really a problem that ES is using memory for heap...memory is to be used, not saved. Unless you are having memory problems, I'd just ignore it and continue on.

Answer 2

ElasticSearch and Lucene maintains cache data to perform fast sorts or facets.

If your queries are doing sorts, this may increase the Lucene FieldCache size which may not be released because objects here are not eligible for the GC. So the default threshold (CMSInitiatingOccupancyFraction) of 75% do not apply here.

Answer 3

您可以按以下说明管理FieldCache持续时间： http : //www.elasticsearch.org/guide/en/elasticsearch/reference/current/index-modules-fielddata.html