<p>I am powering a web search using Sphinx, and am getting the following error message while building the indexes:</p>

<blockquote>
  <p>WARNING: sort_hits: merge_block_size=76 kb too low, increasing mem_limit may improve performance</p>
</blockquote>

<p>The problem is I can't find any documentation on where this setting is configured. I'm somewhat versed on Sphinx setup, so I just need to know where the setting is configured.</p>

This is probably happening because you're trying to index too many items at once.  Make sure you're using
ranged queries
.  If you're already using ranged queries, increasing the
```
mem_limit
```
, as it suggests, may help.  The
```
merge_block_size
```
is based on
```
mem_limit
```
and the number of documents.
If you're curious as to how it generates that number, check out the source.  It's freely available.