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[DOCS] Querying basics: explain range and instant queries 

I often see people ask questions that indicate they don't understand
this point, and launching into "instant vector" and "range vector" is
likely to point them in the wrong direction.

Remove the admonishment that the reader mustn't confuse these things.
Remove mention of "inferred sample timestamps" that is never explained.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This commit is contained in:
Bryan Boreham 2024-07-22 16:17:35 +01:00
parent 398504e080
commit cc7dcf5afe
1 changed files with 10 additions and 6 deletions
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16
docs/querying/basics.md
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@ -8,9 +8,15 @@ sort_rank: 1
Prometheus provides a functional query language called PromQL (Prometheus Query
Language) that lets the user select and aggregate time series data in real
time. The result of an expression can either be shown as a graph, viewed as
tabular data in Prometheus's expression browser, or consumed by external
systems via the [HTTP API](api.md).
time.
When you send a query request to Prometheus, it can be an _instant query_, evaluated at one point in time,
or a _range query_ at equally-spaced steps between a start and an end time. PromQL works exactly the same
in each cases; the range query is just like an instant query run multiple times at different timestamps.
In the Prometheus UI, the "Table" tab is for instant queries and the "Graph" tab is for range queries.
Other programs can fetch the result of a PromQL expression via the [HTTP API](api.md).
## Examples
@ -94,9 +100,7 @@ Examples:
## Time series selectors
Time series selectors are responsible for selecting the times series and raw or inferred sample timestamps and values.
Time series *selectors* are not to be confused with higher level concept of instant and range *queries* that can execute the time series *selectors*. A higher level instant query would evaluate the given selector at one point in time, however the range query would evaluate the selector at multiple different times in between a minimum and maximum timestamp at regular steps.
These are the basic building-blocks that instruct PromQL what data to fetch.
### Instant vector selectors