public synchronized CompletableFuture<AppendResult> append(MetaKeyValue kv) {
        metaCache.put(kv.getKey(), new MetadataValue(nextOffset(), kv.getValue()));
        return append0(kv).thenApply(result -> {
            tryCompaction();
            return result;
        });
    }
replayDone is used to record if the meta stream has been fully replayed.
core/src/main/scala/kafka/log/streamaspect/MetaStream.java