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docs: formatting and typo fixes to 3.0 migration guide 

Signed-off-by: Fiona Liao <fiona.liao@grafana.com>
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Fiona Liao 2 weeks ago
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      docs/migration.md

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docs/migration.md
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@ -29,8 +29,8 @@ This document offers guidance on migrating from Prometheus 2.x to Prometheus 3.0
`https://example.com/metrics` or `http://exmaple.com/metrics` to be `https://example.com/metrics` or `http://exmaple.com/metrics` to be
represented as `https://example.com/metrics:443` and represented as `https://example.com/metrics:443` and
`http://example.com/metrics:80` respectively, add them to your target URLs `http://example.com/metrics:80` respectively, add them to your target URLs
- `agent` - `agent`
Instead use the dedicated `--agent` cli flag. Instead use the dedicated `--agent` CLI flag.
Prometheus v3 will log a warning if you continue to pass these to Prometheus v3 will log a warning if you continue to pass these to
`--enable-feature`. `--enable-feature`.
@ -55,37 +55,37 @@ This document offers guidance on migrating from Prometheus 2.x to Prometheus 3.0
- The `.` pattern in regular expressions in PromQL matches newline characters. - The `.` pattern in regular expressions in PromQL matches newline characters.
With this change a regular expressions like `.*` matches strings that include With this change a regular expressions like `.*` matches strings that include
`\n`. This applies to matchers in queries and relabel configs. For example the `\n`. This applies to matchers in queries and relabel configs. For example the
following regular expressions now match the accompanying strings, wheras in following regular expressions now match the accompanying strings, whereas in
Prometheus v2 these combinations didn't match. Prometheus v2 these combinations didn't match.
| Regex | Additional matches | | Regex | Additional matches |
| ----- | ------ | | ----- | ------ |
| ".*" | "foo\n", "Foo\nBar" | | ".*" | "foo\n", "Foo\nBar" |
| "foo.?bar" | "foo\nbar" | | "foo.?bar" | "foo\nbar" |
| "foo.+bar" | "foo\nbar" | | "foo.+bar" | "foo\nbar" |
If you want Prometheus v3 to behave like v2 did, you will have to change your If you want Prometheus v3 to behave like v2 did, you will have to change your
regular expressions by replacing all `.` patterns with `[^\n]`, e.g. regular expressions by replacing all `.` patterns with `[^\n]`, e.g.
`foo[^\n]*`. `foo[^\n]*`.
- Lookback and range selectors are left open and right closed (previously left - Lookback and range selectors are left open and right closed (previously left
closed and right closed). This change affects queries when the evaluation time closed and right closed). This change affects queries when the evaluation time
perfectly aligns with the sample timestamps. For example assume querying a perfectly aligns with the sample timestamps. For example assume querying a
timeseries with even spaced samples exactly 1 minute apart. Before Prometheus timeseries with evenly spaced samples exactly 1 minute apart. Before Prometheus
3.x, range query with `5m` will mostly return 5 samples. But if the query v3, a range query with `5m` would usually return 5 samples. But if the query
evaluation aligns perfectly with a scrape, it would return 6 samples. In evaluation aligns perfectly with a scrape, it would return 6 samples. In
Prometheus 3.x queries like this will always return 5 samples. Prometheus v3 queries like this will always return 5 samples.
This change has likely few effects for everyday use, except for some sub query This change has likely few effects for everyday use, except for some subquery
use cases. use cases.
Query front-ends that align queries usually align sub-queries to multiples of Query front-ends that align queries usually align subqueries to multiples of
the step size. These sub queries will likely be affected. the step size. These subqueries will likely be affected.
Tests are more likely to affected. To fix those either adjust the expected Tests are more likely to affected. To fix those either adjust the expected
number of samples or extend to range by less then one sample interval. number of samples or extend the range by less than one sample interval.
- The `holt_winters` function has been renamed to `double_exponential_smoothing` - The `holt_winters` function has been renamed to `double_exponential_smoothing`
and is now guarded by the `promql-experimental-functions` feature flag. and is now guarded by the `promql-experimental-functions` feature flag.
If you want to keep using holt_winters, you have to do both of these things: If you want to keep using `holt_winters`, you have to do both of these things:
- Rename holt_winters to double_exponential_smoothing in your queries. - Rename `holt_winters` to `double_exponential_smoothing` in your queries.
- Pass `--enable-feature=promql-experimental-functions` in your Prometheus - Pass `--enable-feature=promql-experimental-functions` in your Prometheus
cli invocation.. CLI invocation.
## Scrape protocols ## Scrape protocols
Prometheus v3 is more strict concerning the Content-Type header received when Prometheus v3 is more strict concerning the Content-Type header received when
@ -105,12 +105,12 @@ may now fail if this fallback protocol is not specified.
### TSDB format and downgrade ### TSDB format and downgrade
The TSDB format has been changed in Prometheus v2.55 in preparation for changes The TSDB format has been changed in Prometheus v2.55 in preparation for changes
to the index format. Consequently a Prometheus v3 tsdb can only be read by a to the index format. Consequently, a Prometheus v3 TSDB can only be read by a
Prometheus v2.55 or newer. Prometheus v2.55 or newer.
Before upgrading to Prometheus v3 please upgrade to v2.55 first and confirm Before upgrading to Prometheus v3 please upgrade to v2.55 first and confirm
Prometheus works as expected. Only then continue with the upgrade to v3. Prometheus works as expected. Only then continue with the upgrade to v3.
### TSDB Storage contract ### TSDB storage contract
TSDB compatible storage is now expected to return results matching the specified TSDB compatible storage is now expected to return results matching the specified
selectors. This might impact some third party implementations, most likely selectors. This might impact some third party implementations, most likely
implementing `remote_read`. implementing `remote_read`.
@ -123,7 +123,7 @@ endpoints. Furthermore, metric and label names that would have previously been
flagged as invalid no longer will be. flagged as invalid no longer will be.
Users wishing to preserve the original validation behavior can update their Users wishing to preserve the original validation behavior can update their
prometheus yaml configuration to specify the legacy validation scheme: Prometheus yaml configuration to specify the legacy validation scheme:
``` ```
global: global:
@ -159,7 +159,7 @@ time=2024-10-24T00:03:07.542+02:00 level=INFO source=/home/user/go/src/github.co
### `le` and `quantile` label values ### `le` and `quantile` label values
In Prometheus v3, the values of the `le` label of classic histograms and the In Prometheus v3, the values of the `le` label of classic histograms and the
`quantile` label of summaries are normalized upon ingestions. In Prometheus v2 `quantile` label of summaries are normalized upon ingestion. In Prometheus v2
the value of these labels depended on the scrape protocol (protobuf vs text the value of these labels depended on the scrape protocol (protobuf vs text
format) in some situations. This led to label values changing based on the format) in some situations. This led to label values changing based on the
scrape protocol. E.g. a metric exposed as `my_classic_hist{le="1"}` would be scrape protocol. E.g. a metric exposed as `my_classic_hist{le="1"}` would be

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