I’m using *Neo4j 2.3.0* in *Java*. I have 16 GB RAM, running the code on
MAC OSX Laptop, using "*-Xmx12g -Xms12g*" as VM arguments.
I’ve encountered a “GC overhead limit exceeded” problem in Neo4j Java API.
In order to do experiments with lots of queries, I have a program which
opens a transaction over different query.db's and get the answers of that
from my own framework which is wrapped in an object (It runs a query and
print its running time in a file).
So, for running the query, I don’t use *Cypher*.
For each query I open *two transactions* over a query.db and a data.db,
initialize my framework and run it. The memory usage slightly increases and
the “GC overhead” finally happens.
try (Transaction txG = knowledgeGraph.beginTx()) {
try (Transaction txQ = queryGraph.beginTx()) {
MyObj myFramework = new MyObj();
printTheResultsIntoTheFile(framework.run());
myFramework =null;
txQ.success();
txQ.close();
*These are some of my endeavors to get rid of this error:*
1.
1. After I’ve used a monitoring program to dump the heap, I’ve found
that there is some problem with this “
*org.neo4j.io.pagecache.impl.muninn.MuninnPageCache*” So, I’ve tried to
set the page cache size and limit it to a small value:
2.
1.
dataGraph = new
GraphDatabaseFactory().newEmbeddedDatabaseBuilder(MODELGRAPH_DB_PATH)
.setConfig(GraphDatabaseSettings.pagecache_memory,
"500M").newGraphDatabase();
However, still the "memory leakage” problem exists.
1.
2.
2. After tx.success(), I called the tx.close() to make sure that it
doesn’t use the memory.
3.
3. After using my framework(object) to find the answers of a query, I
explicitly set it to null. topkFramework=null;
4.
4. I called System.gc(); and System.runFinalization();
5.
5. I changed all of my static variables like MyCacheServer or
MyNeighborIndexer to non-static ones and in each query, I made them
clear,
and explicitly set them to null.
queryNodeIdSet.clear(); queryNodeIdSet = null; queryNodeIdSet = new
HashSet<Long>();
3. I've used MemoryAnalyzer (MAT) for eclipse. The biggest object is
*org.neo4j.io.pagecache.impl.muninn.MuninnPage* which got 3.54 GB of
memory. Other objects are ok in my case because of some nodes/relationships
id indexing. (The dataset itself is 3.15 GB, I really don't want this much
of caching)
Could you please help me on this? I've asked this question
<http://stackoverflow.com/questions/35876057/neo4j-java-api-gc-overhead-limit-exceeded-after-running-multiple-queries>
in stackoverflow also.
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