update wiki pages

CHANGELOG.md

@@ -14,6 +14,23 @@ The following tip changes can be tested by building VictoriaMetrics components f
 
 ## tip
 
+* FEATURE: add support for conditional relabeling via `if` filter. The `if` filter can contain arbitrary [series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors). For example, the following rule drops targets matching `foo{bar="baz"}` series selector:
+
+```yml
+- action: drop
+  if: 'foo{bar="baz"}'
+```
+
+This rule is equivalent to less clear traditional one:
+
+```yml
+- action: drop
+  source_labels: [__name__, bar]
+  regex: 'foo;baz'
+```
+
+  See [relabeling docs](https://docs.victoriametrics.com/vmagent.html#relabeling) and [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1998) for more details.
+
 * FEATURE: reduce memory usage for various caches under [high churn rate](https://docs.victoriametrics.com/FAQ.html#what-is-high-churn-rate).
 
 * BUGFIX: [vmgateway](https://docs.victoriametrics.com/vmgateway.html): properly parse JWT tokens if they are encoded with [URL-safe base64 encoding](https://datatracker.ietf.org/doc/html/rfc4648#section-5).

vmagent.md

@@ -268,7 +268,7 @@ Labels can be added to metrics by the following mechanisms:
 
 ## Relabeling
 
-`vmagent` and VictoriaMetrics support Prometheus-compatible relabeling.
+VictoriaMetrics components (including `vmagent`) support Prometheus-compatible relabeling.
 They provide the following additional actions on top of actions from the [Prometheus relabeling](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config):
 
 * `replace_all`: replaces all of the occurences of `regex` in the values of `source_labels` with the `replacement` and stores the results in the `target_label`.
@@ -293,6 +293,21 @@ The `regex` value can be split into multiple lines for improved readability and
   - "foo_.+"
 ```
 
+VictoriaMetrics components support an optional `if` filter, which can be used for conditional relabeling. The `if` filter may contain arbitrary [time series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors). For example, the following relabeling rule drops targets, which don't match `foo{bar="baz"}` series selector:
+
+```yaml
+- action: keep
+  if: 'foo{bar="baz"}'
+```
+
+This is equivalent to less clear traditional relabeling rule:
+
+```yaml
+- action: keep
+  source_labels: [__name__, bar]
+  regex: 'foo;baz'
+```
+
 The relabeling can be defined in the following places:
 
 * At the `scrape_config -> relabel_configs` section in `-promscrape.config` file. This relabeling is applied to target labels. This relabeling can be debugged by passing `relabel_debug: true` option to the corresponding `scrape_config` section. In this case `vmagent` logs target labels before and after the relabeling and then drops the logged target.