lack of documents on "dbengine multihost disk space"



  • Hi everybody
    I’m very excited about the new update of netdata and want to update all of our parents, but I have some doubts about dbengine multihost disk space, now I have set dbengine disk space = 64 so every child and parent can have 64mb of data on the disk, but what about dbengine multihost disk space? What value should I set for this parameter?
    How is it devided between the parent and child?



  • Have a look at https://learn.netdata.cloud/docs/agent/database/engine

    The dbengine disk space is the deprecated legacy option. The dbengine multihost disk space is the disk space. The RAM cache is page cache size.



  • @zack Thank you for your reply but I’m, still confused, our parent server is currently storing metrics from 60 children, so I know dbengine disk space = 64 means each child can have up to 64mb of the parent’s storage. but when I set dbengine multihost disk space to 64mb in the parent server, netdata becomes unavailable after 3 to 4 hours. my guess is, it means that the parent and the children can have 64mb of storage in total


  • Staff

    You’re correct that if you set dbengine multihost disk space to 64 on the parent server, you’re allocating a shared 64 MiB for all your nodes, which isn’t enough.

    Can you try using our dbengine calculator again, if you haven’t already? https://learn.netdata.cloud/docs/agent/database/calculator

    I updated the calculator yesterday with help from engineering to help give better and more useful numbers with the new multihost configuration. Make sure you set those 60 child nodes so you can start getting an estimate for how much disk to allocate to your metrics and the suggested dbengine multihost disk space setting. Maybe post your result here so we can discuss further?

    Another option would be set dbengine multihost disk space to 3840, which would allocate exactly the same amount of disk space as you had before.



  • @joel Thanks for your reply, so if my parent server has 300Gb of storage, I can set the dbengine multihost disk space to 250Gb and as we add new children to this parent, the history of the metrics become less, right?
    But what about the ram usage? should we expect more ram usage because the dbengine now has the value of 250Gb? (In the legacy dbengine, all dbengines used 3904Mb of the disk)


  • Staff

    The new multihost database shouldn’t take up more disk space (or RAM) than before. I just needs to be configured differently.

    I would recommend you set dbengine multihost disk space = 4000 and see what kind of metrics retention that gives you. And yes, you’re right that as you add new children, the history will shrink, as more nodes are sharing the same pool of resources.



  • In this case, I have to restart netdata parent with new dbengine multihost disk space if my children keep growing since I need to keep metrics of the children at least for 1 day


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