[delete operation](https://docs.victoriametrics.com/single-server-victoriametrics/#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.
_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/#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.
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/#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/#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/#forced-merge) may help freeing up storage space.
To trigger [forced merge](https://docs.victoriametrics.com/single-server-victoriametrics/#forced-merge) on VictoriaMetrics Cluster run the following command:
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/):
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:
See [How-to-delete-metrics](https://docs.victoriametrics.com/guides/guide-delete-or-replace-metrics.html#how-to-delete-metrics) from the previous paragraph.
VictoriaMetrics supports a lot of [ingestion protocols](https://docs.victoriametrics.com/single-server-victoriametrics/#how-to-import-time-series-data) and we will use [import from JSON line format](https://docs.victoriametrics.com/single-server-victoriametrics/#how-to-import-data-in-json-line-format).
Please note, importing data with old timestamps is called **backfilling** and may require resetting caches as described [here](https://docs.victoriametrics.com/#backfilling).
