what does 'duration' mean in downsample?

[localvar]

Describe your question

From this document, I see there's a duration (after with), and the document says it must be smaller than the duration of the corresponding retention policy.

But I cannot understand its meaning, does it mean the down sampled data will only be kept to that duration?

If yes, and if raw data was deleted after down sample, because this duration is smaller than the duration of the retention policy, then history data will always be deleted earlier before it reach the duarion of the retention policy. I don't think this make sense.

If raw data was not deleted after down sample and will be kept until the duration of the retention policy, then the down sample result becomes an extra copy of the data, that's down sample can never reduce storage requirements.

BTW1: the document says there' should be a watermark in the syntax, but after I checked 'sql.y', I think it should not be there.

BTW2: the document says nothing about where the down sample result will be, while in my experiment, the raw data was deleted but no down sample data was generated.

[xiangyu5632]

reference to the downsample instroduction

[localvar]

reference to the downsample instroduction

Thanks, but the URL is a local one, its host is 'localhost'.