netdata/docs/netdata-agent/sizing-netdata-agents/ram-requirements.md

RAM Utilization

Using the default Database Tier configuration, Netdata needs about 16KiB per unique metric collected, independently of the data collection frequency.

Children

Netdata by default should need 100MB to 200MB of RAM, depending on the number of metrics being collected.

This number can be lowered by limiting the number of Database Tiers or switching Database modes. For more information, check the Database section of our documentation.

Parents

Description	Scope	RAM Required	Notes
metrics with retention	time-series in the db	1 KiB	Metadata and indexes
metrics currently collected	time-series collected	20 KiB	16 KiB for db + 4 KiB for collection structures
metrics with Machine Learning Models	time-series collected	5 KiB	The trained models per dimension
nodes with retention	nodes in the db	10 KiB	Metadata and indexes
nodes currently received	nodes collected	512 KiB	Structures and reception buffers
nodes currently sent	nodes collected	512 KiB	Structures and dispatch buffers

These numbers vary depending on name length, the number of dimensions per instance and per context, the number and length of the labels added, the number of Machine Learning models maintained and similar parameters. For most use cases, they represent the worst case scenario, so you may find out Netdata actually needs less than that.

Each metric currently being collected needs (1 index + 20 collection + 5 ml) = 26 KiB. When it stops being collected, it needs 1 KiB (index).

Each node currently being collected needs (10 index + 512 reception + 512 dispatch) = 1034 KiB. When it stops being collected, it needs 10 KiB (index).

Example

A Netdata cluster (two Parents) has one million currently collected metrics from 500 nodes, and 10 million archived metrics from 5000 nodes:

Description	Entries	RAM per Entry	Total RAM
metrics with retention	11 million	1 KiB	10742 MiB
metrics currently collected	1 million	20 KiB	19531 MiB
metrics with Machine Learning Models	1 million	5 KiB	4883 MiB
nodes with retention	5500	10 KiB	52 MiB
nodes currently received	500	512 KiB	256 MiB
nodes currently sent	500	512 KiB	256 MiB
Memory required per node			35.7 GiB

In highly volatile environments (like Kubernetes clusters), Database retention can significantly affect memory usage. Usually, reducing retention on higher Database Tiers helps to reduce memory usage.

Database Size

Netdata supports memory ballooning to automatically adjust its Database memory size based on the number of time-series concurrently being collected.

The general formula, with the default configuration of Database Tiers, is:

memory = UNIQUE_METRICS x 16KiB + CONFIGURED_CACHES

The default CONFIGURED_CACHES is 32MiB.

For one million concurrently collected time-series (independently of their data collection frequency), the required memory is 16 GiB. In detail:

UNIQUE_METRICS = 1000000
CONFIGURED_CACHES = 32MiB

(UNIQUE_METRICS * 16KiB / 1024 in MiB) + CONFIGURED_CACHES =
( 1000000       * 16KiB / 1024 in MiB) + 32 MiB            =
15657 MiB =
about 16 GiB

Parents that also act as systemd-journal Logs centralization points

Logs usually require significantly more disk space and I/O bandwidth than metrics. For optimal performance, we recommend to store metrics and logs on separate, independent disks.

Netdata uses direct-I/O for its Database to not pollute the system caches with its own data.

To optimize disk I/O, Netdata maintains its own private caches. The default settings of these caches are automatically adjusted to the minimum required size for acceptable metrics query performance.

systemd-journal on the other hand, relies on operating system caches for improving the query performance of logs. When the system lacks free memory, querying logs leads to increased disk I/O.

If you are experiencing slow responses and increased disk reads when metrics queries run, we suggest dedicating some more RAM to Netdata.

We frequently see that the following strategy gives the best results:

1. Start the Netdata Parent, send all the load you expect it to have and let it stabilize for a few hours. Netdata will now use the minimum memory it believes is required for smooth operation.
2. Check the available system memory.
3. Set the page cache in netdata.conf to use 1/3 of the available memory.

This will allow Netdata queries to have more caches, while leaving plenty of available memory of logs and the operating system.