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Using Kite Properties |
Kite gives you the option of changing settings of existing system properties to enhance performance. You also have the option of creating custom properties for additional control over how Kite reads or writes your data.
There are several dataset properties that affect how files are written. These settings are especially relevant for Parquet, because it buffers records in memory.
You can set properties on your datasets with DatasetDescriptor.Builder.property when using the API, or with the --set option from the Kite CLI.
kite.writer.cache-size controls the number of files kept open by an HDFS or Hive dataset writer. The default cache size is 10.
Writers open one file per partition to which they write records. When the writer receives a record that goes in a new partition (one for which there isn't an open file) it creates a new file in that partition. If the number of open files exceeds the cache size, Kite closes the file that was used least recently.
For some applications, adjusting the writer cache size can improve performance. For example, you might have an application writing a year's worth of data to year/month partitions. There are 12 partitions, but, by default, only 10 files are open at the same time. The application must constantly close and open files, which slows down your writes. If you increase the writer cache to 12, files for all 12 months are open at once. To increase the writer cache size, you can use the CLI update command.
kite-dataset update dataset:hdfs:/user/me/datasets/annual_earnings --set kite.writer.cache-size=12
Kite passes descriptor properties to the underlying file formats. For example, Parquet defines parquet.block.size, which is approximately the amount of data that is buffered before writing a group of records (a row group). parquet.block.size defaults to 128MB.
The amount of data kept in memory for each file could be up to the Parquet block size in bytes. That means that the upper bound for a writer's memory consumption is parquet.block.size multiplied by the kite.writer.cache-size. It is important that this number doesn't exceed a reasonable portion of the heap memory allocated to the process, or else the write could fail with an OutOfMemoryException.
The recommended way to avoid out of memory exceptions is to write to fewer files. When working with Crunch, you can use CrunchDatasets.partition methods to restructure data so that all of the records stored in a given partition are processed by the same writer.
In addition to setting existing system properties, you can create your own key-value pairs to use as custom properties in your application.
When using the CLI create or update commands, you add custom properties with the option --set prop.name=value.
When using the Kite API, you can add properties using DatasetDescriptor.Builder.property.