# PromQL extensions

VictoriaMetrics supports [standard PromQL](https://prometheus.io/docs/prometheus/latest/querying/basics/)
including [subqueries](https://prometheus.io/blog/2019/01/28/subquery-support/).
Additionally it supports useful extensions mentioned below.
Try these extensions on [an editable Grafana dashboard](http://play-grafana.victoriametrics.com:3000/d/4ome8yJmz/node-exporter-on-victoriametrics-demo).

- [`WITH` templates](https://play.victoriametrics.com/promql/expand-with-exprs). This feature simplifies writing and managing complex queries. Go to [`WITH` templates playground](https://victoriametrics.com/promql/expand-with-exprs) and try it.
- Metric names and metric labels may contain escaped chars. For instance, `foo\-bar{baz\=aa="b"}` is valid expression. It returns time series with name `foo-bar` containing label `baz=aa` with value `b`. Additionally, `\xXX` escape sequence is supported, where `XX` is hexadecimal representation of escaped char.
- `offset`, range duration and step value for range vector may refer to the current step aka `$__interval` value from Grafana.
  For instance, `rate(metric[10i] offset 5i)` would return per-second rate over a range covering 10 previous steps with the offset of 5 steps.
- `offset` may be put anywere in the query. For instance, `sum(foo) offset 24h`.
- `offset` may be negative. For example, `q offset -1h`.
- `default` binary operator. `q1 default q2` substitutes `NaN` values from `q1` with the corresponding values from `q2`.
- `histogram_quantile` accepts optional third arg - `boundsLabel`. In this case it returns `lower` and `upper` bounds for the estimated percentile. See [this issue for details](https://github.com/prometheus/prometheus/issues/5706).
- `if` binary operator. `q1 if q2` removes values from `q1` for `NaN` values from `q2`.
- `ifnot` binary operator. `q1 ifnot q2` removes values from `q1` for non-`NaN` values from `q2`.
- Trailing commas on all the lists are allowed - label filters, function args and with expressions. For instance, the following queries are valid: `m{foo="bar",}`, `f(a, b,)`, `WITH (x=y,) x`. This simplifies maintenance of multi-line queries.
- String literals may be concatenated. This is useful with `WITH` templates: `WITH (commonPrefix="long_metric_prefix_") {__name__=commonPrefix+"suffix1"} / {__name__=commonPrefix+"suffix2"}`.
- Range duration in functions such as [rate](https://prometheus.io/docs/prometheus/latest/querying/functions/#rate()) may be omitted. VictoriaMetrics automatically selects range duration depending on the current step used for building the graph. For instance, the following query is valid in VictoriaMetrics: `rate(node_network_receive_bytes_total)`.
- [Range duration](https://prometheus.io/docs/prometheus/latest/querying/basics/#range-vector-selectors) and [offset](https://prometheus.io/docs/prometheus/latest/querying/basics/#offset-modifier) may be fractional. For instance, `rate(node_network_receive_bytes_total[1.5m] offset 0.5d)`.
- Comments starting with `#` and ending with newline. For instance, `up # this is a comment for 'up' metric`.
- Rollup functions - `rollup(m[d])`, `rollup_rate(m[d])`, `rollup_deriv(m[d])`, `rollup_increase(m[d])`, `rollup_delta(m[d])` - return `min`, `max` and `avg`
  values for all the `m` data points over `d` duration.
- `rollup_candlestick(m[d])` - returns `open`, `close`, `low` and `high` values (OHLC) for all the `m` data points over `d` duration. This function is useful for financial applications.
- `union(q1, ... qN)` function for building multiple graphs for `q1`, ... `qN` subqueries with a single query. The `union` function name may be skipped -
  the following queries are equivalent: `union(q1, q2)` and `(q1, q2)`.
- `ru(freeResources, maxResources)` function for returning resource utilization percentage in the range `0% - 100%`. For instance, `ru(node_memory_MemFree_bytes, node_memory_MemTotal_bytes)` returns memory utilization over [node_exporter](https://github.com/prometheus/node_exporter) metrics.
- `ttf(slowlyChangingFreeResources)` function for returning the time in seconds when the given `slowlyChangingFreeResources` expression reaches zero. For instance, `ttf(node_filesystem_avail_byte)` returns the time to storage space exhaustion. This function may be useful for capacity planning.
- Functions for label manipulation:
  - `alias(q, name)` for setting metric name across all the time series `q`.
  - `label_set(q, label1, value1, ... labelN, valueN)` for setting the given values for the given labels on `q`.
  - `label_del(q, label1, ... labelN)` for deleting the given labels from `q`.
  - `label_keep(q, label1, ... labelN)` for deleting all the labels except the given labels from `q`.
  - `label_copy(q, src_label1, dst_label1, ... src_labelN, dst_labelN)` for copying label values from `src_*` to `dst_*`.
  - `label_move(q, src_label1, dst_label1, ... src_labelN, dst_labelN)` for moving label values from `src_*` to `dst_*`.
  - `label_transform(q, label, regexp, replacement)` for replacing all the `regexp` occurences with `replacement` in the `label` values from `q`.
  - `label_value(q, label)` - returns numeric values for the given `label` from `q`.
- `step()` function for returning the step in seconds used in the query.
- `start()` and `end()` functions for returning the start and end timestamps of the `[start ... end]` range used in the query.
- `integrate(m[d])` for returning integral over the given duration `d` for the given metric `m`.
- `ideriv(m)` - for calculating `instant` derivative for `m`.
- `deriv_fast(m[d])` - for calculating `fast` derivative for `m` based on the first and the last points from duration `d`.
- `running_` functions - `running_sum`, `running_min`, `running_max`, `running_avg` - for calculating [running values](https://en.wikipedia.org/wiki/Running_total) on the selected time range.
- `range_` functions - `range_sum`, `range_min`, `range_max`, `range_avg`, `range_first`, `range_last`, `range_median`, `range_quantile` - for calculating global value over the selected time range.
- `smooth_exponential(q, sf)` - smooths `q` using [exponential moving average](https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average) with the given smooth factor `sf`.
- `remove_resets(q)` - removes counter resets from `q`.
- `lag(q[d])` - returns lag between the current timestamp and the timestamp from the previous data point in `q` over `d`.
- `lifetime(q[d])` - returns lifetime of `q` over `d` in seconds. It is expected that `d` exceeds the lifetime of `q`.
- `scrape_interval(q[d])` - returns the average interval in seconds between data points of `q` over `d` aka `scrape interval`.
- Trigonometric functions - `sin(q)`, `cos(q)`, `asin(q)`, `acos(q)` and `pi()`.
- `median_over_time(m[d])` - calculates median values for `m` over `d` time window. Shorthand to `quantile_over_time(0.5, m[d])`.
- `median(q)` - median aggregate. Shorthand to `quantile(0.5, q)`.
- `limitk(k, q)` - limits the number of time series returned from `q` to `k`.
- `keep_last_value(q)` - fills missing data (gaps) in `q` with the previous value.
- `distinct_over_time(m[d])` - returns distinct number of values for `m` data points over `d` duration.
- `distinct(q)` - returns a time series with the number of unique values for each timestamp in `q`.
- `sum2_over_time(m[d])` - returns sum of squares for all the `m` values over `d` duration.
- `sum2(q)` - returns a time series with sum of square values for each timestamp in `q`.
- `geomean_over_time(m[d])` - returns [geomean](https://en.wikipedia.org/wiki/Geometric_mean) value for all the `m` value over `d` duration.
- `geomean(q)` - returns a time series with [geomean](https://en.wikipedia.org/wiki/Geometric_mean) value for each timestamp in `q`.
- `rand()`, `rand_normal()` and `rand_exponential()` functions - for generating pseudo-random series with even, normal and exponential distribution.
- `increases_over_time(m[d])` and `decreases_over_time(m[d])` - returns the number of `m` increases or decreases over the given duration `d`.
- `prometheus_buckets(q)` - converts [VictoriaMetrics histogram](https://godoc.org/github.com/VictoriaMetrics/metrics#Histogram) buckets to Prometheus buckets with `le` labels.
- `histogram(q)` - calculates aggregate histogram over `q` time series for each point on the graph. See [this article](https://medium.com/@valyala/improving-histogram-usability-for-prometheus-and-grafana-bc7e5df0e350) for more details.
- `topk_*` and `bottomk_*` aggregate functions, which return up to K time series. Note that the standard `topk` function may return more than K time series -
   see [this article](https://www.robustperception.io/graph-top-n-time-series-in-grafana) for details.
   - `topk_min(k, q)` - returns top K time series with the max minimums on the given time range
   - `topk_max(k, q)` - returns top K time series with the max maximums on the given time range
   - `topk_avg(k, q)` - returns top K time series with the max averages on the given time range
   - `topk_median(k, q)` - returns top K time series with the max medians on the given time range
   - `bottomk_min(k, q)` - returns bottom K time series with the min minimums on the given time range
   - `bottomk_max(k, q)` - returns bottom K time series with the min maximums on the given time range
   - `bottomk_avg(k, q)` - returns bottom K time series with the min averages on the given time range
   - `bottomk_median(k, q)` - returns bottom K time series with the min medians on the given time range