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  1. MariaDB MaxScale
  2. MXS-6102

A busy server is not marked down when only the monitor times out

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    • MXS-SPRINT-252, MXS-SPRINT-263, MXS-SPRINT-264, MXS-SPRINT-265
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      A monitored server may remain in running status if the connection failure was
      due to connection timeout and if MaxScale has recently received data from the
      server in response to a client query. These conditions suggest that the server
      is still running, but too busy to process MaxScale monitor connections.
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      A monitored server may remain in running status if the connection failure was due to connection timeout and if MaxScale has recently received data from the server in response to a client query. These conditions suggest that the server is still running, but too busy to process MaxScale monitor connections.

    Description

      Monitor connectivity and response test may fail due to server being extremely busy. MaxScale should consider the server alive if routers are receiving data from server. Perhaps a special status flag is needed, e.g. "really busy" or "saturated"?

      Currently, the above scenario should not be too threatening, since when a monitor labels a server as [Down], it actually commands all routing connections to that server to hangup. Once this happens, and the server detects that the clients have disconnected, the server would likely close any attached sessions and free resources. This would then lead to the server being available for MaxScale monitor connections once more. At least, this is what would happen with one MaxScale. With multiple MaxScales, a server could be saturated by MXS1 and not connectable by monitor from MXS2.

      This feature can have unintended consequences for monitoring in general, as it changes the logic in how the Running-state of a server is defined.

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            esa.korhonen Esa Korhonen
            johan.wikman Johan Wikman
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