GraphDB OutOfMemoryError: Java heap space - graphdb

Question

I'm using GraphDb Free 8.6.1 in research project, I'm running it with default configuration on linux server having 4GB memory in total.
Currently, we execute quite many CRUD operations in tripplestore.
GraphDB throwed exception in console:
java.lang.OutOfMemoryError: Java heap space
-XX:OnOutOfMemoryError="kill -9 %p"
Executing /bin/sh -c "kill -9 1411"...
Looking into process, GraphDB runs with parameter XX:MaxDirectMemorySize=128G
I was not able to changed, even with ./graph -Xmx3g, process is still running with XX:MaxDirectMemorySize=128G.
I've tried to configure ./grapdh parameter, setting the GDB_HEAP_SIZE=3072m, now process runs with additional -Xms3072m -Xmx3072m parameters, but remains XX:MaxDirectMemorySize=128G.
After update to GDB_HEAP_SIZE=3072m, repository went down again without .hprof file, no exception, nothing suspicious in logs. The following line was flushed into console: Java HotSpot(TM) 64-Bit Server VM warning:
Java HotSpot(TM) 64-Bit Server VM warning: INFO: os::commit_memory(0x00007f5b4b6d0000, 65536, 1) failed; error='Cannot allocate memory' (errno=12)
Please, can you help me to properly configure GraphDB tripplestore to get rid of the Heap Space exceptions?
Thank you.

Answer 1

By default, the value of the -XX:MaxDirectMemorySize (off heap memory) parameter in the JVM is equal to the -XMx (on heap memory). For very large repositories the size of the off heap memory may become insufficient so the GraphDB developers made this parameter 128GB or unlimited.
I suspect that your actual issue is actually allocating too much on heap memory, which leaves no space for the off heap in the RAM. When the database tries to allocate off heap RAM you hit this low OS-level error 'Cannot allocate memory'.
You have two options in solving this problem:
Increase the RAM of the server to 8GB and keep the same configuration - this would allow the 8 GB RAM to be distributed: 2GB (OS) + 3GB (on heap) + 3GB (off heap)
Decrease the -Xmx value to 2GB so the 4GB RAM will be distributed: 1GB (OS) + 2GB (on heap) + 1GB (off heap)
To get a good approximation how much RAM GraphDB needs please check the hardware sizing page:
http://graphdb.ontotext.com/documentation/8.6/free/requirements.html