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The optimal setting for the heap memory on AWS for Neo4J 3.5

Graph Buddy

I run Neo4J 3.5 on an AWS EC2 instance.

Suppose the instance has 4Gb of RAM. As I understand, if I leave all the settings default, the neo4j.template (which then becomes neo4j.conf upon launch) allocates about 50% of this RAM to the heap (via dbms.memory.heap.max_size and then about 50% of the remaining (that is, 25%) to dbms.memory.pagecache.size.

But then is the heap memory limited by the maximum heap memory setting in Java? For instance, when I check it using

java -XshowSettings:vm

I can see my max heap is 1G. I can increase it to 2G but will it also make more heap available to Neo4J in the automatic mode?

How can I check, on an instance running on AWS (via systemctl) how much heap was actually allocated upon launch to the neo4j process?



Have you looked at what the neo4j memory recommendation diagnostic recommends? it has some tips and notes as well.

The command is

neo4j-admin memrec

here is an example output of memrec

I have no name!@67d76e91f1c9:/var/lib/neo4j$ neo4j-admin memrec
# Memory settings recommendation from neo4j-admin memrec:
# Assuming the system is dedicated to running Neo4j and has 61400m of memory,
# we recommend a heap size of around 23000m, and a page cache of around 26600m,
# and that about 11800m is left for the operating system, and the native memory
# needed by Lucene and Netty.
# Tip: If the indexing storage use is high, e.g. there are many indexes or most
# data indexed, then it might advantageous to leave more memory for the
# operating system.
# Tip: The more concurrent transactions your workload has and the more updates
# they do, the more heap memory you will need. However, don't allocate more
# than 31g of heap, since this will disable pointer compression, also known as
# "compressed oops", in the JVM and make less effective use of the heap.
# Tip: Setting the initial and the max heap size to the same value means the
# JVM will never need to change the heap size. Changing the heap size otherwise
# involves a full GC, which is desirable to avoid.
# Based on the above, the following memory settings are recommended:

note: This neo4j is running on an AWS EC2 host with 64g of ram but inside a docker container, which is why it says "I have no name!" where we usually see the hostname. I shelled into the container to run the memrec command.