Knowledge Base: Troubleshooting

  • The QuasarDB daemon reports "out of free sessions"

    Summary

    The QuasarDB daemon reports the following error:

    Clients might experience reliability issues, and sessions time out.

    Cause

    All operating systems put limits on the maximum number of file descriptors or TCP connections a process can use. In QuasarDB, each client uses a dedicated connection to each partition it wants to write to. When this error occurs, it means QuasarDB is unable to reserve a new connections for clients.

    Resolution

    Option 1: Ensure sessions are properly cleaned up

    The most effective solution to this is to ensure you are using proper resource management client-side. Ensure that you are tearing down your QuasarDB

  • QuasarDB reports that no entry is in memory, but memory usage is high

    Symptoms

    The QuasarDB daemon log file shows the following message:

    Additionally, QuasarDB shows very high CPU usage.

    Cause

    QuasarDB reports its actual memory usage, which includes internal data structures as well as entries in cache. The daemon is configured in such a way that causes its internal data structures to go beyond the configured limit, leaving no available memory for actual data.

    This causes the QuasarDB daemon to frequently start a cache eviction process, possibly many times per second. This is an expensive operation that causes a very high CPU load, which degrades system performance.

    Resolution

    Option 1: Use the

  • The QuasarDB API reports " An entry matching the provided alias cannot be found."

    Summary

    You are performing operations on a multi-node QuasarDB cluster that are performed in quick succession and depend upon each other. Your code might look like this:

     series.attach_tag('a')  tag = cluster.tag('b')  tag.attach_tag('b')

    While performing the last operation, the QuasarDB client API reports the following error:

    Cause

    The different entries are stored on different nodes within your cluster and you have a clock skew between these nodes. The clock skew causes a lag before the first entry is visible to all nodes, causing a failure when these operations are performed in quick succession. 

    Resolution

    Deploy time synchronization from the same time

  • The QuasarDB daemon reports "chord algorithm stopped as it encountered a logic error"

    Summary

    You are setting up a multi-node cluster, and the you see an error with the following message appears in your qdbd log:

    At least one node in the cluster fails to come online.

    Cause

    This error is thrown when the chord algorithm fails to stabilize because it requires the nodes to be time-synchronized within reasonable limits.

    Resolution

    Deploy time synchronization from the same time source across all nodes in the cluster, and make sure this is synchronized on a frequent basis (we recommend once an hour). We recommend using a time source that is as predictable and available as