Neo4j fails to respond

[Eric Fulton]

I'm using Neo4j 2.3.3 and spring-data-neo4j in a highly threaded environment where I attempt lots of reads/writes, and I often get 

NoHttpResponseException (which means neo didn't respond).  This happens most frequently on reads when I'm using a 

Neo4jOperations object to load domain objects to a certain depth.

Is it possible that neo would drop/refuse connections under moderate/heavy load, or is this more likely a problem with spring-data-neo4j, OR
is there some third possibility?  Just for reference, here's an example stack trace:

........

Caused by: org.neo4j.ogm.session.result.ResultProcessingException: Failed to execute request: {"statements":[{"statement":"MATCH (n:Widget) WHERE n.widgetId = {widgetId} RETURN n","parameters":{"partNumber":"146300"},"resultDataContents":["graph"],"includeStats":false}]}

at org.neo4j.ogm.session.request.DefaultRequest.execute(DefaultRequest.java:105)

at org.neo4j.ogm.session.request.SessionRequestHandler.execute(SessionRequestHandler.java:99)

at org.neo4j.ogm.session.request.SessionRequestHandler.execute(SessionRequestHandler.java:56)

at org.neo4j.ogm.session.delegates.ExecuteQueriesDelegate.executeAndMap(ExecuteQueriesDelegate.java:118)

at org.neo4j.ogm.session.delegates.ExecuteQueriesDelegate.query(ExecuteQueriesDelegate.java:76)

at org.neo4j.ogm.session.delegates.ExecuteQueriesDelegate.queryForObject(ExecuteQueriesDelegate.java:50)

at org.neo4j.ogm.session.Neo4jSession.queryForObject(Neo4jSession.java:330)

at org.springframework.data.neo4j.template.Neo4jTemplate.queryForObject(Neo4jTemplate.java:290)

... 28 common frames omitted

Caused by: org.apache.http.NoHttpResponseException: dev-funzone:7474 failed to respond

at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:143)

at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57)

at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:261)

at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:165)

at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:167)

at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:272)

at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:124)

at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:271)

at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)

at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)

at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)

at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)

at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)

at org.neo4j.ogm.session.request.DefaultRequest.execute(DefaultRequest.java:80)

... 35 common frames omitted

[Eric Fulton]

The latest version of OGM addresses neo4's flakiness by adding in "retry" functionality for these specific exceptions.  I haven't seen it since upgrading.