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docs: Improve documentation of promql-delayed-name-removal flag

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This fixes a formatting problem (`__name__`) was rendered in boldface
without the underscores in the headline).

Furthermore, it explains the possible issues with the feature flag
(change of behavior of certain "weird" queries, problems when
disecting a query manually or in PromLens).

Signed-off-by: beorn7 <beorn@grafana.com>
This commit is contained in:
beorn7 2025-01-22 14:04:14 +01:00
parent e8fab32ca2
commit 2033713757
1 changed files with 13 additions and 1 deletions
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14
docs/feature_flags.md
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@ -131,7 +131,7 @@ Note that during this delay, the Head continues its usual operations, which incl
Despite the delay in compaction, the blocks produced are time-aligned in the same manner as they would be if the delay was not in place.
## Delay __name__ label removal for PromQL engine
## Delay `__name__` label removal for PromQL engine
`--enable-feature=promql-delayed-name-removal`
@ -139,6 +139,18 @@ When enabled, Prometheus will change the way in which the `__name__` label is re
This allows optionally preserving the `__name__` label via the `label_replace` and `label_join` functions, and helps prevent the "vector cannot contain metrics with the same labelset" error, which can happen when applying a regex-matcher to the `__name__` label.
Note that evaluating parts of the query separately will still trigger the
labelset collision. This commonly happens when analyzing intermediate results
of a query manually or with a tool like PromLens.
If a query refers to the already removed `__name__` label, its behavior may
change while this feature flag is set. (Example: `sum by (__name__)
(rate({foo="bar"}[5m]))`, see [details on
GitHub](https://github.com/prometheus/prometheus/issues/11397#issuecomment-1451998792).)
These queries are rare to occur and easy to fix. (In the above example,
removing `by (__name__)` doesn't change anything without the feature flag and
fixes the possible problem with the feature flag.)
## Auto Reload Config
`--enable-feature=auto-reload-config`