code: private CompletableFuture<Void> acknowledge(Void ignored) {
          checkRunning();
          long traceId = LoggerHelpers.traceEnterWithContext(log, this.traceObjectId, "acknowledge");
  
          long highestCommittedSeqNo = this.ackCalculator.getHighestCommittedSequenceNumber(this.processors.values());
          long ackSequenceNumber = this.dataSource.getClosestValidTruncationPoint(highestCommittedSeqNo);
          if (ackSequenceNumber > this.state.getLastTruncatedSequenceNumber()) {
              // Issue the truncation and update the state (when done).
              return this.dataSource
                      .acknowledge(ackSequenceNumber, this.config.getAckTimeout())
                      .thenRun(() -> {
                          this.state.setLastTruncatedSequenceNumber(ackSequenceNumber);
                          logStageEvent("Acknowledged", "SeqNo=" + ackSequenceNumber);
                          LoggerHelpers.traceLeave(log, this.traceObjectId, "acknowledge", traceId, ackSequenceNumber);
                      });
          } else {
              // Nothing to do.
              LoggerHelpers.traceLeave(log, this.traceObjectId, "acknowledge", traceId, Operation.NO_SEQUENCE_NUMBER);
              return CompletableFuture.completedFuture(null);
          }
      }
docs: Acknowledges operations that were flushed to storage