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1.12.3
Welcome
Getting Started
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VerneMQ / MQTT Introduction
Installing VerneMQ
Installing on Debian and Ubuntu
Installing on CentOS and RHEL
Running VerneMQ using Docker
Configuring VerneMQ
Introduction
The VerneMQ conf file
Auth using files
Auth using a database
MQTT Options
MQTT Listeners
HTTP Listeners
Non-standard MQTT options
Websockets
Logging
Consumer session balancing
Plugins
Shared subscriptions
Advanced Options
Storage
MQTT Bridge
VerneMQ Clustering
Introduction
Inter-node Communication
Dealing with Netsplits
Live Administration
Introduction
Inspecting and managing sessions
Retained messages
Live reconfiguration
Managing Listeners
HTTP API
Tracing
Monitoring
Introduction
$SYSTree
Graphite
Prometheus
Health Checker
Status Page
Plugin Development
Introduction
Session lifecycle
Subscribe Flow
Publish Flow
Enhanced Auth Flow
Erlang Boilerplate
Lua Scripting Support
Webhooks
Misc
Loadtesting VerneMQ
Not a tuning guide
Change Open File Limits
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Storage
VerneMQ uses Google's LevelDB as a fast storage backend for messages and subscriber information. Each VerneMQ node runs its own embedded LevelDB store.

Configuration of LevelDB memory

There's not much you need to know about LevelDB and VerneMQ. One really important thing to note is that LevelDB manages its own memory. This means that VerneMQ will not allocate and free memory for LevelDB. Instead you'll have to configure a configuration value in vernemq.conf that tells LevelDB how much memory it can use up.
Configuring LevelDB memory:
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leveldb.maximum_memory.percent = 20
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LevelDB means business with its allocated memory. It will eventually end up with the configured max, making it look like there's a memory leak, or even triggering OOM kills. Keep that in mind when configuring the percentage of RAM you give to LevelDB.
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Configuration of LevelDB memory