public int messagesRetained() {
            return messagesRetained;
        }
Check whether a record should be retained in the log. Note that {@link #checkBatchRetention(RecordBatch)}
is used prior to checking individual record retention. Only records from batches which were not
explicitly discarded with {@link BatchRetention#DELETE} will be considered.
clients/src/main/java/org/apache/kafka/common/record/MemoryRecords.java