Analytics and Reports: Why do database file usage numbers change based on the window viewed.

The database file usage numbers change if I change the window I am using. If I look at a twelve hour view, my peak usage for TempDB is 389 GB. If I look at that same 12 hour period in a 7 day view, my peak usage for TempDB is 111 Gb. Why do the peak usage numbers differ?
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Answers

  • Hi @gmcquibben

    From this page:
    Viewing values on the graph
    Each graph line represents the performance of a selected object. SQL Monitor plots up to a maximum of 500 data points on each graph and draws straight lines between consecutive points. For short time ranges (less than 10 minutes) the graph displays fewer data points. For longer time ranges (greater than 45 minutes), data is aggregated to make sure that whatever the time range displayed, peaks and troughs are maintained on the graph relative to each other so you don't miss anything important.

    I hope that helps clarify why you are seeing different results on a graph for a larger time range.

    Kind regards,
    Alex
    Product Support Engineer | Redgate Software

    Have you visited our Help Center?
  • gmcquibbengmcquibben Posts: 5 New member
    If the chart is aggregating, then how does that explain the large differences in Peak (Maximum) usage? My peak usage is 389 GB in the 12 hour view and 111 GB in the 7 day view. In addition, the graphical representation of 111 GB is proportional to a prior day's peak usage of 380 GB of usage. This looks to be more of a sampling than a true aggregation.zmtbpxwh99yc.png
  • Alex BAlex B Posts: 673 Rose Gold 5
    edited February 27, 2018 7:19PM
    Hi @gmcquibben

    It's aggregation, not addition, so it's averaging the data in a way that should still maintain the data peaks accurately in relation to each other, which it appears to be doing. Then you are able to zoom in on the peaks to get the more accurate information from the narrower time-frame to the point where you have all the actual sampled data points displayed.

    Kind regards,
    Alex
    Product Support Engineer | Redgate Software

    Have you visited our Help Center?
  • gmcquibbengmcquibben Posts: 5 New member
    Alex,
    How can you say, that the aggregate is measuring the peaks accurately, when the correct peak should be 389 GB and it is displaying the peak at 111 GB? It is only displaying one-third of the correct peak value.
    A Maximum value for a period in time can't change in an aggregation unless you don't include it in the aggregation.
    Greg
  • Hi @gmcquibben

    Apologies, I left off part of the sentence - it should have read - "maintain the data peaks accurately in relation to each other, which it appears to be doing", but even then, accurately may not be the best word to use.

    This sentiment is supposed to be the same as what was indicated in the documentation I linked at first. The values may not be the actual values, but the peaks and troughs should be consistent when you zoom in and out, with the closer in you zoom, getting you closer to the actual values.

    Kind regards,
    Alex
    Product Support Engineer | Redgate Software

    Have you visited our Help Center?
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