* Prometheus-compatible service discovery and target scraping can be done with [vmagent](https://docs.victoriametrics.com/vmagent/) and with single-node VictoriaMetrics. See [these docs](https://docs.victoriametrics.com/#how-to-scrape-prometheus-exporters-such-as-node-exporter).
* vmagent provides independent disk-backed buffers for each configured remote storage (see `-remoteWrite.url`). This means that slow or temporarily unavailable storage
doesn't prevent it from sending data to healthy storage in parallel. Prometheus uses a single shared buffer for all the configured remote storage systems (see `remote_write->url`)
Both [vmagent](https://docs.victoriametrics.com/vmagent/) and [Prometheus agent](https://prometheus.io/blog/2021/11/16/agent/) serve the same purpose – to efficiently scrape Prometheus-compatible targets at the edge. They have the following differences:
* Prometheus agent supports only pull-based data collection (e.g. it can scrape Prometheus-compatible targets), while vmagent supports both pull and push data collection – it can accept data via many popular data ingestion protocols such as InfluxDB line protocol, Graphite protocol, OpenTSDB protocol, DataDog protocol, Prometheus protocol, CSV and JSON – see [these docs](https://docs.victoriametrics.com/vmagent/#features).
* vmagent can easily scale horizontally to multiple instances for scraping a big number of targets – see [these docs](https://docs.victoriametrics.com/vmagent/#scraping-big-number-of-targets).
## How does VictoriaMetrics compare to other remote storage solutions for Prometheus such as [M3DB](https://github.com/m3db/m3), [Thanos](https://github.com/thanos-io/thanos), [Cortex](https://github.com/cortexproject/cortex), [Mimir](https://github.com/grafana/mimir), etc.?
from [PromCon 2019](https://promcon.io/2019-munich/talks/remote-write-storage-wars/)
* [Grafana Mimir and VictoriaMetrics: performance tests](https://victoriametrics.com/blog/mimir-benchmark/)
* [VictoriaMetrics: scaling to 100 million metrics per second](https://www.slideshare.net/NETWAYS/osmc-2022-victoriametrics-scaling-to-100-million-metrics-per-second-by-aliaksandr-valialkin)
* QuestDB needs more than 20x storage space than VictoriaMetrics. This translates to higher storage costs and slower queries over historical data, which must be read from the disk.
* QuestDB is much harder to set up and operate than VictoriaMetrics. Compare [setup instructions for QuestDB](https://questdb.io/docs/get-started/binaries) to [setup instructions for VictoriaMetrics](https://docs.victoriametrics.com/#how-to-start-victoriametrics).
* VictoriaMetrics provides the [MetricsQL](https://docs.victoriametrics.com/metricsql/) query language, which is better suited for typical queries over time series data than the SQL-like query language provided by QuestDB. See [this article](https://valyala.medium.com/promql-tutorial-for-beginners-9ab455142085) for details.
* VictoriaMetrics can be queried via the [Prometheus querying API](https://docs.victoriametrics.com/#prometheus-querying-api-usage) and via [Graphite's API](https://docs.victoriametrics.com/#graphite-api-usage).
* Thanks to PromQL support, VictoriaMetrics [can be used as a drop-in replacement for Prometheus in Grafana](https://docs.victoriametrics.com/#grafana-setup), while QuestDB needs a full rewrite of existing dashboards in Grafana.
* Thanks to Prometheus' remote_write API support, VictoriaMetrics can be used as a long-term storage for Prometheus or for [vmagent](https://docs.victoriametrics.com/vmagent/), while QuestDB has no integration with Prometheus.
* QuestDB [supports a smaller range of popular data ingestion protocols](https://questdb.io/docs/develop/insert-data) compared to VictoriaMetrics (compare to [the list of supported data ingestion protocols for VictoriaMetrics](https://docs.victoriametrics.com/#how-to-import-time-series-data)).
* [VictoriaMetrics supports backfilling (e.g. storing historical data) out of the box](https://docs.victoriametrics.com/#backfilling), while QuestDB provides [very limited support for backfilling](https://questdb.io/blog/2021/05/10/questdb-release-6-0-tsbs-benchmark#the-problem-with-out-of-order-data).
* Both systems support multi-tenancy out of the box. See [the corresponding docs for VictoriaMetrics](https://docs.victoriametrics.com/cluster-victoriametrics/#multitenancy).
* Both systems support data replication. See [replication in Cortex](https://github.com/cortexproject/cortex/blob/fe56f1420099aa1bf1ce09316c186e05bddee879/docs/architecture.md#hashing) and [replication in VictoriaMetrics](https://docs.victoriametrics.com/cluster-victoriametrics/#replication-and-data-safety).
* Both systems scale horizontally to multiple nodes. See [these docs](https://docs.victoriametrics.com/cluster-victoriametrics/#cluster-resizing-and-scalability) for details.
* Both systems can be queried via the [Prometheus querying API](https://prometheus.io/docs/prometheus/latest/querying/api/) and integrate perfectly with Grafana.
* Cortex may lose up to 12 hours of recent data on Ingestor failure – see [the corresponding docs](https://github.com/cortexproject/cortex/blob/fe56f1420099aa1bf1ce09316c186e05bddee879/docs/architecture.md#ingesters-failure-and-data-loss).
* Cortex is usually slower and requires more CPU and RAM than VictoriaMetrics. See [this talk from adidas at PromCon 2019](https://promcon.io/2019-munich/talks/remote-write-storage-wars/) and [other case studies](https://docs.victoriametrics.com/casestudies/).
* VictoriaMetrics accepts data in multiple popular data ingestion protocols additionally to Prometheus remote_write protocol – InfluxDB, OpenTSDB, Graphite, CSV, JSON, native binary.
* VictoriaMetrics provides the [MetricsQL](https://docs.victoriametrics.com/metricsql/) query language, while Cortex provides the [PromQL](https://prometheus.io/docs/prometheus/latest/querying/basics/) query language.
while Thanos uses a non-standard [sidecar](https://github.com/thanos-io/thanos/blob/master/docs/components/sidecar.md) which must run alongside each Prometheus instance.
* The Thanos sidecar requires disabling data compaction in Prometheus, which may hurt Prometheus performance and increase RAM usage. See [these docs](https://thanos.io/tip/components/sidecar.md/) for more details.
* Thanos stores data in object storage (Amazon S3 or Google GCS), while VictoriaMetrics stores data in block storage
* Thanos may lose up to 2 hours of recent data, which wasn't uploaded yet to object storage. VictoriaMetrics may lose only a few seconds of recent data,
which hasn't been synced to persistent storage yet. See [this article for details](https://medium.com/@valyala/wal-usage-looks-broken-in-modern-time-series-databases-b62a627ab704).
* Thanos may be harder to set up and operate compared to VictoriaMetrics, since it has more moving parts, which can be connected with fewer reliable networks.
* Thanos is usually slower and requires more CPU and RAM than VictoriaMetrics. See [this talk from adidas at PromCon 2019](https://promcon.io/2019-munich/talks/remote-write-storage-wars/).
* VictoriaMetrics accepts data via multiple popular data ingestion protocols in addition to the Prometheus remote_write protocol – InfluxDB, OpenTSDB, Graphite, CSV, JSON, native binary.
* VictoriaMetrics provides the [MetricsQL](https://docs.victoriametrics.com/metricsql/) query language, while Thanos provides the [PromQL](https://prometheus.io/docs/prometheus/latest/querying/basics/) query language.
* VictoriaMetrics requires [10x less RAM](https://medium.com/@valyala/insert-benchmarks-with-inch-influxdb-vs-victoriametrics-e31a41ae2893) and it [works faster](https://medium.com/@valyala/measuring-vertical-scalability-for-time-series-databases-in-google-cloud-92550d78d8ae).
* VictoriaMetrics needs lower amounts of storage space than InfluxDB for production data.
* VictoriaMetrics doesn't support InfluxQL or Flux but provides a better query language – [MetricsQL](https://docs.victoriametrics.com/metricsql/). See [this tutorial](https://medium.com/@valyala/promql-tutorial-for-beginners-9ab455142085) for details.
* VictoriaMetrics accepts data in multiple popular data ingestion protocols in addition to InfluxDB – Prometheus remote_write, OpenTSDB, Graphite, CSV, JSON, native binary.
* TimescaleDB insists on using SQL as a query language. While SQL is more powerful than PromQL, this power is rarely required during typical usages of a TSDB. Real-world queries usually [look clearer and simpler when written in PromQL than in SQL](https://medium.com/@valyala/promql-tutorial-for-beginners-9ab455142085).
* VictoriaMetrics requires [up to 70x less storage space compared to TimescaleDB](https://medium.com/@valyala/when-size-matters-benchmarking-victoriametrics-vs-timescale-and-influxdb-6035811952d4) for storing the same amount of time series data. The gap in storage space usage can be lowered from 70x to 3x if [compression in TimescaleDB is properly configured](https://docs.timescale.com/latest/using-timescaledb/compression) (it isn't an easy task in general :)).
* VictoriaMetrics requires up to 10x less CPU and RAM resources than TimescaleDB for processing production data. See [this article](https://abiosgaming.com/press/high-cardinality-aggregations/) for details.
* TimescaleDB is [harder to set up, configure and operate](https://docs.timescale.com/timescaledb/latest/how-to-guides/install-timescaledb/self-hosted/ubuntu/installation-apt-ubuntu/) than VictoriaMetrics (see [how to run VictoriaMetrics](https://docs.victoriametrics.com/#how-to-start-victoriametrics)).
* VictoriaMetrics accepts data in multiple popular data ingestion protocols – InfluxDB, OpenTSDB, Graphite, CSV – while TimescaleDB supports only SQL inserts.
* VictoriaMetrics can be queried via [Graphite's API](https://docs.victoriametrics.com/#graphite-api-usage).
## Does VictoriaMetrics use Prometheus technologies like other clustered TSDBs built on top of Prometheus such as [Thanos](https://github.com/thanos-io/thanos) or [Cortex](https://github.com/cortexproject/cortex)?
The architecture is [optimized for storing and querying large amounts of time series data with high cardinality](https://medium.com/devopslinks/victoriametrics-creating-the-best-remote-storage-for-prometheus-5d92d66787ac). VictoriaMetrics storage uses [certain ideas from ClickHouse](https://medium.com/@valyala/how-victoriametrics-makes-instant-snapshots-for-multi-terabyte-time-series-data-e1f3fb0e0282). Special thanks to [Alexey Milovidov](https://github.com/alexey-milovidov).
## Why doesn't VictoriaMetrics support the [Prometheus remote read API](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#%3Cremote_read%3E)?
Prometheus' remote read API isn't intended for querying foreign data – aka `global query view`. See [this issue](https://github.com/prometheus/prometheus/issues/4456) for details.
So just query VictoriaMetrics directly via [vmui](https://docs.victoriametrics.com/#vmui), the [Prometheus Querying API](https://docs.victoriametrics.com/#prometheus-querying-api-usage)
VictoriaMetrics is able to handle data from hundreds of millions of IoT sensors and industrial sensors.
It supports [high cardinality data](https://medium.com/@valyala/high-cardinality-tsdb-benchmarks-victoriametrics-vs-timescaledb-vs-influxdb-13e6ee64dd6b),
perfectly [scales up on a single node](https://medium.com/@valyala/measuring-vertical-scalability-for-time-series-databases-in-google-cloud-92550d78d8ae)
Single-node VictoriaMetrics scales vertically though, e.g. its capacity and performance scales almost linearly when increasing
available CPU, RAM, disk IO and disk space. See [an article about vertical scalability of a single-node VictoriaMetrics](https://valyala.medium.com/measuring-vertical-scalability-for-time-series-databases-in-google-cloud-92550d78d8ae).
* Single-node VictoriaMetrics provides higher capacity and performance comparing to cluster version of VictoriaMetrics
when running on the same hardware with the same amounts of CPU and RAM, since it has no overhead on data transfer
between cluster components over the network.
See also [which type of VictoriaMetrics is recommended to use](#which-victoriametrics-type-is-recommended-for-use-in-production---single-node-or-cluster).
See [these docs](https://docs.victoriametrics.com/cluster-victoriametrics/#multitenancy). Multitenancy is supported only by the [cluster version](https://docs.victoriametrics.com/cluster-victoriametrics/) of VictoriaMetrics.
All the VictoriaMetrics components provide command-line flags to control the size of internal buffers and caches: `-memory.allowedPercent` and `-memory.allowedBytes` (pass `-help` to any VictoriaMetrics component in order to see the description for these flags). These limits don't take into account additional memory, which may be needed for processing incoming queries. Hard limits may be enforced only by the OS via [cgroups](https://en.wikipedia.org/wiki/Cgroups), Docker (see [these docs](https://docs.docker.com/config/containers/resource_constraints)) or Kubernetes (see [these docs](https://kubernetes.io/docs/concepts/configuration/manage-resources-containers)).
VictoriaMetrics is included in [OpenBSD](https://github.com/openbsd/ports/blob/c1bfea520bbb30d6e5f8d0f09115ace341f820d6/infrastructure/db/user.list#L383)
and [FreeBSD](https://www.freebsd.org/cgi/ports.cgi?query=victoria&stype=all) ports so just install it from there
or use pre-built binaries from [releases page](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/latest).
A time series is uniquely identified by its name plus a set of its labels. For example, `temperature{city="NY",country="US"}` and `temperature{city="SF",country="US"}`
are two distinct series, since they differ by the `city` label. A time series is considered active if it receives at least a single new sample during the last hour.
The number of active time series is displayed on the official Grafana dashboard for VictoriaMetrics - see [these docs](https://docs.victoriametrics.com/#monitoring) for details.
If old time series are constantly substituted by new time series at a high rate, then such a state is called `high churn rate`. High churn rate has the following negative consequences:
* Increased size of inverted index, which is stored at `<-storageDataPath>/indexdb`, since the inverted index contains entries for every label of every time series with at least a single ingested sample.
The solution against high churn rate is to identify and eliminate labels with frequently changed values.
[Cardinality explorer](https://docs.victoriametrics.com/#cardinality-explorer) can help determining these labels.
The official Grafana dashboards for VictoriaMetrics contain graphs for churn rate - see [these docs](https://docs.victoriametrics.com/#monitoring) for details.
High cardinality usually means a high number of [active time series](#what-is-an-active-time-series). High cardinality may lead to high memory usage
and/or to a high percentage of [slow inserts](#what-is-a-slow-insert). The source of high cardinality is usually a label with
a large number of unique values, which presents a big share of the ingested time series. Examples of such labels:
*`user_id`
*`url`
*`ip`
The solution is to identify and remove the source of high cardinality with the help of [cardinality explorer](https://docs.victoriametrics.com/#cardinality-explorer).
The official Grafana dashboards for VictoriaMetrics contain graphs, which show the number of active time series -
see [these docs](https://docs.victoriametrics.com/#monitoring) for details.
VictoriaMetrics maintains in-memory cache for mapping of [active time series](#what-is-an-active-time-series) into internal series ids.
The cache size depends on the available memory for VictoriaMetrics in the host system. If the information about all the active time series doesn't fit the cache,
then VictoriaMetrics needs to read and unpack the information from disk on every incoming sample for time series missing in the cache.
This operation is much slower than the cache lookup, so such an insert is named a `slow insert`.
A high percentage of slow inserts on the [official dashboard for VictoriaMetrics](https://docs.victoriametrics.com/#monitoring) indicates
a memory shortage for the current number of [active time series](#what-is-an-active-time-series). Such a condition usually leads
to a significant slowdown for data ingestion and to significantly increased disk IO and CPU usage.
The solution is to add more memory or to reduce the number of [active time series](#what-is-an-active-time-series).
[Cardinality explorer](https://docs.victoriametrics.com/#cardinality-explorer) can be helpful for locating the source of high number of active time series.
VictoriaMetrics also provides [query tracer](https://docs.victoriametrics.com/#query-tracing) and [cardinality explorer](https://docs.victoriametrics.com/#cardinality-explorer),
- If the current workload cannot be handled by a single-node VictoriaMetrics. For example, if you are going to ingest hundreds of millions of active time series
since its capacity can [scale horizontally with the number of nodes in the cluster](https://docs.victoriametrics.com/cluster-victoriametrics/#cluster-resizing-and-scalability).
## How to migrate data from single-node VictoriaMetrics to cluster version?
Single-node VictoriaMetrics stores data on disk in slightly different format comparing to cluster version of VictoriaMetrics.
So it is impossible to just copy the on-disk data from `-storageDataPath` directory from single-node VictoriaMetrics to a `vmstorage` node in VictoriaMetrics cluster.
If you need migrating data from single-node VictoriaMetrics to cluster version, then [follow these instructions](https://docs.victoriametrics.com/vmctl/#migrating-data-from-victoriametrics).
[MetricsQL](https://docs.victoriametrics.com/metricsql/) provides better user experience than PromQL. It fixes a few annoying issues in PromQL. This prevents MetricsQL to be 100% compatible with PromQL. See [this article](https://medium.com/@romanhavronenko/victoriametrics-promql-compliance-d4318203f51e) for details.
Please use the [whisper-to-graphite](https://github.com/bzed/whisper-to-graphite) tool for reading data from Graphite and pushing them to VictoriaMetrics via [Graphite's import API](https://docs.victoriametrics.com/#how-to-send-data-from-graphite-compatible-agents-such-as-statsd).
There could be a slight difference in stored values for time series. Due to different compression algorithms, VM may reduce the precision for float values with more than 12 significant decimal digits. Please see [this article](https://valyala.medium.com/evaluating-performance-and-correctness-victoriametrics-response-e27315627e87).
The query engine may behave differently for some functions. Please see [this article](https://medium.com/@romanhavronenko/victoriametrics-promql-compliance-d4318203f51e).
[Deduplication](https://docs.victoriametrics.com/#deduplication) is a special case of zero-offset [downsampling](https://docs.victoriametrics.com/#downsampling). So, if both downsampling and deduplication are enabled, then deduplication is replaced by zero-offset downsampling
## How to upgrade or downgrade VictoriaMetrics without downtime?
Single-node VictoriaMetrics cannot be restarted / upgraded or downgraded without downtime, since it needs to be gracefully shut down and then started again. See [how to upgrade VictoriaMetrics](https://docs.victoriametrics.com/#how-to-upgrade-victoriametrics).
[Cluster version of VictoriaMetrics](https://docs.victoriametrics.com/cluster-victoriametrics/) can be restarted / upgraded / downgraded without downtime according to [these instructions](https://docs.victoriametrics.com/cluster-victoriametrics/#updating--reconfiguring-cluster-nodes).
## Why VictoriaMetrics misses automatic data re-balancing between vmstorage nodes?
VictoriaMetrics doesn't rebalance data between `vmstorage` nodes when new `vmstorage` nodes are added to the cluster.
This means that newly added `vmstorage` nodes will have less data at `-storageDataPath` comparing to the old `vmstorage` nodes
until the historical data is removed from the old `vmstorage` nodes when it goes outside the configured [retention](https://docs.victoriametrics.com/#retention).
The automatic rebalancing is the process of moving data between `vmstorage` nodes, so every node has the same amounts of data eventually.
It is disabled by default because it may consume additional CPU, network bandwidth and disk IO at `vmstorage` nodes for long periods of time,
which, in turn, can negatively impact VictoriaMetrics cluster availability.
Additionally, it is unclear how to handle the automatic re-balancing if cluster configuration changes when the re-balancing is in progress.
The amounts of data stored in `vmstorage` becomes equal among old `vmstorage` nodes and new `vmstorage` nodes
after historical data is removed from the old `vmstorage` nodes because it goes outside of configured [retention](https://docs.victoriametrics.com/#retention).
The data ingestion load becomes even between old `vmstorage` nodes and new `vmstorage` nodes almost immediately
after adding new `vmstorage` nodes to the cluster, since `vminsert` nodes evenly distribute incoming time series
among the nodes specified in `-storageNode` command-line flag. The newly added `vmstorage` nodes may experience
increased load during the first couple of minutes because they need to register [active time series](https://docs.victoriametrics.com/faq/#what-is-an-active-time-series).
