public int getDefMaxMsgSize(String topicName) {
        Integer maxMsgSizeInB = topicMaxSizeInBMap.get(topicName);
        return maxMsgSizeInB == null ? defMaxMsgSize.get() : maxMsgSizeInB;
    }
The class caches the max msg size settings
 returned from the server.
inlong-tubemq/tubemq-client/src/main/java/org/apache/inlong/tubemq/client/producer/MaxMsgSizeHolder.java