gjacoby126 commented on a change in pull request #390: HBASE-22623 - Add
RegionObserver coprocessor hook for preWALAppend
URL: https://github.com/apache/hbase/pull/390#discussion_r305577407
##########
File path:
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java
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@@ -1104,4 +1105,18 @@ default DeleteTracker postInstantiateDeleteTracker(
throws IOException {
return delTracker;
}
+
+ /**
+ * Called just before the WAL Entry is appended to the WAL. Implementing
this hook allows
+ * coprocessors to add extended attributes to the WALKey that then get
persisted to the
+ * WAL, and are available to replication endpoints to use in processing WAL
Entries.
+ * @param ctx
+ * @param key
+ * @return
+ * @throws IOException
+ */
+ default WALKeyImpl
preWALAppend(ObserverContext<RegionCoprocessorEnvironment> ctx, WALKeyImpl key)
Review comment:
@apurtell - the header comments for WALEdit state that the class is meant to
be read-only for coprocs. There are coprocessor hooks that take a WALEdit
parameter, but unless I missed one, they all seem to be _after_ the WAL has
been appended so that mutating the edit has no function.
I don't understand the reason for the restriction -- we trust coprocessor
implementers to do sane things already everywhere else -- but since the code
had an explicit policy I tried to honor it.
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