# How to delete or replace metrics in VictoriaMetrics
Data deletion is an operation people expect a database to have. [VictoriaMetrics](https://victoriametrics.com) supports
[delete operation](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#how-to-delete-time-series) but to a limited extent. Due to implementation details, VictoriaMetrics remains an [append-only database](https://en.wikipedia.org/wiki/Append-only), which perfectly fits the case for storing time series data. But the drawback of such architecture is that it is extremely expensive to mutate the data. Hence, `delete` or `update` operations support is very limited. In this guide, we'll walk through the possible workarounds for deleting or changing already written data in VictoriaMetrics.
- [Cluster version of VictoriaMetrics](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html);
- [curl](https://curl.se/docs/manual.html)
- [jq tool](https://stedolan.github.io/jq/)
## How to delete metrics
_Warning: time series deletion is not recommended to use on a regular basis. Each call to delete API could have a performance penalty. The API was provided for one-off operations to deleting malformed data or to satisfy GDPR compliance._
[Delete API](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#how-to-delete-time-series) expects from user to specify [time series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors). So the first thing to do before the deletion is to verify whether the selector matches the correct series.
To check that metrics are present in **VictoriaMetrics Cluster** run the following command:
_Warning: response can return many metrics, so be careful with series selector._
When you're sure [time series selector](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors) is correct, send a POST request to [delete API](https://docs.victoriametrics.com/url-examples.html#apiv1admintsdbdelete_series) with [`match[]=<time-series-selector>`](https://prometheus.io/docs/prometheus/latest/querying/basics/#time-series-selectors) argument. For example:
If operation was successful, the deleted series will stop being [queryable](https://docs.victoriametrics.com/keyConcepts.html#query-data). Storage space for the deleted time series isn't freed instantly - it is freed during subsequent [background merges of data files](https://medium.com/@valyala/how-victoriametrics-makes-instant-snapshots-for-multi-terabyte-time-series-data-e1f3fb0e0282). The background merges may never occur for data from previous months, so storage space won't be freed for historical data. In this case [forced merge](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#forced-merge) may help freeing up storage space.
To trigger [forced merge](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#forced-merge) on VictoriaMetrics Cluster run the following command:
<divclass="with-copy"markdown="1">
```console
curl -v -X POST http://vmstorage:8482/internal/force_merge
- [delete time series from a database](https://docs.victoriametrics.com/url-examples.html#apiv1admintsdbdelete_series);
- [import saved file to VictoriaMetrics](https://docs.victoriametrics.com/url-examples.html#apiv1import).
### Export metrics
For example, let's export metric for `node_memory_MemTotal_bytes` with labels `instance="node-exporter:9100"` and `job="hostname.com"`:
<divclass="with-copy"markdown="1">
```console
curl -X POST -g http://vmselect:8481/select/0/prometheus/api/v1/export -d 'match[]=node_memory_MemTotal_bytes{instance="node-exporter:9100", job="hostname.com"}' > data.jsonl
```
</div>
To check that exported file contains time series we can use [cat](https://man7.org/linux/man-pages/man1/cat.1.html) and [jq](https://stedolan.github.io/jq/download/)
<divclass="with-copy"markdown="1">
```console
cat data.jsonl | jq
```
</div>
The expected output will look like:
```json
{
"metric": {
"__name__": "node_memory_MemTotal_bytes",
"job": "hostname.com",
"instance": "node-exporter:9100"
},
"values": [
33604390912,
33604390912,
33604390912,
33604390912
],
"timestamps": [
1656669031378,
1656669032378,
1656669033378,
1656669034378
]
}
```
In this example, we will replace the values of `node_memory_MemTotal_bytes` from `33604390912` to `17179869184` (from 32Gb to 16Gb) via [sed](https://linux.die.net/man/1/sed), but it can be done in any of the available ways.
```console
sed -i 's/33604390912/17179869184/g' data.jsonl
```
Let's check the changes in data.jsonl with `cat`:
```console
cat data.jsonl | jq
```
The expected output will be the next:
```json
{
"metric": {
"__name__": "node_memory_MemTotal_bytes",
"job": "hostname.com",
"instance": "node-exporter:9100"
},
"values": [
17179869184,
17179869184,
17179869184,
17179869184
],
"timestamps": [
1656669031378,
1656669032378,
1656669033378,
1656669034378
]
}
```
### Delete metrics
See [How-to-delete-metrics](https://docs.victoriametrics.com/guides/guide-delete-or-replace-metrics.html#how-to-delete-metrics) from the previous paragraph
### Import metrics
Victoriametrics supports a lot of [ingestion protocols](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#how-to-import-time-series-data) and we will use [import from JSON line format](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html#how-to-import-data-in-json-line-format).
The next command will import metrics from `data.jsonl` to VictoriaMetrics:
<divclass="with-copy"markdown="1">
```console
curl -v -X POST http://vminsert:8480/insert/0/prometheus/api/v1/import -T data.jsonl
```
</div>
### Check imported metrics
<divclass="with-copy"markdown="1">
```console
curl -X POST -g http://vmselect:8481/select/0/prometheus/api/v1/export -d match[]=node_memory_MemTotal_bytes
