<p></p>
<p>According to the <a href="https://osm2pgsql.org/doc/manual.html#caching" rel="nofollow">docs</a>:</p>
<pre><code>The rule of thumb in slim mode is as follows: use the size of the PBF file you are trying to import or about 75% of RAM, whatever is smaller.
</code></pre>
<p>But in fact seems that cache size must be above twice lager then source file.<br>
I've made tests on 2 pbf-files and it shown that for cache size equal to source file size import speed for ways just 30-40% from max possible.</p>
<p><a target="_blank" rel="noopener noreferrer" href="https://user-images.githubusercontent.com/603401/111852498-3670ee80-8928-11eb-8ff3-4be8090798d7.png"><img src="https://user-images.githubusercontent.com/603401/111852498-3670ee80-8928-11eb-8ff3-4be8090798d7.png" alt="image" style="max-width:100%;"></a></p>
<p><a target="_blank" rel="noopener noreferrer" href="https://user-images.githubusercontent.com/603401/111852512-44267400-8928-11eb-9033-60eea746a200.png"><img src="https://user-images.githubusercontent.com/603401/111852512-44267400-8928-11eb-9033-60eea746a200.png" alt="image" style="max-width:100%;"></a></p>
<p><a href="https://docs.google.com/spreadsheets/d/1IjCndMOyr6cM2FDRu53ASZdIR6ZdmUeqoREf-V9TGGk/edit?usp=sharing" rel="nofollow">Google sheet with tests results</a>.</p>

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