Multiple threads all using the same RexsterGraph instance, each one creates a new vertex then sets many properties on it. Runs against Titan Server (Cassandra) 0.3.2. Exceptions ensue.

app.log

[info] Running com.pongr.RexsterGraphTest 
2013-08-21 13:52:45,721 DEBUG com.pongr.RexsterGraphTest$  - First
2013-08-21 13:52:46,744 DEBUG com.pongr.RexsterGraphTest$  - Started 2 threads, waiting for them to finish...
2013-08-21 13:52:46,982 DEBUG c.pongr.CreateVertexAndSetProperties  - Starting vertex 1 using graph rexstergraph[http://localhost:8182/graphs/graph[titangraph[embeddedcassandra:null]]]...
2013-08-21 13:52:46,982 DEBUG c.pongr.CreateVertexAndSetProperties  - Starting vertex 2 using graph rexstergraph[http://localhost:8182/graphs/graph[titangraph[embeddedcassandra:null]]]...
2013-08-21 13:52:48,117 DEBUG c.pongr.CreateVertexAndSetProperties  - Created v[4] with id 2
2013-08-21 13:52:48,117 DEBUG c.pongr.CreateVertexAndSetProperties  - Created v[8] with id 1
[error] (Thread-2) java.lang.RuntimeException: Server returned HTTP response code: 500 for URL: http://localhost:8182/graphs/graph/vertices/4
java.lang.RuntimeException: Server returned HTTP response code: 500 for URL: http://localhost:8182/graphs/graph/vertices/4
	at com.tinkerpop.blueprints.impls.rexster.RestHelper.post(RestHelper.java:157)
	at com.tinkerpop.blueprints.impls.rexster.RestHelper.postResultObject(RestHelper.java:55)
	at com.tinkerpop.blueprints.impls.rexster.RexsterElement.setProperty(RexsterElement.java:90)
	at com.tinkerpop.blueprints.impls.rexster.RexsterVertex.setProperty(RexsterVertex.java:19)
	at com.pongr.CreateVertexAndSetProperties.run(RexsterGraphTest.scala:13)
	at java.lang.Thread.run(Thread.java:679)
Caused by: java.io.IOException: Server returned HTTP response code: 500 for URL: http://localhost:8182/graphs/graph/vertices/4
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1403)
	at com.tinkerpop.blueprints.impls.rexster.RestHelper.post(RestHelper.java:154)
	at com.tinkerpop.blueprints.impls.rexster.RestHelper.postResultObject(RestHelper.java:55)
	at com.tinkerpop.blueprints.impls.rexster.RexsterElement.setProperty(RexsterElement.java:90)
	at com.tinkerpop.blueprints.impls.rexster.RexsterVertex.setProperty(RexsterVertex.java:19)
	at com.pongr.CreateVertexAndSetProperties.run(RexsterGraphTest.scala:13)
	at java.lang.Thread.run(Thread.java:679)
2013-08-21 13:52:49,869 DEBUG c.pongr.CreateVertexAndSetProperties  - Finished vertex 1

RexsterGraphTest.scala

package com.pongr

import grizzled.slf4j.Logging
import com.tinkerpop.blueprints.Graph
import com.tinkerpop.blueprints.impls.rexster.RexsterGraph
import java.util.concurrent.CountDownLatch

class CreateVertexAndSetProperties(g: Graph, latch: CountDownLatch, id: String, propetyCount: Int) extends Runnable with Logging {
  override def run() {
    debug("Starting vertex %s using graph %s..." format (id, g))
    val v = g.addVertex(null)
    debug("Created %s with id %s" format (v, id))
    v.setProperty("vertexId", id)
    for (i <- 1 to propetyCount) v.setProperty("key" + i, "value" + i)
    latch.countDown()
    debug("Finished vertex %s" format id)
  }
}

object RexsterGraphTest extends App with Logging {
  debug("First")
  Thread.sleep(1000) //let the logging systems warm up

  //val g = new RexsterGraph("http://localhost:8182/graphs/graph")
  def g2() = new RexsterGraph("http://localhost:8182/graphs/graph")
  val threadCount = 2
  val latch = new CountDownLatch(threadCount)
  (1 to threadCount).map(id => new CreateVertexAndSetProperties(g2(), latch, id.toString, 10)).foreach(new Thread(_).start())
  debug("Started %d threads, waiting for them to finish..." format threadCount)
  latch.await()
  debug("Finished")
}