man: document journal rate limit burst multiplier

The actual burst limit is modified by the remaining disk space. This
isn't mentioned anywhere in the available documentation and might be a
source of surprise for an end user expecting certain behaviors.
This commit is contained in:
Charles (Chas) Williams 2019-11-21 10:26:24 -05:00 committed by Zbigniew Jędrzejewski-Szmek
parent 26601a2a17
commit c0dd326953
1 changed files with 45 additions and 0 deletions

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@ -139,6 +139,51 @@
<literal>us</literal>. To turn off any kind of rate limiting,
set either value to 0.</para>
<para>Note that the effective rate limit is multiplied with a
factor derived from the available free disk space for the journal.
Currently, this factor is calculated using the base 2 logarithm.</para>
<table>
<title>Example <varname>RateLimitBurst=</varname> rate
modifications by the available disk space</title>
<tgroup cols='2'>
<colspec colname='freespace' />
<colspec colname='multiplier' />
<thead>
<row>
<entry>Available Disk Space</entry>
<entry>Burst Multiplier</entry>
</row>
</thead>
<tbody>
<row>
<entry>&lt;= 1MB</entry>
<entry>1</entry>
</row>
<row>
<entry>&lt;= 16MB</entry>
<entry>2</entry>
</row>
<row>
<entry>&lt;= 256MB</entry>
<entry>3</entry>
</row>
<row>
<entry>&lt;= 4GB</entry>
<entry>4</entry>
</row>
<row>
<entry>&lt;= 64GB</entry>
<entry>5</entry>
</row>
<row>
<entry>&lt;= 1TB</entry>
<entry>6</entry>
</row>
</tbody>
</tgroup>
</table>
<para>If a service provides rate limits for itself through
<varname>LogRateLimitIntervalSec=</varname> and/or <varname>LogRateLimitBurst=</varname>
in <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,