How does Hive automatically merge small files?

To automatically merge small files in Hive, you can use the following methods:

1. The task of merging small files is automated by Hive: using the hive.merge.smallfiles.avgsize parameter in Hive to set the threshold for the average size of small files, when the average size of small files is below this threshold, Hive will automatically merge them into larger files.
2. Utilize Hive’s Dynamic Partition feature: When creating a table, partition the data using partition fields and set the appropriate partition fields. This allows merging small files into larger ones through dynamic partitioning.
3. Utilizing Hive compression functionality can reduce the need for small file merging by storing data in a compressed format like Snappy or LZO when creating tables.
4. Utilize Hive’s merge tools: Hive offers various merge tools such as Hive-5881 and Hive-5317 which can be used to manually merge small files. These tools allow for merging small files into larger files by executing specific HiveQL statements or running corresponding scripts.

Regardless of the method used, the process of merging small files requires adjusting the configuration of Hive, such as changing the value of the hive.merge.smallfiles.avgsize parameter and setting the compression format. It is also important to choose the appropriate merging strategy based on the actual situation in order to achieve the goal of merging small files.