CODEWITHSUNDEEP
gremlinjanusgraphtinkerpop3gremlin-servergremlinpython
flotothemoon
flotothemoon

Reputation: 1892

Why is Gremlin Server / JanusGraph ignoring some of my requests?

I'm using the Gremlin Python library to perform traversals on a JanusGraph deployment of Gremlin Server (the same also happens using just Tinkergraph). Some long traversals (with thousands of instructions) don't get a response, no errors, no timeouts, no log entries or errors on the server or client. Nothing.

The conditions for this silence treatment aren't clear. The described behaviour doesn't linearly depend on bytes or number of instructions. For instance, this code will hang forever for me:

g = traversal().withRemote(DriverRemoteConnection('ws://localhost:8182/gremlin', 't'))
g = g.inject("")
for i in range(0, 8000):
    g = g.constant("test")
print(f"submitting traversal with length={len(g.bytecode.step_instructions)}")
result = g.next()
print(f"done, got: {result}") # this is never reached

It doesn't depend on just the number of bytes in the request message since the number of instructions beyond which I don't get response doesn't change even with very large constant values in place of just "test". For instance, injecting 7000 values with many paragraphs of Lorem Ipsum works as expected and returns in a few milliseconds.

While it shouldn't matter (since I should be getting a proper error instead of nothing), I've already increased server-side maxHeaderSize, maxChunkSize, maxContentLength etc. to ridiculously high numbers. Changing the serialization format (e.g. from GraphSONMessageSerializerV3d0 to GraphBinaryMessageSerializerV1) doesn't help either.

Note: I know that very long traversals are an anti-pattern in Gremlin, but sometimes it's not possible or very inefficient to structure traversals such that they can use injected values instead.

Upvotes: 1

Views: 252

Answers (1)

stephen mallette
stephen mallette

Reputation: 46226

I've answered this question on gremlin-users not realizing it was also asked here on StackOverflow. For completeness, I'll duplicate my response here.

The issue is less related to bytes and string lengths and more with the length of the traversal chain (i.e. the number of steps in your traversal). You end up hitting a JVM limit on the stack size on the server. You can increase the stack size on the jvm by changing the size of the -Xss value which should allow you a longer traversal length. That will likely come with the need to re-examine other JVM settings like -Xmx and perhaps garbage collection options.

I do find it interesting that you don't get any error messages though - you should see a stackoverflow somewhere, unless the server is just wholly bogged down by your request. I'd consider throwing more -Xmx at it to see if you can get it to respond with an error at least or to keep an eye on server logs to at least see it surface there.

Upvotes: 1

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