[Lens] Time shift previous period

[ghudgins]

Describe the feature:
Allow time shifts involving date histograms to be previous to the overall time period of the report:

If the date histogram is 30 second intervals and the report is "last 15 minutes" than "previous overall period" would be a 15 minute shift. Today "previous" time shifts when used on date histogram appears to shift back one previous date histogram interval (30 seconds in this case) which I don't believe is as useful given the user can see those values anyway (except one previous period on the end of the histogram)

Describe a specific use case for the feature:
Shifts involving data that's also visible on the range don't seem as useful as an indentical shift to the overall reporting period. So if I dynamically select "3 hours" it would be nice if there was an option that generated the 3 previous hours automatically.

I believe it works this way if you aren't using a date histogram (previous is the previous overall time period)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[ghudgins]

as discussed today, we can use this issue to track bringing previous back to time shifts (since it's been removed). need to answer:

• re-define Previous to be this previous overall idea?
• do we include Previous_bucket to get at the main use case of % growth to previous bucket....could we do this as an option on differences so we don't need this here?

[flash1293]

There is a small difference between time shift previous bucket and something like differences - time shift previous bucket does its own data fetching which means the very first bucket will also have a "previous" one of the data allows it (the bucket which is not in the overall time range anymore).

If we want this, then I think we need a previous_bucket shift (naming tbd - IMHO previous for previous bucket and previous_range for overall previous would be nice). If we don't need it, we can go with a new function used like this (always pulling the data from the previous bucket leaving the first one empty): previous(count()). The previous function would be almost identical to differences and very easy to build.

[flash1293]

Thinking about it, I like the previous(count()) - it clearly separates separate data fetching from calculations looking at other buckets of the same series. If someone really needs the very first one, they can manually keep the shift interval and date histogram interval in sync but I expect that to be an edge case.

[ghudgins]

this issue #62381 shows why we need a "previous bucket" and the "overall previous" time period as distinct options

[ghudgins]

scope this issue for only the "overall previous" or "previous range" concept and created #115776 to account for the bucket-style functionality

[dej611]

I think it would be possible to add the previous support even when a date histogram is declared with the same trick used for #144564 to compute a round interval shift.