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https://issues.apache.org/jira/browse/TINKERPOP-2531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17299666#comment-17299666
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ASF GitHub Bot commented on TINKERPOP-2531:
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radu-iviniciu opened a new pull request #1404:
URL: https://github.com/apache/tinkerpop/pull/1404
Link to Jira ticket: https://issues.apache.org/jira/browse/TINKERPOP-2531
DESCITPTION:
If the server becomes unavailable for a period of time the connection
pool might not be able to recreate a connection right after it closes. Even
with a few retries with a backoff to recrete the connections, it might not be
enough and the connections end up being removed from the _deadConnections array
and never end up as valid ones in the _connections array.
This change tries to account for that, and, despite the caller getting a
ServerUnavailableException, if the caller chooses to continue using the
GremlinClient it already has, the ConnectionPool will try to restore itself.
Alternatives considered:
- Once the server is deemed unavailable we could leave it up to the
caller to handle it and potentially recreate the GremlinClient. In that case
this change would not be needed and the only improvement might be to better
document that ServerUnavailableException means that the connection will most
likely not be restored even if the server becomes available again.
Chose this approach over the alternative since it seems like a feature
that a ConnectionPool should have. If done on the caller side it might end
having to implement a logic very similar to the one in the ConnectionPool
itself just centered around GremlinClients rather than websocket connections.
TESTING:
- Tested in our project setup with a Gremlin Client aimed at an AWS Neptune
instance. Manually interrupted the connection / restarted or modified the
instance to observe reconnecting behavior.
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> Gremlin .NET driver ConnectionPool can remain without connections if server
> is down for 1-2 minutes
> ---------------------------------------------------------------------------------------------------
>
> Key: TINKERPOP-2531
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2531
> Project: TinkerPop
> Issue Type: Bug
> Affects Versions: 3.4.10
> Reporter: Radu Iviniciu
> Priority: Major
>
> We are using Gremlin .NET client to connect to AWS Neptune.
> If the server is down for even just 1 - 2 minutes (E,.g. Instance reboot)
> the connection pool can remain without any healthy connections permanently
> even after the server comes back up again.
> Tracked this down to here:
> https://github.com/apache/tinkerpop/blob/60bfc90ce43567d609b1165989c1c74ce825109b/gremlin-dotnet/src/Gremlin.Net/Driver/ConnectionPool.cs#L154
> If the server was not ready yet and the connections were not restored as part
> of the previous TryGetAvailableConnection then the connection pool will
> remain empty indefinitely and all connections are dead even after the server
> is back up.
> Is this longer-ish downtime a use case the client should handle ? Or is it
> expected behavior and we should let the caller handle the
> ServerUnavailableException, potentially recreate the GremClient altogether ?
> What do you guys think ? If this is something the client should handle I can
> take a stab at it and put up a PR.
> Thank you.
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