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Florian Hockmann commented on TINKERPOP-2148:
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OK, no problem. I now added a change for this [in the PR for
TINKERPOP-2135|https://github.com/apache/tinkerpop/pull/1077] as it was already
necessary to change the collection type for that. That PR adds a custom
copy-on-write collection that uses an array as the underlying collection type.
This made it possible to add round-robin scheduling instead of the current
approach of searching for the least used connection which easily produces the
exception you described here (if the {{MaxInProcessPerConnection}} limit is set
to a small value). So, the approach is pretty similar to what you suggested
here, just without modifying the collection all the time via enqueue/dequeue.
> "no connection available!" is being thrown despite lots of free connections
> ---------------------------------------------------------------------------
>
> Key: TINKERPOP-2148
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2148
> Project: TinkerPop
> Issue Type: Bug
> Components: dotnet
> Affects Versions: 3.4.0
> Environment: Windows 10, C#, .NET Core, CosmosDB Graph
> Reporter: Zaoshi
> Assignee: Florian Hockmann
> Priority: Minor
>
> I am submitting multiple graph queries in parallel but in some cases it
> starts throwing this exception:
> {{Gremlin.Net.Driver.Exceptions.NoConnectionAvailableException : no
> connection available!}}
> {{ at Gremlin.Net.Driver.ConnectionPool.GetAvailableConnectionAsync()}}
> {{ at Gremlin.Net.Driver.GremlinClient.SubmitAsync[T](RequestMessage
> requestMessage)}}
> When GremlinClient is initialized with \{PoolSize = 1,
> MaxInProcessPerConnection = 8} everything works fine, however, with
> \{PoolSize = 8, MaxInProcessPerConnection = 1} it starts throwing those
> exceptions even though this connection pool should have same throughput. I
> have tried to increase pool to \{PoolSize = 128, MaxInProcessPerConnection =
> 1} but GremlinClient started to fail even more.
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