Dynamic shard allocation adjustment

The present disclosure relates to dynamically adjusting shard allocation during parallel processing operations. One example method includes determining a target completion time for a batch data processing job of an input data set performed by a plurality of tasks, each of the plurality of tasks processing a different input shard including a different portion of the input data set; identifying a first task having an estimated completion time greater than the target completion time of the batch data processing job; and splitting the first input shard into a first split input shard and a second split input shard different from the first split input shard, the first split input shard including a first portion of the first input shard, and the second split input shard including a second portion of the first input shard different from the first portion.