<p>So, I ran diffs on a full planet. Unfortunately the results with the normal branch <a href="https://github.com/openstreetmap/osm2pgsql/commit/5ba712d15ba611e502840374b1bacbc72d830042" class="commit-link"><tt>5ba712d</tt></a> and threading <a href="https://github.com/openstreetmap/osm2pgsql/commit/a5755430392af3459d06ede91e9498b10bd18ae1" class="commit-link"><tt>a575543</tt></a> are not the same.</p>

<p>They're pretty close. <code>planet_osm_ways</code>, <code>planet_osm_rels</code>, <code>planet_osm_point</code>, and <code>planet_osm_polygon</code> all pass my tests, with all the statistics I compute being the same with both branches. <code>planet_osm_line</code> and <code>planet_osm_roads</code> differ. If forced to guess, I would guess it's something related to splitting long ways.</p>

<p>The relevant queries are</p>

<div class="highlight highlight-sql"><pre><span class="k">SELECT</span> <span class="k">COUNT</span><span class="p">(</span><span class="o">*</span><span class="p">),</span> <span class="k">SUM</span><span class="p">(</span><span class="n">ST_Length</span><span class="p">(</span><span class="n">way</span><span class="p">))</span> <span class="k">AS</span> <span class="n">st_length</span> <span class="k">FROM</span> <span class="n">planet_osm_line</span><span class="p">;</span>
<span class="k">SELECT</span> <span class="k">COUNT</span><span class="p">(</span><span class="o">*</span><span class="p">),</span> <span class="k">SUM</span><span class="p">(</span><span class="n">ST_Length</span><span class="p">(</span><span class="n">way</span><span class="p">))</span> <span class="k">AS</span> <span class="n">st_length</span> <span class="k">FROM</span> <span class="n">planet_osm_roads</span><span class="p">;</span>

<span class="k">SELECT</span> <span class="k">COUNT</span><span class="p">(</span><span class="o">*</span><span class="p">),</span> <span class="k">SUM</span><span class="p">(</span><span class="n">ST_Length</span><span class="p">(</span><span class="n">way</span><span class="p">))</span> <span class="k">AS</span> <span class="n">st_length</span> <span class="k">FROM</span> <span class="n">planet_osm_line</span> <span class="k">WHERE</span> <span class="n">highway</span><span class="o">=</span><span class="s1">'primary'</span><span class="p">;</span>
<span class="k">SELECT</span> <span class="k">COUNT</span><span class="p">(</span><span class="o">*</span><span class="p">),</span> <span class="k">SUM</span><span class="p">(</span><span class="n">ST_Length</span><span class="p">(</span><span class="n">way</span><span class="p">))</span> <span class="k">AS</span> <span class="n">st_length</span> <span class="k">FROM</span> <span class="n">planet_osm_roads</span> <span class="k">WHERE</span> <span class="n">highway</span><span class="o">=</span><span class="s1">'primary'</span><span class="p">;</span>
</pre></div>

<p>The results are</p>

<pre><code>Test                  Normal N=8 604      Threaded N=8 604   Difference
line count            82988137            82998741           -10604
line length           115470181512.839    115585071070.389   -114889557.6
road count            7743627             7744565            -938
road length           41246103355.6413    41261720915.1192   -15617559.48
primary line count    1320509             1320575            -66
primary line legnth   2734979047.75017    2734985654.309     -6606.55883
primary road count    1320509             1320575            -66
primary road length   2734979047.75017    2734985654.309     -6606.55883
</code></pre>

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