Yigit Kiran created TINKERPOP-2169:
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Summary: Responses exceeding maxContentLength cause subsequent
queries to hang
Key: TINKERPOP-2169
URL: https://issues.apache.org/jira/browse/TINKERPOP-2169
Project: TinkerPop
Issue Type: Bug
Components: driver
Affects Versions: 3.4.0
Environment: Client: EC2 Amazon Linux t3.medium
Server: Amazon Neptune r4.2xlarge
Reporter: Yigit Kiran
Gremlin Driver replaces connections on the channel when it receives Exceptions
that are instances of IOException or CodecException (including
CorruptedFrameException). When CorruptedFrameException is thrown because
response length is greater than the maxContentLength value (32kb by default),
driver thinks the host might be unavailable and tries to replace Connection.
If Connection is shared among multiple requests (its pending queue is > 1),
other WSConnection goes stale after connection replacement, while keeping the
server executor threads busy.
Keeping the exec threads busy for stale connections prevents server from
picking up new tasks for subsequent requests from the request queue.
Additionally since there is a new connection added in Client, it can accept
more requests and similar errors can lead to a build up in request queue. When
many concurrent requests gets into this situation server become unresponsive to
the new requests.
h3. Steps to repro
1. Have a gremlin server
2. Connect it using java driver with setting the maxContentLength pretty low,
i.e. using the config below:
{code:java}
Cluster.Builder builder = Cluster.build();
builder.addContactPoint(endpoint[0]);
builder.port(8182);
builder.maxConnectionPoolSize(100);
builder.maxSimultaneousUsagePerConnection(100);
builder.maxInProcessPerConnection(50);
builder.maxContentLength(32); // <-- this is reduced from 32k
builder.keepAliveInterval(0);
{code}
3. Issue concurrent requests using the cluster, where the response would be
greater than 32 bytes.
h3. Ideas on a possible solution
One possible solution to this is to not consider channel as dead when request
length exceeds maxContentFrame length.
{{}}
{code:java}
final class Connection {
...
public ChannelPromise write(final RequestMessage requestMessage, final
CompletableFuture<ResultSet> future) {
...
// FIX HERE: Do not consider CorruptedFrameException as non-recoverable
exception.
if ((t instanceof IOException || t instanceof CodecException) && (! (t
instanceof CorruptedFrameException))) {
...
}
}
}
{code}
Another fix could be the request can be deleted from the Connections' pending
request map, and if there are other pending requests on the connection, close
them before replacing the connection, or not replace the connection at all:
{code:java}
final class Connection {void replaceConnection(final Connection connection) {
...
// FIX HERE: Do not replace connection if there are pending requests on it.
if (!connection.getPending().isEmpty()) {
return; // prevent replacing the connection while there are pending
requests.
}
considerNewConnection();
definitelyDestroyConnection(connection);
}
}{code}
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