Use this documentation with care! It describes
the outdated version 7, which was actively
developed around 2014 and is considered dead by the
This documentation reflects the latest update of the v7-stable branch. It describes the 7.6.8 version, which was never released. As such, it contains some content that does not apply to any released version.
To obtain the doc that properly matches your installed v7 version, obtain the doc set from your distro. Each version of rsyslog contained the version that exactly matches it.
As general advise, it is strongly suggested to upgrade to the current version supported by the rsyslog project. The current version can always be found on the right-hand side info box on the rsyslog web site.
Note that there is only limited rsyslog community support available for the outdated v7 version (officially we do not support it at all, but we usually are able to answer simple questions). If you need to stick with v7, it probably is best to ask your distribution for support.
Type: global configuration directive
This allows to specify the maximum size of the message queue. This directive is only available when rsyslogd has been compiled with multithreading support. In this mode, receiver and output modules are de-coupled via an in-memory queue. This queue buffers messages when the output modules are not capable to process them as fast as they are received. Once the queue size is exhausted, messages will be dropped. The slower the output (e.g. MySQL), the larger the queue should be. Buffer space for the actual queue entries is allocated on an as-needed basis. Please keep in mind that a very large queue may exhaust available system memory and swap space. Keep this in mind when configuring the max size. The actual size of a message depends largely on its content and the originator. As a rule of thumb, typically messages should not take up more then roughly 1k (this is the memory structure, not what you see in a network dump!). For typical linux messages, 512 bytes should be a good bet. Please also note that there is a minimal amount of memory taken for each queue entry, no matter if it is used or not. This is one pointer value, so on 32bit systems, it should typically be 4 bytes and on 64bit systems it should typically be 8 bytes. For example, the default queue size of 10,000 entries needs roughly 40k fixed overhead on a 32 bit system.
$MainMsgQueueSize 100000 # 100,000 may be a value to handle burst traffic