12.153. Release 0.94
- ORC Memory Usage
- General Changes

12.153. Release 0.94

ORC Memory Usage

This release contains additional changes to the Presto ORC reader to favorsmall buffers when reading varchar and varbinary data. Some ORC files containcolumns of data that are hundreds of megabytes compressed. When reading thesecolumns, Presto would allocate a single buffer for the compressed column data,and this would cause heap fragmentation in CMS and G1 and eventually OOMs.In this release, the hive.orc.max-buffer-size sets the maximum size for asingle ORC buffer, and for larger columns we instead stream the data. Thisreduces heap fragmentation and excessive buffers in ORC at the expense ofHDFS IOPS. The default value is 8MB.

General Changes

Update Hive CDH 4 connector to CDH 4.7.1
Fix ORDER BY with LIMIT 0
Fix compilation of try_cast
Group threads into Java thread groups to ease debugging
Add task.min-drivers config to help limit number of concurrent readers