Parameterize lookback in PromQL

[waynexia]

What problem does the new feature solve?

Prometheus now supports to set lookback per query prometheus/prometheus#9946

In our framework, this parameter is defaulted to 5m and can't be overridden per query at present

greptimedb/src/query/src/parser.rs

Lines 39 to 40 in a218f12

	const DEFAULT_LOOKBACK: u64 = 5 * 60; // 5m
	pub const DEFAULT_LOOKBACK_STRING: &str = "5m";

But the underlying planner does have a parameter

greptimedb/src/promql/src/planner.rs

Lines 83 to 88 in a218f12

	struct PromPlannerContext {
	// query parameters
	start: Millisecond,
	end: Millisecond,
	interval: Millisecond,
	lookback_delta: Millisecond,

What does the feature do?

Support setting lookback per query as well.

Prometheus hasn't exposed this to HTTP API, so we only need to change the TQL part for now.

Specifically, makes TQL accept the new fourth optional parameter for lookback and handle it in the planner:

TQL EVAL (<start>, <end>, <step>, [lookback]) <promql>

Implementation challenges

No response

[yuanbohan]

With this feature, we can have the ability to use PromQL to query exact data with no false result via setting lookback_delta=0, exciting 🚀

[etolbakov]

I don’t want to overcommit but ideally I’d like to do this one as well.
As a part of #3452 I’m changing the Tql query parsing (#3507)

[tisonkun]

@etolbakov Cool! Feel free to link this issue in your PR like closes #3453.

[tisonkun]

@waynexia BTW I wonder what is the difference between the code path of PromQL and TQL. Seems it's quite a bit undocumented.

[waynexia]

This is not part of #3492.

what is the difference between the code path of PromQL and TQL

They are the same after parser phase

[tisonkun]

Is this closed by #3630?

cc @etolbakov @waynexia

[etolbakov]

yeah, let's close it @tisonkun
Thank you!