Using predict_linear to predict if disk will fill in N hours

[zhug...@gmail.com]

Hey guys,

Here is my current query to get the percentage of disk usage my containers:

container_fs_usage_bytes{device=~"/dev/x.*"} / container_fs_limit_bytes{device=~"/dev/x.*"} * 100

Now, based on this article: I want to use predict_linear to send an alert if the disk looks like its gonna fill in N hours.

Here is the query I've been struggling with (I just want the estimated percentage of disk utilized 4 hours from now): 

predict_linear(container_fs_usage_bytes{device=~"/dev/x.*"} / container_fs_limit_bytes{device=~"/dev/x.*"} * 100, 4 * 3600)

This query returns the following error: Error executing query: parse error at char 124: expected type matrix in call to function "predict_linear", got vector

Can anybody tell me how I am thinking about this wrong? 

Also, is there an easy way to get the type of prometheus value returned by the queries in the GUI tool?

Thanks,

Zach

[Ben Kochie]

If you're trying to write an alerting rule, you probably want something like this:

predict_linear(container_fs_usage_bytes{device=~"/dev/x.*"}[1h]), 4 * 3600) > container_fs_limit_bytes

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[zhug...@gmail.com]

Aaah. Thanks Ben! 

I realized now that keeping the `container_fs_limit_bytes` in the predict_linear function is silly because that is a hard limit...i.e. no need to predict what it will be in 4 hours. 

Thank you for taking the time to write this response, I still need to do some testing but this looks like it is exactly what I was looking for.

On Tuesday, May 29, 2018 at 11:13:33 AM UTC-4, Ben Kochie wrote:

If you're trying to write an alerting rule, you probably want something like this:

predict_linear(container_fs_usage_bytes{device=~"/dev/x.*"}[1h]), 4 * 3600) > container_fs_limit_bytes

On Tue, May 29, 2018 at 4:56 PM, <zhug...@gmail.com> wrote:

Hey guys,

Here is my current query to get the percentage of disk usage my containers:

container_fs_usage_bytes{device=~"/dev/x.*"} / container_fs_limit_bytes{device=~"/dev/x.*"} * 100

Now, based on this article: I want to use predict_linear to send an alert if the disk looks like its gonna fill in N hours.

Here is the query I've been struggling with (I just want the estimated percentage of disk utilized 4 hours from now): 

predict_linear(container_fs_usage_bytes{device=~"/dev/x.*"} / container_fs_limit_bytes{device=~"/dev/x.*"} * 100, 4 * 3600)

This query returns the following error: Error executing query: parse error at char 124: expected type matrix in call to function "predict_linear", got vector

Can anybody tell me how I am thinking about this wrong? 

Also, is there an easy way to get the type of prometheus value returned by the queries in the GUI tool?

Thanks,

Zach

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