Bug: query_range interval parameter broken when query contains filter expressions

[jfolz]

Describe the bug
If the LogQL query contains a filter expression (|=, |~, !=, ...) calls to the query_range API return the same result, regardless of whether the interval parameter set or not and what value it has. E.g. no interval, interval=60s, interval=60000s.

To Reproduce
Steps to reproduce the behavior:

1. Call query_range API with a high volume query (several lines per second) and interval=60s
2. Add filter expression that matches every line |~ ".*" and repeat.
3. Observe that returned log lines are not equal

Expected behavior
Interval should work as documented (i.e., return approximately one line per interval), regardless of the query.

Environment:

• Infrastructure: bare-metal
• Deployment tool: systemd service

$ loki-linux-amd64 -version
loki, version 2.4.2 (branch: HEAD, revision: 525040a32)
  build user:       root@5d9e7a4c92e6
  build date:       2022-01-12T16:48:53Z
  go version:       go1.16.2
  platform:         linux/amd64

Screenshots, Promtail config, or terminal output
As seen here in these examples, without the filter expression the difference in timestamps is ~74 seconds. Once the filter is added to the query the returned lines are only 4000ns apart. Removing the interval parameter with the filter in place yields the same result.

$ curl -s -G -H 'X-Scope-OrgID: <tenant>' \
 --data-urlencode 'start=1646843100000000000' \
 --data-urlencode 'end=1646903100000000000' \
 --data-urlencode 'interval=60s' \
 --data-urlencode 'limit=5000' \
 --data-urlencode 'query=<query>' \
 'http://127.0.0.1:3117/loki/api/v1/query_range' | jq '.data.result[0].values [0,1]'
[
  "1646903089664581496",
  "<result 0>"
]
[
  "1646903015429412821",
  "<result 1>"
]

$ curl -s -G -H 'X-Scope-OrgID: <tenant>' \
 --data-urlencode 'start=1646843100000000000' \
 --data-urlencode 'end=1646903100000000000' \
 --data-urlencode 'interval=60s' \
 --data-urlencode 'limit=5000' \
 --data-urlencode 'query=<query> |~ ".*"' \
 'http://127.0.0.1:3117/loki/api/v1/query_range' | jq '.data.result[0].values [0,1]'
[
  "1646903089664581496",
  "<result 0>"
]
[
  "1646903089664577339",
  "<result 1>"
]

$ curl -s -G -H 'X-Scope-OrgID: tnguyen' \
> --data-urlencode 'start=1646843100000000000' \
> --data-urlencode 'end=1646903100000000000' \
> --data-urlencode 'limit=5000' \
> --data-urlencode 'query=<query> |~ ".*"' \
> 'http://127.0.0.1:3117/loki/api/v1/query_range' | jq '.data.result[0].values [0,1]'
[
  "1646903089664581496",
  "<result 0>"
]
[
  "1646903089664577339",
  "<result 1>"
]

[chaudum]

Hey @jfolz Thanks for reporting the bug. I am able to reproduce the issue and working on a fix.