Merge pull request #4662 from vespa-engine/bratseth/document-threadpool-size

Document the default for search threads on cloud

Author: kkraune

en/reference/applications/services/content.html

@@ -752,7 +752,7 @@ <h2 id="requestthreads">requestthreads</h2>
   <tr>
     <th>search</th>
     <td>Optional</td>
-    <td><strong>Vespa Cloud:</strong> number of allocated vCPUs.
+    <td><strong>Vespa Cloud:</strong> min(vcpu*4 + persearch - 1, vcpu*persearch)<br/>
       <strong>Self-hosted:</strong> 64.</td>
     <td><p id="requestthreads-search">Total size of the match engine thread pool.
       Together with <code>persearch</code>, this determines the maximum number of queries
@@ -766,10 +766,10 @@ <h2 id="requestthreads">requestthreads</h2>
     <td>1</td>
     <td><p id="requestthreads-persearch">
       Maximum number of threads used per search.
-      A higher value reduces query latency for queries where the
-      <a href="../../../performance/sizing-search.html#dynamic-query-work">dynamic query work</a> is high,
-      but also reduces the maximum number of concurrent queries
-      (<code>search / persearch</code>).
+      A higher value reduces the time queries spend in query evaluation, except
+      time spent in ANN which is single-threaded.
+      This number of threads is held for each query for the duration of the query,
+      also when much of the time is spent on single-threaded operations.
       See the <a href="../../../performance/sizing-search.html">Vespa serving scaling guide</a>
       for an introduction of using multiple threads per search per node to reduce query latency.
       Number of threads per search can be adjusted down per <em>rank-profile</em>
@@ -778,8 +778,8 @@ <h2 id="requestthreads">requestthreads</h2>
   <tr>
     <th>summary</th>
     <td>Optional</td>
-    <td><strong>Vespa Cloud:</strong> number of allocated vCPUs.
-      <strong>Self-hosted:</strong> 16.</td>
+    <td><strong>Vespa Cloud:</strong> vcpu
+      <strong>Self-hosted:</strong> 16</td>
     <td><p id="requestthreads-summary">Number of summary threads.</p></td>
   </tr>
   </tbody>