Mmuzaf commented on code in PR #2133:
URL: https://github.com/apache/cassandra/pull/2133#discussion_r1148129493
##########
src/java/org/apache/cassandra/db/virtual/SettingsTable.java:
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@@ -157,4 +174,85 @@ private static Map<String, String>
getBackwardsCompatableNames()
return names;
}
+
+ /**
+ * This class is used to provide backwards compatable support for the
settings table in case the {@link Config}
+ * metadata changes. This class will provide the old names for the
properties, but will use the new name to
+ * get the value from the {@link Config} object.
+ * <p>
+ * Updating a configuration property object will throw an exception if you
will try to update a deprecated property.
+ */
+ private static class BackwardsCompatableRegistry implements Registry
+ {
+ private final Registry registry;
+ private final Map<String, Replacement> replacements;
+ private final Set<String> uniquePropertyKeys;
+ public BackwardsCompatableRegistry(Registry registry)
+ {
+ this.registry = registry;
+ this.replacements = replacements(registry);
+ // Some configs kept the same name, but changed the type, so we
need to make sure we don't return the same name twice.
+ this.uniquePropertyKeys =
ImmutableSet.<String>builder().addAll(registry.keys()).addAll(replacements.keySet()).build();
+ }
+
+ @Override
+ public void set(String name, @Nullable Object value)
+ {
+ Replacement replacement = replacements.get(name);
+ if (replacement == null)
+ registry.set(name, value);
+ else
+ throw new ConfigurationException(String.format("Unable to set
'%s' as it is deprecated and is read only; use '%s' instead", name,
replacement.newName));
Review Comment:
It can't break anything because the SettingsTable is not updatable now, so
it's up to us in this patch to decide which set of properties to make updatable
:-)
AFAIU, the `Replacement` is used to support backward compatibility between
the releases so that users can use their old configs with new releases smoothly
keeping in mind that they have to migrate to a new version of the
`cassandra.yaml` (e.g. export the real config from the cluster to the yaml
file).
So showing a replaced name in the SettingsTable might be OK, but if we make
it updatable it might cause confusion - because both the replaced name and a
new name are responsible for the same single thing, and this does not lead the
user to understand which is the _right_ property in the release he uses.
If I'm missing something, just let me know and I'll fix it (it is easy).
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