Loki should allow empty selector queries

[simonswine]

Describe the solution you'd like

Currently loki requires having at least a single non empty selector (queries require at least one regexp or equality matcher that does not have an empty-compatible value. For instance, app=~".*" does not meet this requirement, but app=~".+" will).

I think this is an unnecessary hurdle for new user and I think we rather should:

• Provide some extra help how a user can add labels to process a query quicker. (E.g. when the UI takes longer than 5 seconds suggest to shring down the result set by label x, y,z
• Workarounds do exists today to get {} (by using a label that all streams have like {namespace=~'.+'})

Describe alternatives you've considered

Leave it as it is, while improving error message (like in #6936 )

[robertomanfreda]

Can you please explain how the workaround should be implemented?

Currently I'm getting the same error on this query {project="$Project", commit="$Commit", container="$Container"} |= ""

I tried with {namespace=~".+", project="$Project", commit="$Commit", container="$Container"} |= "" as you suggested but the error is still present.

I also tried to pass a static selector like {namespace="default", project="$Project", commit="$Commit", container="$Container"} |= "" but no improvements.

[gtirloni]

@robertomanfreda your issue seems to be with |= "" not in the labels.

[voidquark]

Any news ?

[johann-petrak]

When first using loki the refusal to give back all results for an empty query was very surprising and annoying, especially since there are many examples on the internet and I believe even in the Loki docs where "{}" is used to retrieve all entries.

Anyone coming from practically any other query language will assume that query is equivalent to something like a where clause and assume that omitting the constraint will give back everything.

[dan-passaro-dc]

I agree. It should be a configuration option if there's some performance reason for this. As a new user testing out Grafana and Loki locally, I want to view all the data it has so I can see if any of my application's messages are being sent successfully. It's very confusing to determine if I can't see messages because there's no data in Loki or because my query doesn't return results.