code: private CompletableFuture<Iterator<Operation>> readData(Void ignored) {
          long traceId = LoggerHelpers.traceEnterWithContext(log, this.traceObjectId, "readData");
          try {
              Duration readTimeout = getReadTimeout();
              return this.dataSource
                      .read(this.state.getLastReadSequenceNumber(), this.config.getMaxItemsToReadAtOnce(), readTimeout)
                      .thenApply(result -> {
                          LoggerHelpers.traceLeave(log, this.traceObjectId, "readData", traceId);
                          return result;
                      })
                      .exceptionally(ex -> {
                          ex = Exceptions.unwrap(ex);
                          if (ex instanceof TimeoutException) {
                              // TimeoutExceptions are acceptable for Reads. In that case we just return null as opposed from
                              // killing the entire Iteration. Even if we were unable to read, we may still need to flush
                              // in this iteration or do other tasks.
                              log.debug("{}: Iteration[{}] No items were read during allotted timeout of {}ms", this.traceObjectId, this.state.getIterationId(), readTimeout.toMillis());
                              return null;
                          } else {
                              throw new CompletionException(ex);
                          }
                      });
          } catch (Throwable ex) {
              // This is for synchronous exceptions.
              Throwable realEx = Exceptions.unwrap(ex);
              if (realEx instanceof TimeoutException) {
                  logErrorHandled(realEx);
                  return CompletableFuture.completedFuture(null);
              } else {
                  return Futures.failedFuture(ex);
              }
          }
      }
docs: Reads data from the OperationLog.
  
  @return A CompletableFuture that, when complete, will indicate that the read has been performed in its entirety.