Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/1377#discussion_r15211673
--- Diff: docs/configuration.md ---
@@ -382,6 +382,16 @@ Apart from these, the following properties are also
available, and may be useful
</td>
</tr>
<tr>
+ <td><code>spark.kryo.registrationRequired</code></td>
+ <td>false</td>
+ <td>
+ Whether to require registration with Kryo. By default false, that is
if Kryo doesn't know
+ about a class on each access it will write out the class name with the
object. This makes the
+ output larger, but provides the most convenience. For maximum
performance, set to true and add
+ required registrations.
--- End diff --
Hey @ianoc - I found the wording here a bit confusing when reading it over.
It would be good to say the exact behavior of Kryo if this is set to true (i.e.
will it throw an exception if an unregistered class is found?). Also, the
`this` in the third sentence, it's a bit ambigugous whether that refers to the
registration itself or the default setting of this value. A slight re-word
would be :
```
Whether to require registration with Kryo. If set to 'true', Kryo will
throw an exception
if an unregistered class is serialized. If set to false (the default), Kryo
will write
unregistered class names along with each object. Writing class names can
cause
significant performance overhead, so enabling this option can enforce
strictly that a
user has not omitted classes from registration.
```
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