VictoriaMetrics/docs/stream-aggregation.md

---
sort: 98
weight: 98
title: Streaming aggregation
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  docs:
    parent: "victoriametrics"
    weight: 98
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---

# Streaming aggregation

[vmagent](https://docs.victoriametrics.com/vmagent.html) and [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html)
can aggregate incoming [samples](https://docs.victoriametrics.com/keyConcepts.html#raw-samples) in streaming mode by time and by labels before data is written to remote storage.
The aggregation is applied to all the metrics received via any [supported data ingestion protocol](https://docs.victoriametrics.com/#how-to-import-time-series-data)
and/or scraped from [Prometheus-compatible targets](https://docs.victoriametrics.com/#how-to-scrape-prometheus-exporters-such-as-node-exporter).

Stream aggregation ignores timestamps associated with the input [samples](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).
It expects that the ingested samples have timestamps close to the current time.

Stream aggregation is configured via the following command-line flags:

- `-remoteWrite.streamAggr.config` at [vmagent](https://docs.victoriametrics.com/vmagent.html).
  This flag can be specified individually per each `-remoteWrite.url`.
  This allows writing different aggregates to different remote storage destinations.
- `-streamAggr.config` at [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html).

These flags must point to a file containing [stream aggregation config](#stream-aggregation-config).

By default, the following data is written to the storage when stream aggregation is enabled:

- the aggregated samples;
- the raw input samples, which didn't match any `match` option in the provided [config](#stream-aggregation-config).

This behaviour can be changed via the following command-line flags:

- `-remoteWrite.streamAggr.keepInput` at [vmagent](https://docs.victoriametrics.com/vmagent.html) and `-streamAggr.keepInput`
  at [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html).
  If one of these flags are set, then all the input samples are written to the storage alongside the aggregated samples.
  The `-remoteWrite.streamAggr.keepInput` flag can be specified individually per each `-remoteWrite.url`.
- `-remoteWrite.streamAggr.dropInput` at [vmagent](https://docs.victoriametrics.com/vmagent.html) and `-streamAggr.dropInput`
  at [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html).
  If one of these flags are set, then all the input samples are dropped, while only the aggregated samples are written to the storage.
  The `-remoteWrite.streamAggr.dropInput` flag can be specified individually per each `-remoteWrite.url`.

By default, all the input samples are aggregated. Sometimes it is needed to de-duplicate samples before the aggregation.
For example, if the samples are received from replicated sources.
The following command-line flag can be used for enabling the [de-duplication](https://docs.victoriametrics.com/#deduplication)
before aggregation in this case:

- `-remoteWrite.streamAggr.dedupInterval` at [vmagent](https://docs.victoriametrics.com/vmagent.html).
  This flag can be specified individually per each `-remoteWrite.url`.
  This allows setting different de-duplication intervals per each configured remote storage.
- `-streamAggr.dedupInterval` at [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html).

## Use cases

Stream aggregation can be used in the following cases:

* [Statsd alternative](#statsd-alternative)
* [Recording rules alternative](#recording-rules-alternative)
* [Reducing the number of stored samples](#reducing-the-number-of-stored-samples)
* [Reducing the number of stored series](#reducing-the-number-of-stored-series)

### Statsd alternative

Stream aggregation can be used as [statsd](https://github.com/statsd/statsd) alternative in the following cases:

* [Counting input samples](#counting-input-samples)
* [Summing input metrics](#summing-input-metrics)
* [Quantiles over input metrics](#quantiles-over-input-metrics)
* [Histograms over input metrics](#histograms-over-input-metrics)
* [Aggregating histograms](#aggregating-histograms)

Currently, streaming aggregation is available only for [supported data ingestion protocols](https://docs.victoriametrics.com/#how-to-import-time-series-data)
and not available for [Statsd metrics format](https://github.com/statsd/statsd/blob/master/docs/metric_types.md).

### Recording rules alternative

Sometimes [alerting queries](https://docs.victoriametrics.com/vmalert.html#alerting-rules) may require non-trivial amounts of CPU, RAM,
disk IO and network bandwidth at metrics storage side. For example, if `http_request_duration_seconds` histogram is generated by thousands
of application instances, then the alerting query `histogram_quantile(0.99, sum(increase(http_request_duration_seconds_bucket[5m])) without (instance)) > 0.5`
can become slow, since it needs to scan too big number of unique [time series](https://docs.victoriametrics.com/keyConcepts.html#time-series)
with `http_request_duration_seconds_bucket` name. This alerting query can be speed up by pre-calculating
the `sum(increase(http_request_duration_seconds_bucket[5m])) without (instance)` via [recording rule](https://docs.victoriametrics.com/vmalert.html#recording-rules).
But this recording rule may take too much time to execute too. In this case the slow recording rule can be substituted
with the following [stream aggregation config](#stream-aggregation-config):

```yaml
- match: 'http_request_duration_seconds_bucket'
  interval: 5m
  without: [instance]
  outputs: [total]
```

This stream aggregation generates `http_request_duration_seconds_bucket:5m_without_instance_total` output series according to [output metric naming](#output-metric-names).
Then these series can be used in [alerting rules](https://docs.victoriametrics.com/vmalert.html#alerting-rules):

```metricsql
histogram_quantile(0.99, last_over_time(http_request_duration_seconds_bucket:5m_without_instance_total[5m])) > 0.5
```

This query is executed much faster than the original query, because it needs to scan much lower number of time series.

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [aggregating by labels](#aggregating-by-labels).

Field `interval` is recommended to be set to a value at least several times higher than your metrics collect interval.


### Reducing the number of stored samples

If per-[series](https://docs.victoriametrics.com/keyConcepts.html#time-series) samples are ingested at high frequency,
then this may result in high disk space usage, since too much data must be stored to disk. This also may result
in slow queries, since too much data must be processed during queries.

This can be fixed with the stream aggregation by increasing the interval between per-series samples stored in the database.

For example, the following [stream aggregation config](#stream-aggregation-config) reduces the frequency of input samples
to one sample per 5 minutes per each input time series (this operation is also known as downsampling):

```yaml
  # Aggregate metrics ending with _total with `total` output.
  # See https://docs.victoriametrics.com/stream-aggregation.html#aggregation-outputs
- match: '{__name__=~".+_total"}'
  interval: 5m
  outputs: [total]

  # Downsample other metrics with `count_samples`, `sum_samples`, `min` and `max` outputs
  # See https://docs.victoriametrics.com/stream-aggregation.html#aggregation-outputs
- match: '{__name__!~".+_total"}'
  interval: 5m
  outputs: [count_samples, sum_samples, min, max]
```

The aggregated output metrics have the following names according to [output metric naming](#output-metric-names):

```
# For input metrics ending with _total
some_metric_total:5m_total

# For input metrics not ending with _total
some_metric:5m_count_samples
some_metric:5m_sum_samples
some_metric:5m_min
some_metric:5m_max
```

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [aggregating histograms](#aggregating-histograms) and [aggregating by labels](#aggregating-by-labels).

### Reducing the number of stored series

Sometimes applications may generate too many [time series](https://docs.victoriametrics.com/keyConcepts.html#time-series).
For example, the `http_requests_total` metric may have `path` or `user` label with too big number of unique values.
In this case the following stream aggregation can be used for reducing the number metrics stored in VictoriaMetrics:

```yaml
- match: 'http_requests_total'
  interval: 30s
  without: [path, user]
  outputs: [total]
```

This config specifies labels, which must be removed from the aggregate output, in the `without` list.
See [these docs](#aggregating-by-labels) for more details.

The aggregated output metric has the following name according to [output metric naming](#output-metric-names):

```
http_requests_total:30s_without_path_user_total
```

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [aggregating histograms](#aggregating-histograms).

### Counting input samples

If the monitored application generates event-based metrics, then it may be useful to count the number of such metrics
at stream aggregation level.

For example, if an advertising server generates `hits{some="labels"} 1` and `clicks{some="labels"} 1` metrics
per each incoming hit and click, then the following [stream aggregation config](#stream-aggregation-config)
can be used for counting these metrics per every 30 second interval:

```yml
- match: '{__name__=~"hits|clicks"}'
  interval: 30s
  outputs: [count_samples]
```

This config generates the following output metrics for `hits` and `clicks` input metrics
according to [output metric naming](#output-metric-names):

```
hits:30s_count_samples count1
clicks:30s_count_samples count2
```

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [aggregating by labels](#aggregating-by-labels).


### Summing input metrics

If the monitored application calculates some events and then sends the calculated number of events to VictoriaMetrics
at irregular intervals or at too high frequency, then stream aggregation can be used for summing such events
and writing the aggregate sums to the storage at regular intervals.

For example, if an advertising server generates `hits{some="labels} N` and `clicks{some="labels"} M` metrics
at irregular intervals, then the following [stream aggregation config](#stream-aggregation-config)
can be used for summing these metrics per every minute:

```yml
- match: '{__name__=~"hits|clicks"}'
  interval: 1m
  outputs: [sum_samples]
```

This config generates the following output metrics according to [output metric naming](#output-metric-names):

```
hits:1m_sum_samples sum1
clicks:1m_sum_samples sum2
```

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [aggregating by labels](#aggregating-by-labels).


### Quantiles over input metrics

If the monitored application generates measurement metrics per each request, then it may be useful to calculate
the pre-defined set of [percentiles](https://en.wikipedia.org/wiki/Percentile) over these measurements.

For example, if the monitored application generates `request_duration_seconds N` and `response_size_bytes M` metrics
per each incoming request, then the following [stream aggregation config](#stream-aggregation-config)
can be used for calculating 50th and 99th percentiles for these metrics every 30 seconds:

```yaml
- match:
  - request_duration_seconds
  - response_size_bytes
  interval: 30s
  outputs: ["quantiles(0.50, 0.99)"]
```

This config generates the following output metrics according to [output metric naming](#output-metric-names):

```
request_duration_seconds:30s_quantiles{quantile="0.50"} value1
request_duration_seconds:30s_quantiles{quantile="0.99"} value2

response_size_bytes:30s_quantiles{quantile="0.50"} value1
response_size_bytes:30s_quantiles{quantile="0.99"} value2
```

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [histograms over input metrics](#histograms-over-input-metrics) and [aggregating by labels](#aggregating-by-labels).

### Histograms over input metrics

If the monitored application generates measurement metrics per each request, then it may be useful to calculate
a [histogram](https://docs.victoriametrics.com/keyConcepts.html#histogram) over these metrics.

For example, if the monitored application generates `request_duration_seconds N` and `response_size_bytes M` metrics
per each incoming request, then the following [stream aggregation config](#stream-aggregation-config)
can be used for calculating [VictoriaMetrics histogram buckets](https://valyala.medium.com/improving-histogram-usability-for-prometheus-and-grafana-bc7e5df0e350)
for these metrics every 60 seconds:

```yaml
- match:
  - request_duration_seconds
  - response_size_bytes
  interval: 60s
  outputs: [histogram_bucket]
```

This config generates the following output metrics according to [output metric naming](#output-metric-names).

```
request_duration_seconds:60s_histogram_bucket{vmrange="start1...end1"} count1
request_duration_seconds:60s_histogram_bucket{vmrange="start2...end2"} count2
...
request_duration_seconds:60s_histogram_bucket{vmrange="startN...endN"} countN

response_size_bytes:60s_histogram_bucket{vmrange="start1...end1"} count1
response_size_bytes:60s_histogram_bucket{vmrange="start2...end2"} count2
...
response_size_bytes:60s_histogram_bucket{vmrange="startN...endN"} countN
```

The resulting histogram buckets can be queried with [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html) in the following ways:

1. An estimated 50th and 99th [percentiles](https://en.wikipedia.org/wiki/Percentile) of the request duration over the last hour:

   ```metricsql
   histogram_quantiles("quantile", 0.50, 0.99, sum(increase(request_duration_seconds:60s_histogram_bucket[1h])) by (vmrange))
   ```

   This query uses [histogram_quantiles](https://docs.victoriametrics.com/MetricsQL.html#histogram_quantiles) function.

1. An estimated [standard deviation](https://en.wikipedia.org/wiki/Standard_deviation) of the request duration over the last hour:

   ```metricsql
   histogram_stddev(sum(increase(request_duration_seconds:60s_histogram_bucket[1h])) by (vmrange))
   ```

   This query uses [histogram_stddev](https://docs.victoriametrics.com/MetricsQL.html#histogram_stddev) function.

1. An estimated share of requests with the duration smaller than `0.5s` over the last hour:

   ```metricsql
   histogram_share(0.5, sum(increase(request_duration_seconds:60s_histogram_bucket[1h])) by (vmrange))
   ```

   This query uses [histogram_share](https://docs.victoriametrics.com/MetricsQL.html#histogram_share) function.

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [quantiles over input metrics](#quantiles-over-input-metrics) and [aggregating by labels](#aggregating-by-labels).

### Aggregating histograms

[Histogram](https://docs.victoriametrics.com/keyConcepts.html#histogram) is a set of [counter](https://docs.victoriametrics.com/keyConcepts.html#counter)
metrics with different `vmrange` or `le` labels. As they're counters, the applicable aggregation output is 
[total](https://docs.victoriametrics.com/stream-aggregation.html#total):
```yaml
- match: 'http_request_duration_seconds_bucket'
  interval: 1m
  without: [instance]
  outputs: [total]
  output_relabel_configs:
    - source_labels: [__name__]
      target_label: __name__
```

This config generates the following output metrics according to [output metric naming](#output-metric-names):
```
http_request_duration_seconds_bucket:1m_without_instance_total{le="0.1"} value1
http_request_duration_seconds_bucket:1m_without_instance_total{le="0.2"} value2
http_request_duration_seconds_bucket:1m_without_instance_total{le="0.4"} value3
http_request_duration_seconds_bucket:1m_without_instance_total{le="1"}   value4
http_request_duration_seconds_bucket:1m_without_instance_total{le="3"}   value5
http_request_duration_seconds_bucket:1m_without_instance_total{le="8"}   value6
http_request_duration_seconds_bucket:1m_without_instance_total{le="20"}  value7
http_request_duration_seconds_bucket:1m_without_instance_total{le="60"}  value8
http_request_duration_seconds_bucket:1m_without_instance_total{le="120"} value9
http_request_duration_seconds_bucket:1m_without_instance_total{le="+Inf" value10
```

The resulting metrics can be used in [histogram_quantile](https://docs.victoriametrics.com/MetricsQL.html#histogram_quantile)
function:
```metricsql
histogram_quantile(0.9, sum(rate(http_request_duration_seconds_bucket:1m_without_instance_total[5m])) by(le))
```

Please note, histograms can be aggregated if their `le` labels are configured identically. 
[VictoriaMetrics histogram buckets](https://valyala.medium.com/improving-histogram-usability-for-prometheus-and-grafana-bc7e5df0e350)
have no such requirement.

See [the list of aggregate output](#aggregation-outputs), which can be specified at `output` field.
See also [histograms over input metrics](#histograms-over-input-metrics) and [quantiles over input metrics](#quantiles-over-input-metrics).


## Output metric names

Output metric names for stream aggregation are constructed according to the following pattern:

```
<metric_name>:<interval>[_by_<by_labels>][_without_<without_labels>]_<output>
```

- `<metric_name>` is the original metric name.
- `<interval>` is the interval specified in the [stream aggregation config](#stream-aggregation-config).
- `<by_labels>` is `_`-delimited sorted list of `by` labels specified in the [stream aggregation config](#stream-aggregation-config).
  If the `by` list is missing in the config, then the `_by_<by_labels>` part isn't included in the output metric name.
- `<without_labels>` is an optional `_`-delimited sorted list of `without` labels specified in the [stream aggregation config](#stream-aggregation-config).
  If the `without` list is missing in the config, then the `_without_<without_labels>` part isn't included in the output metric name.
- `<output>` is the aggregate used for constructing the output metric. The aggregate name is taken from the `outputs` list
  at the corresponding [stream aggregation config](#stream-aggregation-config).

Both input and output metric names can be modified if needed via relabeling according to [these docs](#relabeling).


## Relabeling

It is possible to apply [arbitrary relabeling](https://docs.victoriametrics.com/vmagent.html#relabeling) to input and output metrics
during stream aggregation via `input_relabel_configs` and `output_relabel_config` options in [stream aggregation config](#stream-aggregation-config).

For example, the following config removes the `:1m_sum_samples` suffix added [to the output metric name](#output-metric-names):

```yml
- interval: 1m
  outputs: [sum_samples]
  output_relabel_configs:
  - source_labels: [__name__]
    target_label: __name__
    regex: "(.+):.+"
```

## Aggregation outputs

The aggregations are calculated during the `interval` specified in the [config](#stream-aggregation-config)
and then sent to the storage.

If `by` and `without` lists are specified in the [config](#stream-aggregation-config),
then the [aggregation by labels](#aggregating-by-labels) is performed additionally to aggregation by `interval`.

Below are aggregation functions that can be put in the `outputs` list at [stream aggregation config](#stream-aggregation-config).

### total

`total` generates output [counter](https://docs.victoriametrics.com/keyConcepts.html#counter) by summing the input counters.
`total` only makes sense for aggregating [counter](https://docs.victoriametrics.com/keyConcepts.html#counter) metrics.

The results of `total` is equal to the `sum(some_counter)` query.

For example, see below time series produced by config with aggregation interval `1m` and `by: ["instance"]` and  the regular query:

<img alt="total aggregation" src="stream-aggregation-check-total.png">

`total` is not affected by [counter resets](https://docs.victoriametrics.com/keyConcepts.html#counter) - 
it continues to increase monotonically with respect to the previous value.
The counters are most often reset when the application is restarted.

For example: 

<img alt="total aggregation counter reset" src="stream-aggregation-check-total-reset.png">

The same behavior will occur when creating or deleting new series in an aggregation group -
`total` will increase monotonically considering the values of the series set.  
An example of changing a set of series can be restarting a pod in the Kubernetes.
This changes a label with pod's name in the series, but `total` account for such a scenario and do not reset the state of aggregated metric.

Aggregating irregular and sporadic metrics (received from [Lambdas](https://aws.amazon.com/lambda/)
or [Cloud Functions](https://cloud.google.com/functions)) can be controlled via [staleness_inteval](#stream-aggregation-config).

### increase

`increase` returns the increase of input [counters](https://docs.victoriametrics.com/keyConcepts.html#counter).
`increase` only makes sense for aggregating [counter](https://docs.victoriametrics.com/keyConcepts.html#counter) metrics.

The results of `increase` with aggregation interval of `1m` is equal to the `increase(some_counter[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and `by: ["instance"]` and  the regular query:

<img alt="increase aggregation" src="stream-aggregation-check-increase.png">

Aggregating irregular and sporadic metrics (received from [Lambdas](https://aws.amazon.com/lambda/)
or [Cloud Functions](https://cloud.google.com/functions)) can be controlled via [staleness_inteval](#stream-aggregation-config).

### count_series

`count_series` counts the number of unique [time series](https://docs.victoriametrics.com/keyConcepts.html#time-series).

The results of `count_series` is equal to the `count(some_metric)` query.

### count_samples

`count_samples` counts the number of input [samples](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).

The results of `count_samples` with aggregation interval of `1m` is equal to the `count_over_time(some_metric[1m])` query.

### sum_samples

`sum_samples` sums input [sample values](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).
`sum_samples` makes sense only for aggregating [gauge](https://docs.victoriametrics.com/keyConcepts.html#gauge) metrics.

The results of `sum_samples` with aggregation interval of `1m` is equal to the `sum_over_time(some_metric[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and the regular query:

<img alt="sum_samples aggregation" src="stream-aggregation-check-sum-samples.png">

### last

`last` returns the last input [sample value](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).

The results of `last` with aggregation interval of `1m` is equal to the `last_over_time(some_metric[1m])` query.

This aggregation output doesn't make much sense with `by` lists specified in the [config](#stream-aggregation-config). 
The result of aggregation by labels in this case will be undetermined, because it depends on the order of processing the time series.

### min

`min` returns the minimum input [sample value](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).

The results of `min` with aggregation interval of `1m` is equal to the `min_over_time(some_metric[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and the regular query:

<img alt="min aggregation" src="stream-aggregation-check-min.png">

### max

`max` returns the maximum input [sample value](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).

The results of `max` with aggregation interval of `1m` is equal to the `max_over_time(some_metric[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and the regular query:

<img alt="total aggregation" src="stream-aggregation-check-max.png">

### avg

`avg` returns the average input [sample value](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).

The results of `avg` with aggregation interval of `1m` is equal to the `avg_over_time(some_metric[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and `by: ["instance"]` and  the regular query:

<img alt="avg aggregation" src="stream-aggregation-check-avg.png">

### stddev

`stddev` returns [standard deviation](https://en.wikipedia.org/wiki/Standard_deviation) for the input [sample values](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).
`stddev` makes sense only for aggregating [gauge](https://docs.victoriametrics.com/keyConcepts.html#gauge) metrics.

The results of `stddev` with aggregation interval of `1m` is equal to the `stddev_over_time(some_metric[1m])` query.

### stdvar

`stdvar` returns [standard variance](https://en.wikipedia.org/wiki/Variance) for the input [sample values](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).
`stdvar` makes sense only for aggregating [gauge](https://docs.victoriametrics.com/keyConcepts.html#gauge) metrics.

The results of `stdvar` with aggregation interval of `1m` is equal to the `stdvar_over_time(some_metric[1m])` query.

For example, see below time series produced by config with aggregation interval `1m` and the regular query:

<img alt="stdvar aggregation" src="stream-aggregation-check-stdvar.png">

### histogram_bucket

`histogram_bucket` returns [VictoriaMetrics histogram buckets](https://valyala.medium.com/improving-histogram-usability-for-prometheus-and-grafana-bc7e5df0e350)
  for the input [sample values](https://docs.victoriametrics.com/keyConcepts.html#raw-samples).
`histogram_bucket` makes sense only for aggregating [gauge](https://docs.victoriametrics.com/keyConcepts.html#gauge) metrics.
See how to aggregate regular histograms [here](#aggregating-histograms).

The results of `histogram_bucket` with aggregation interval of `1m` is equal to the `histogram_over_time(some_histogram_bucket[1m])` query.

Aggregating irregular and sporadic metrics (received from [Lambdas](https://aws.amazon.com/lambda/)
or [Cloud Functions](https://cloud.google.com/functions)) can be controlled via [staleness_inteval](#stream-aggregation-config).

### quantiles

`quantiles(phi1, ..., phiN)` returns [percentiles](https://en.wikipedia.org/wiki/Percentile) for the given `phi*`
over the input [sample values](https://docs.victoriametrics.com/keyConcepts.html#raw-samples). 
The `phi` must be in the range `[0..1]`, where `0` means `0th` percentile, while `1` means `100th` percentile.
`quantiles(...)` makes sense only for aggregating [gauge](https://docs.victoriametrics.com/keyConcepts.html#gauge) metrics.

The results of `quantiles(phi1, ..., phiN)` with aggregation interval of `1m` 
is equal to the `quantiles_over_time("quantile", phi1, ..., phiN, some_histogram_bucket[1m])` query.

## Aggregating by labels

All the labels for the input metrics are preserved by default in the output metrics. For example,
the input metric `foo{app="bar",instance="host1"}` results to the output metric `foo:1m_sum_samples{app="bar",instance="host1"}`
when the following [stream aggregation config](#stream-aggregation-config) is used:

```yaml
- interval: 1m
  outputs: [sum_samples]
```

The input labels can be removed via `without` list specified in the config. For example, the following config
removes the `instance` label from output metrics by summing input samples across all the instances:

```yaml
- interval: 1m
  without: [instance]
  outputs: [sum_samples]
```

In this case the `foo{app="bar",instance="..."}` input metrics are transformed into `foo:1m_without_instance_sum_samples{app="bar"}`
output metric according to [output metric naming](#output-metric-names).

It is possible specifying the exact list of labels in the output metrics via `by` list.
For example, the following config sums input samples by the `app` label:

```yaml
- interval: 1m
  by: [app]
  outputs: [sum_samples]
```

In this case the `foo{app="bar",instance="..."}` input metrics are transformed into `foo:1m_by_app_sum_samples{app="bar"}`
output metric according to [output metric naming](#output-metric-names).

The labels used in `by` and `without` lists can be modified via `input_relabel_configs` section - see [these docs](#relabeling).

See also [aggregation outputs](#aggregation-outputs).


## Stream aggregation config

Below is the format for stream aggregation config file, which may be referred via `-remoteWrite.streamAggr.config` command-line flag
at [vmagent](https://docs.victoriametrics.com/vmagent.html) or via `-streamAggr.config` command-line flag
at [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html):

```yaml
  # match is an optional filter for incoming samples to aggregate.
  # It can contain arbitrary Prometheus series selector
  # according to https://docs.victoriametrics.com/keyConcepts.html#filtering .
  # If match isn't set, then all the incoming samples are aggregated.
  #
  # match also can contain a list of series selectors. Then the incoming samples are aggregated
  # if they match at least a single series selector.
  #
- match: 'http_request_duration_seconds_bucket{env=~"prod|staging"}'

  # interval is the interval for the aggregation.
  # The aggregated stats is sent to remote storage once per interval.
  #
  interval: 1m

  # staleness_interval defines an interval after which the series state will be reset if no samples have been sent during it.
  # It means that:
  # - no data point will be written for a resulting time series if it didn't receive any updates during configured interval,
  # - if the series receives updates after the configured interval again, then the time series will be calculated from the initial state
  #   (it's like this series didn't exist until now).
  # Increase this parameter if it is expected for matched metrics to be delayed or collected with irregular intervals exceeding the `interval` value.
  # By default, is equal to x2 of the `interval` field.
  # The parameter is only relevant for outputs: total, increase and histogram_bucket.
  #
  # staleness_interval: 2m

  # without is an optional list of labels, which must be removed from the output aggregation.
  # See https://docs.victoriametrics.com/stream-aggregation.html#aggregating-by-labels
  #
  without: [instance]

  # by is an optional list of labels, which must be preserved in the output aggregation.
  # See https://docs.victoriametrics.com/stream-aggregation.html#aggregating-by-labels
  #
  # by: [job, vmrange]

  # outputs is the list of aggregations to perform on the input data.
  # See https://docs.victoriametrics.com/stream-aggregation.html#aggregation-outputs
  #
  outputs: [total]

  # input_relabel_configs is an optional relabeling rules,
  # which are applied to the incoming samples after they pass the match filter
  # and before being aggregated.
  # See https://docs.victoriametrics.com/stream-aggregation.html#relabeling
  #
  input_relabel_configs:
  - target_label: vmaggr
    replacement: before

  # output_relabel_configs is an optional relabeling rules,
  # which are applied to the aggregated output metrics.
  #
  output_relabel_configs:
  - target_label: vmaggr
    replacement: after
```

The file can contain multiple aggregation configs. The aggregation is performed independently
per each specified config entry.

### Configuration update

[vmagent](https://docs.victoriametrics.com/vmagent.html) and [single-node VictoriaMetrics](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html)
support the following approaches for hot reloading stream aggregation configs from `-remoteWrite.streamAggr.config` and `-streamAggr.config`:

* By sending `SIGHUP` signal to `vmagent` or `victoria-metrics` process:

  ```console
  kill -SIGHUP `pidof vmagent`
  ```

* By sending HTTP request to `/-/reload` endpoint (e.g. `http://vmagent:8429/-/reload` or `http://victoria-metrics:8428/-/reload).

## Cluster mode

If you use [vmagent in cluster mode](https://docs.victoriametrics.com/vmagent.html#scraping-big-number-of-targets) for streaming aggregation
(with `-promscrape.cluster.*` parameters or with `VMAgent.spec.shardCount > 1` for [vmoperator](https://docs.victoriametrics.com/operator))
then be careful when aggregating metrics via `by`, `without` or modifying via `*_relabel_configs` parameters, since incorrect usage
may result in duplicates and data collision. For example, if more than one `vmagent` instance calculates `increase` for metric `http_requests_total`
with `by: [path]` directive, then all the `vmagent` instances will aggregate samples to the same set of time series with different `path` labels.
The proper fix would be to add an unique [`-remoteWrite.label`](https://docs.victoriametrics.com/vmagent.html#adding-labels-to-metrics) per each `vmagent`,
so every `vmagent` aggregates data into distinct set of time series. These time series then can be aggregated later as needed during querying.

For example, if `vmagent` instances run in Docker or Kubernetes, then you can refer `POD_NAME` or `HOSTNAME` environment variables
as an unique label value per each `vmagent`: `-remoteWrite.label='vmagent=%{HOSTNAME}` . See [these docs](https://docs.victoriametrics.com/#environment-variables)
on how to refer environment variables in VictoriaMetrics components.