rkhachatryan commented on a change in pull request #14943:
URL: https://github.com/apache/flink/pull/14943#discussion_r585567609
##########
File path:
flink-runtime/src/main/java/org/apache/flink/runtime/state/StateBackendLoader.java
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@@ -249,6 +266,66 @@ public static StateBackend
fromApplicationOrConfigOrDefault(
return backend;
}
+ /**
+ * This is the state backend loader that loads a {@link
DelegateStateBackend} wrapping the state
+ * backend loaded from {@link
StateBackendLoader#fromApplicationOrConfigOrDefault} when
+ * delegation is enabled. If delegation is not enabled, the underlying
wrapped state backend is
+ * returned instead.
+ *
+ * <p>{@link DelegateStateBackend} can only be enabled through
configuration.
+ *
+ * @param fromApplication StateBackend defined from application
+ * @param config The configuration to load the state backend from
+ * @param classLoader The class loader that should be used to load the
state backend
+ * @param logger Optionally, a logger to log actions to (may be null)
+ * @return The instantiated state backend.
+ * @throws DynamicCodeLoadingException Thrown if a state backend (factory)
is configured and the
+ * (factory) class was not found or could not be instantiated
+ * @throws IllegalConfigurationException May be thrown by the
StateBackendFactory when creating
+ * / configuring the state backend in the factory
+ * @throws IOException May be thrown by the StateBackendFactory when
instantiating the state
+ * backend
+ */
+ public static StateBackend loadStateBackend(
+ @Nullable StateBackend fromApplication,
+ Configuration config,
+ ClassLoader classLoader,
+ @Nullable Logger logger)
+ throws IllegalConfigurationException, DynamicCodeLoadingException,
IOException {
+
+ final StateBackend backend =
+ fromApplicationOrConfigOrDefault(fromApplication, config,
classLoader, logger);
+
+ if (config.get(CheckpointingOptions.ENABLE_STATE_CHANGE_LOG)) {
+ LOG.info(
+ "Delegate State Backend is used, and the root State
Backend is {}",
+ backend.getClass().getSimpleName());
+
+ // ChangelogStateBackend resides in a separate module, load it
using reflection
+ try {
+ Constructor<? extends DelegateStateBackend> constructor =
+ Class.forName(CHANGELOG_STATE_BACKEND, false,
classLoader)
+ .asSubclass(DelegateStateBackend.class)
+ .getConstructor(StateBackend.class);
+ return constructor.newInstance(backend);
Review comment:
1. It's better to not rely on distant checks (as this method can
potentially receive an argument from somewhere else; or the distant method can
change)
2. I think the check in `loadStateBackend` should be removed.
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