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docs: renaming: PromQL extensions -> MetricsQL

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# PromQL extensions
# MetricsQL
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).
VictoriaMetrics implements MetricsQL - query language inspired by [PromQL](https://prometheus.io/docs/prometheus/latest/querying/basics/).
It is backwards compatible with PromQL, so Grafana dashboards backed by Prometheus datasource should work the same after switching from Prometheus to VictoriaMetrics.
The following functionality is implemented differently in MetricsQL comparing to PromQL in order to improve user experience:
* MetricsQL takes into account the previous point before the window in square brackets for range functions such as `rate` and `increase`.
It also doesn't extrapolate range function results. This addresses [this issue from Prometheus](https://github.com/prometheus/prometheus/issues/3746).
* MetricsQL returns the expected non-empty responses for requests with `step` values smaller than scrape interval. This addresses [this issue from Grafana](https://github.com/grafana/grafana/issues/11451).
* MetricsQL treats `scalar` type the same as `instant vector` without labels, since users usually don't feel the difference between these types.
See [the corresponding Prometheus docs](https://prometheus.io/docs/prometheus/latest/querying/basics/#expression-language-data-types) for details.
Other PromQL functionality should work the same in MetricsQL. [File an issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues)
if you notice discrepancies between PromQL and MetricsQL results other than mentioned above.
MetricsQL provides additional functionality mentioned below, which is aimed towards solving practical cases.
Feel free [filing a feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues) if you think MetricsQL misses certain useful functionality.
*Note that the functionality mentioned below doesn't work in PromQL, so it is impossible switching back to Prometheus after you start using it.*
This functionality can be tried at [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.

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* [Quick start](Quick-Start)
* [`WITH` templates playground](https://play.victoriametrics.com/promql/expand-with-exprs)
* [Grafana playground](http://play-grafana.victoriametrics.com:3000/d/4ome8yJmz/node-exporter-on-victoriametrics-demo)
* [PromQL extensions](ExtendedPromQL)
* [MetricsQL](ExtendedPromQL)
* [Single-node version](Single-server-VictoriaMetrics)
* [FAQ](FAQ)
* [Cluster version](Cluster-VictoriaMetrics)
* [Articles](Articles)
* [CaseStudies](Case studies)
* [vmbackup](vmbackup)
* [vmrestore](vmrestore)

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## Prominent features
* Supports [Prometheus querying API](https://prometheus.io/docs/prometheus/latest/querying/api/), so it can be used as Prometheus drop-in replacement in Grafana.
Additionally, VictoriaMetrics extends PromQL with opt-in [useful features](https://github.com/VictoriaMetrics/VictoriaMetrics/wiki/ExtendedPromQL).
VictoriaMetrics implements [MetricsQL](https://github.com/VictoriaMetrics/VictoriaMetrics/wiki/ExtendedPromQL) query language, which is inspired by PromQL.
* Supports global query view. Multiple Prometheus instances may write data into VictoriaMetrics. Later this data may be used in a single query.
* High performance and good scalability for both [inserts](https://medium.com/@valyala/high-cardinality-tsdb-benchmarks-victoriametrics-vs-timescaledb-vs-influxdb-13e6ee64dd6b)
and [selects](https://medium.com/@valyala/when-size-matters-benchmarking-victoriametrics-vs-timescale-and-influxdb-6035811952d4).
@ -395,6 +395,18 @@ VictoriaMetrics supports the following handlers from [Prometheus querying API](h
These handlers can be queried from Prometheus-compatible clients such as Grafana or curl.
VictoriaMetrics accepts additional args for `/api/v1/labels` and `/api/v1/label/.../values` handlers.
See [this feature request](https://github.com/prometheus/prometheus/issues/6178) for details:
* Any number [time series selectors](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors) via `match[]` query arg.
* Optional `start` and `end` query args for limiting the time range for the selected labels or label values.
Additionally VictoriaMetrics provides the following handlers:
* `/api/v1/series/count` - it returns the total number of time series in the database. Note that this handler scans all the inverted index,
so it can be slow if the database contains tens of millions of time series.
* `/api/v1/labels/count` - it returns a list of `label: values_count` entries. It can be used for determining labels with the maximum number of values.
### How to build from sources

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## vmbackup
`vmbackup` creates VictoriaMetrics data backups from [instant snapshots](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/README.md#how-to-work-with-snapshots).
Supported storage systems for backups:
* [GCS](https://cloud.google.com/storage/). Example: `gcs://<bucket>/<path/to/backup>`
* [S3](https://aws.amazon.com/s3/). Example: `s3://<bucket>/<path/to/backup>`
* Any S3-compatible storage such as [MinIO](https://github.com/minio/minio), [Ceph](https://docs.ceph.com/docs/mimic/radosgw/s3/) or [Swift](https://www.swiftstack.com/docs/admin/middleware/s3_middleware.html). See `-customS3Endpoint` command-line flag.
* Local filesystem. Example: `fs://</absolute/path/to/backup>`
Incremental backups and full backups are supported. Incremental backups are created automatically if the destination path already contains data from the previous backup.
Full backups can be sped up with `-origin` pointing to already existing backup on the same remote storage. In this case `vmbackup` makes server-side copy for the shared
data between the existing backup and new backup. This saves time and costs on data transfer.
Backup process can be interrupted at any time. It is automatically resumed from the interruption point when restarting `vmbackup` with the same args.
Backed up data can be restored with [vmrestore](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/app/vmrestore/README.md).
See [this article](https://medium.com/@valyala/speeding-up-backups-for-big-time-series-databases-533c1a927883) for more details.
### Use cases
#### Regular backups
Regular backup can be performed with the following command:
```
vmbackup -storageDataPath=</path/to/victoria-metrics-data> -snapshotName=<local-snapshot> -dst=gcs://<bucket>/<path/to/new/backup>
```
* `</path/to/victoria-metrics-data>` - path to VictoriaMetrics data pointed by `-storageDataPath` command-line flag in single-node VictoriaMetrics or in cluster `vmstorage`.
There is no need to stop VictoriaMetrics for creating backups, since they are performed from immutable [instant snapshots](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/README.md#how-to-work-with-snapshots).
* `<local-snapshot>` is the snapshot to backup. See [how to create instant snapshots](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/README.md#how-to-work-with-snapshots).
* `<bucket>` is already existing name for [GCS bucket](https://cloud.google.com/storage/docs/creating-buckets).
* `<path/to/new/backup>` is the destination path where new backup will be placed.
#### Regular backups with server-side copy from existing backup
If the destination GCS bucket already contains the previous backup at `-origin` path, then new backup can be sped up
with the following command:
```
vmbackup -storageDataPath=</path/to/victoria-metrics-data> -snapshotName=<local-snapshot> -dst=gcs://<bucket>/<path/to/new/backup> -origin=gcs://<bucket>/<path/to/existing/backup>
```
This saves time and network bandwidth costs by performing server-side copy for the shared data from the `-origin` to `-dst`.
#### Incremental backups
Incremental backups are performed if `-dst` points to already existing backup. In this case only new data is uploaded to remote storage.
This saves time and network bandwidth costs when working with big backups:
```
vmbackup -storageDataPath=</path/to/victoria-metrics-data> -snapshotName=<local-snapshot> -dst=gcs://<bucket>/<path/to/existing/backup>
```
#### Smart backups
Smart backups mean storing full daily backups into `YYYYMMDD` folders and creating incremental hourly backup into `latest` folder:
* Run the following command every hour:
```
vmbackup -snapshotName=<latest-snapshot> -dst=gcs://<bucket>/latest
```
Where `<latest-snapshot>` is the latest [snapshot](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/README.md#how-to-work-with-snapshots).
The command will upload only changed data to `gcs://<bucket>/latest`.
* Run the following command once a day:
```
vmbackup -snapshotName=<daily-snapshot> -dst=gcs://<bucket>/<YYYYMMDD> -origin=gcs://<bucket>/latest
```
Where `<daily-snapshot>` is the snapshot for the last day `<YYYYMMDD>`.
This apporach saves network bandwidth costs on hourly backups (since they are incremental) and allows recovering data from either the last hour (`latest` backup)
or from any day (`YYYYMMDD` backups). Note that hourly backup shouldn't run when creating daily backup.
Do not forget removing old snapshots and backups when they are no longer needed for saving storage costs.
### How does it work?
The backup algorithm is the following:
1. Collect information about files in the `-snapshotName`, in the `-dst` and in the `-origin`.
2. Determine files in `-dst`, which are missing in `-snapshotName`, and delete them. These are usually small files, which are already merged into bigger files in the snapshot.
3. Determine files from `-snapshotName`, which are missing in `-dst`. These are usually small new files and bigger merged files.
4. Determine files from step 3, which exist in the `-origin`, and perform server-side copy of these files from `-origin` to `-dst`.
This are usually the biggest and the oldest files, which are shared between backups.
5. Upload the remaining files from setp 3 from `-snapshotName` to `-dst`.
The algorithm splits source files into 100MB chunks in the backup. Each chunk is stored as a separate file in the backup.
Such splitting minimizes the amounts of data to re-transfer after temporary errors.
`vmbackup` relies on [instant snapshot](https://medium.com/@valyala/how-victoriametrics-makes-instant-snapshots-for-multi-terabyte-time-series-data-e1f3fb0e0282) properties:
- All the files in the snapshot are immutable.
- Old files are periodically merged into new files.
- Smaller files have higher probability to be merged.
- Consecutive snapshots share many identical files.
These properties allow performing fast and cheap incremental backups and server-side copying from `-origin` paths.
See [this article](https://medium.com/@valyala/speeding-up-backups-for-big-time-series-databases-533c1a927883) for more details.
`vmbackup` can work improperly or slowly when these properties are violated.
### Troubleshooting
* If the backup is slow, then try setting higher value for `-concurrency` flag. This will increase the number of concurrent workers that upload data to backup storage.
* If `vmbackup` eats all the network bandwidth, then set `-maxBytesPerSecond` to the desired value.
* If `vmbackup` has been interrupted due to temporary error, then just restart it with the same args. It will resume the backup process.
### Advanced usage
Run `vmbackup -help` in order to see all the available options:
```
-concurrency int
The number of concurrent workers. Higher concurrency may reduce backup duration (default 10)
-configFilePath string
Path to file with S3 configs. Configs are loaded from default location if not set.
See https://docs.aws.amazon.com/general/latest/gr/aws-security-credentials.html
-configProfile string
Profile name for S3 configs (default "default")
-credsFilePath string
Path to file with GCS or S3 credentials. Credentials are loaded from default locations if not set.
See https://cloud.google.com/iam/docs/creating-managing-service-account-keys and https://docs.aws.amazon.com/general/latest/gr/aws-security-credentials.html
-customS3Endpoint string
Custom S3 endpoint for use with S3-compatible storages (e.g. MinIO). S3 is used if not set
-dst string
Where to put the backup on the remote storage. Example: gcs://bucket/path/to/backup/dir, s3://bucket/path/to/backup/dir or fs:///path/to/local/backup/dir
-dst can point to the previous backup. In this case incremental backup is performed, i.e. only changed data is uploaded
-loggerLevel string
Minimum level of errors to log. Possible values: INFO, ERROR, FATAL, PANIC (default "INFO")
-maxBytesPerSecond int
The maximum upload speed. There is no limit if it is set to 0
-memory.allowedPercent float
Allowed percent of system memory VictoriaMetrics caches may occupy (default 60)
-origin string
Optional origin directory on the remote storage with old backup for server-side copying when performing full backup. This speeds up full backups
-snapshotName string
Name for the snapshot to backup. See https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/README.md#how-to-work-with-snapshots
-storageDataPath string
Path to VictoriaMetrics data. Must match -storageDataPath from VictoriaMetrics or vmstorage (default "victoria-metrics-data")
-version
Show VictoriaMetrics version
```
### How to build from sources
It is recommended using [binary releases](https://github.com/VictoriaMetrics/VictoriaMetrics/releases) - see `vmutils-*` archives there.
#### Development build
1. [Install Go](https://golang.org/doc/install). The minimum supported version is Go 1.12.
2. Run `make vmbackup` from the root folder of the repository.
It builds `vmbackup` binary and puts it into the `bin` folder.
#### Production build
1. [Install docker](https://docs.docker.com/install/).
2. Run `make vmbackup-prod` from the root folder of the repository.
It builds `vmbackup-prod` binary and puts it into the `bin` folder.
#### Building docker images
Run `make package-vmbackup`. It builds `victoriametrics/vmbackup:<PKG_TAG>` docker image locally.
`<PKG_TAG>` is auto-generated image tag, which depends on source code in the repository.
The `<PKG_TAG>` may be manually set via `PKG_TAG=foobar make package-vmbackup`.

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## vmrestore
`vmrestore` restores data from backups created by [vmbackup](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/app/vmbackup/README.md).
VictoriaMetrics `v1.29.0` and newer versions must be used for working with the restored data.
Restore process can be interrupted at any time. It is automatically resumed from the inerruption point
when restarting `vmrestore` with the same args.
### Usage
VictoriaMetrics must be stopped during the restore process.
```
vmrestore -src=gcs://<bucket>/<path/to/backup> -storageDataPath=<local/path/to/restore>
```
* `<bucket>` is [GCS bucket](https://cloud.google.com/storage/docs/creating-buckets) name.
* `<path/to/backup>` is the path to backup made with [vmbackup](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/app/vmbackup/README.md) on GCS bucket.
* `<local/path/to/restore>` is the path to folder where data will be restored. This folder must be passed
to VictoriaMetrics in `-storageDataPath` command-line flag after the restore process is complete.
The original `-storageDataPath` directory may contain old files. They will be susbstituted by the files from backup.
### Troubleshooting
* If `vmrestore` eats all the network bandwidth, then set `-maxBytesPerSecond` to the desired value.
* If `vmrestore` has been interrupted due to temporary error, then just restart it with the same args. It will resume the restore process.
### Advanced usage
Run `vmrestore -help` in order to see all the available options:
```
-concurrency int
The number of concurrent workers. Higher concurrency may reduce restore duration (default 10)
-configFilePath string
Path to file with S3 configs. Configs are loaded from default location if not set.
See https://docs.aws.amazon.com/general/latest/gr/aws-security-credentials.html
-configProfile string
Profile name for S3 configs (default "default")
-credsFilePath string
Path to file with GCS or S3 credentials. Credentials are loaded from default locations if not set.
See https://cloud.google.com/iam/docs/creating-managing-service-account-keys and https://docs.aws.amazon.com/general/latest/gr/aws-security-credentials.html
-customS3Endpoint string
Custom S3 endpoint for use with S3-compatible storages (e.g. MinIO). S3 is used if not set
-loggerLevel string
Minimum level of errors to log. Possible values: INFO, ERROR, FATAL, PANIC (default "INFO")
-maxBytesPerSecond int
The maximum download speed. There is no limit if it is set to 0
-memory.allowedPercent float
Allowed percent of system memory VictoriaMetrics caches may occupy (default 60)
-src string
Source path with backup on the remote storage. Example: gcs://bucket/path/to/backup/dir, s3://bucket/path/to/backup/dir or fs:///path/to/local/backup/dir
-storageDataPath string
Destination path where backup must be restored. VictoriaMetrics must be stopped when restoring from backup. -storageDataPath dir can be non-empty. In this case only missing data is downloaded from backup (default "victoria-metrics-data")
-version
Show VictoriaMetrics version
```
### How to build from sources
It is recommended using [binary releases](https://github.com/VictoriaMetrics/VictoriaMetrics/releases) - see `vmutils-*` archives there.
#### Development build
1. [Install Go](https://golang.org/doc/install). The minimum supported version is Go 1.12.
2. Run `make vmrestore` from the root folder of the repository.
It builds `vmrestore` binary and puts it into the `bin` folder.
#### Production build
1. [Install docker](https://docs.docker.com/install/).
2. Run `make vmrestore-prod` from the root folder of the repository.
It builds `vmrestore-prod` binary and puts it into the `bin` folder.
#### Building docker images
Run `make package-vmrestore`. It builds `victoriametrics/vmrestore:<PKG_TAG>` docker image locally.
`<PKG_TAG>` is auto-generated image tag, which depends on source code in the repository.
The `<PKG_TAG>` may be manually set via `PKG_TAG=foobar make package-vmrestore`.