This page explains some of the behaviors that you might see when using metrics collected by your Google Cloud projects.
Gaps in chart data
Charts occasionally exhibit gaps in the data. For example, the following
screenshot illustrates this behavior for the metric
Gaps in the data can occur when data is written very infrequently. Cloud Monitoring collects metrics by sampling, and with very sparse data, there might not be any data available when a sample is collected. For example, gaps in load-balancer metrics might occur when the request count is 0.05 queries per second (QPS) or less. When the query rate increases, the gaps disappear.
Alert chart doesn't display any data
A dashboard contains an alert chart, but it doesn't display any data.
To resolve this situation, try the following:
View the configuration of the alert chart and ensure an alerting policy is selected. If no alerting policy is displayed, then associate the alert chart with an alerting policy or delete the alert chart from the dashboard.
If an alert chart is added to a dashboard and then the referenced alerting policy is deleted, then the alert chart stops displaying data. Deleting an alerting policy doesn't delete alert charts that reference that policy.
View the details of the alerting policy and verify that it contains a single condition.
If an alert chart is added to a dashboard and then the referenced alerting policy is modified to contain multiple conditions, then the alert chart stops displaying data. To resolve this condition, associate the alert chart with a single-condition alerting policy or delete the alert chart from the dashboard.
Increase the period of time-range. The time range selector must be set to a value longer than the sampling period of the data. While most metrics are sampled every 60 seconds, some metrics are sampled infrequently. For example, the serviceruntime.googleapis.com/quota/limit metric is sampled every 86,400 seconds (1 day).
Chart with multiple metrics displays an error message
You are configuring a chart to display multiple metrics and the chart displays the following error message:
The units for queries using the same Y-axis must be the same for the chart to render correctly.
This error message indicates that a chart has at least two metrics mapped to the same Y-axis, but the units of those time series are different. For example, a chart is configured to display a metric that is reported as a percentage and a metric that reports a count.
To resolve this error, do the following:
If your chart contains metrics with more than two unit types, then remove metrics until you have only two unit types.
Assign all metrics with one unit type to the left Y-axis and all metrics with the other unit type to the right Y-axis.