Comet Configuration Settings

Comet provides the following configuration settings.

Config

Description

Default Value

spark.comet.batchSize

The columnar batch size, i.e., the maximum number of rows that a batch can contain.

8192

spark.comet.caseConversion.enabled

Java uses locale-specific rules when converting strings to upper or lower case and Rust does not, so we disable upper and lower by default.

false

spark.comet.cast.allowIncompatible

Comet is not currently fully compatible with Spark for all cast operations. Set this config to true to allow them anyway. See compatibility guide for more information.

false

spark.comet.columnar.shuffle.async.enabled

Whether to enable asynchronous shuffle for Arrow-based shuffle.

false

spark.comet.columnar.shuffle.async.max.thread.num

Maximum number of threads on an executor used for Comet async columnar shuffle. This is the upper bound of total number of shuffle threads per executor. In other words, if the number of cores * the number of shuffle threads per task spark.comet.columnar.shuffle.async.thread.num is larger than this config. Comet will use this config as the number of shuffle threads per executor instead.

100

spark.comet.columnar.shuffle.async.thread.num

Number of threads used for Comet async columnar shuffle per shuffle task. Note that more threads means more memory requirement to buffer shuffle data before flushing to disk. Also, more threads may not always improve performance, and should be set based on the number of cores available.

3

spark.comet.convert.csv.enabled

When enabled, data from Spark (non-native) CSV v1 and v2 scans will be converted to Arrow format. Note that to enable native vectorized execution, both this config and ‘spark.comet.exec.enabled’ need to be enabled.

false

spark.comet.convert.json.enabled

When enabled, data from Spark (non-native) JSON v1 and v2 scans will be converted to Arrow format. Note that to enable native vectorized execution, both this config and ‘spark.comet.exec.enabled’ need to be enabled.

false

spark.comet.convert.parquet.enabled

When enabled, data from Spark (non-native) Parquet v1 and v2 scans will be converted to Arrow format. Note that to enable native vectorized execution, both this config and ‘spark.comet.exec.enabled’ need to be enabled.

false

spark.comet.debug.enabled

Whether to enable debug mode for Comet. When enabled, Comet will do additional checks for debugging purpose. For example, validating array when importing arrays from JVM at native side. Note that these checks may be expensive in performance and should only be enabled for debugging purpose.

false

spark.comet.dppFallback.enabled

Whether to fall back to Spark for queries that use DPP.

true

spark.comet.enabled

Whether to enable Comet extension for Spark. When this is turned on, Spark will use Comet to read Parquet data source. Note that to enable native vectorized execution, both this config and ‘spark.comet.exec.enabled’ need to be enabled. By default, this config is the value of the env var ENABLE_COMET if set, or true otherwise.

true

spark.comet.exceptionOnDatetimeRebase

Whether to throw exception when seeing dates/timestamps from the legacy hybrid (Julian + Gregorian) calendar. Since Spark 3, dates/timestamps were written according to the Proleptic Gregorian calendar. When this is true, Comet will throw exceptions when seeing these dates/timestamps that were written by Spark version before 3.0. If this is false, these dates/timestamps will be read as if they were written to the Proleptic Gregorian calendar and will not be rebased.

false

spark.comet.exec.aggregate.enabled

Whether to enable aggregate by default.

true

spark.comet.exec.broadcastExchange.enabled

Whether to enable broadcastExchange by default.

true

spark.comet.exec.broadcastHashJoin.enabled

Whether to enable broadcastHashJoin by default.

true

spark.comet.exec.coalesce.enabled

Whether to enable coalesce by default.

true

spark.comet.exec.collectLimit.enabled

Whether to enable collectLimit by default.

true

spark.comet.exec.enabled

Whether to enable Comet native vectorized execution for Spark. This controls whether Spark should convert operators into their Comet counterparts and execute them in native space. Note: each operator is associated with a separate config in the format of ‘spark.comet.exec.<operator_name>.enabled’ at the moment, and both the config and this need to be turned on, in order for the operator to be executed in native.

true

spark.comet.exec.expand.enabled

Whether to enable expand by default.

true

spark.comet.exec.filter.enabled

Whether to enable filter by default.

true

spark.comet.exec.globalLimit.enabled

Whether to enable globalLimit by default.

true

spark.comet.exec.hashJoin.enabled

Whether to enable hashJoin by default.

true

spark.comet.exec.localLimit.enabled

Whether to enable localLimit by default.

true

spark.comet.exec.memoryFraction

The fraction of memory from Comet memory overhead that the native memory manager can use for execution. The purpose of this config is to set aside memory for untracked data structures, as well as imprecise size estimation during memory acquisition.

0.7

spark.comet.exec.project.enabled

Whether to enable project by default.

true

spark.comet.exec.replaceSortMergeJoin

Experimental feature to force Spark to replace SortMergeJoin with ShuffledHashJoin for improved performance. This feature is not stable yet. For more information, refer to the Comet Tuning Guide (https://datafusion.apache.org/comet/user-guide/tuning.html).

false

spark.comet.exec.shuffle.codec

The codec of Comet native shuffle used to compress shuffle data. Only zstd is supported.

zstd

spark.comet.exec.shuffle.enabled

Whether to enable Comet native shuffle. Note that this requires setting ‘spark.shuffle.manager’ to ‘org.apache.spark.sql.comet.execution.shuffle.CometShuffleManager’. ‘spark.shuffle.manager’ must be set before starting the Spark application and cannot be changed during the application.

true

spark.comet.exec.sort.enabled

Whether to enable sort by default.

true

spark.comet.exec.sortMergeJoin.enabled

Whether to enable sortMergeJoin by default.

true

spark.comet.exec.sortMergeJoinWithJoinFilter.enabled

Experimental support for Sort Merge Join with filter

false

spark.comet.exec.stddev.enabled

Whether to enable stddev by default. stddev is slower than Spark’s implementation.

true

spark.comet.exec.takeOrderedAndProject.enabled

Whether to enable takeOrderedAndProject by default.

true

spark.comet.exec.union.enabled

Whether to enable union by default.

true

spark.comet.exec.window.enabled

Whether to enable window by default.

true

spark.comet.explain.native.enabled

When this setting is enabled, Comet will provide a tree representation of the native query plan before execution and again after execution, with metrics.

false

spark.comet.explain.verbose.enabled

When this setting is enabled, Comet will provide a verbose tree representation of the extended information.

false

spark.comet.explainFallback.enabled

When this setting is enabled, Comet will provide logging explaining the reason(s) why a query stage cannot be executed natively. Set this to false to reduce the amount of logging.

false

spark.comet.memory.overhead.factor

Fraction of executor memory to be allocated as additional non-heap memory per executor process for Comet.

0.2

spark.comet.memory.overhead.min

Minimum amount of additional memory to be allocated per executor process for Comet, in MiB.

402653184b

spark.comet.nativeLoadRequired

Whether to require Comet native library to load successfully when Comet is enabled. If not, Comet will silently fallback to Spark when it fails to load the native lib. Otherwise, an error will be thrown and the Spark job will be aborted.

false

spark.comet.parquet.enable.directBuffer

Whether to use Java direct byte buffer when reading Parquet.

false

spark.comet.parquet.read.io.adjust.readRange.skew

In the parallel reader, if the read ranges submitted are skewed in sizes, this option will cause the reader to break up larger read ranges into smaller ranges to reduce the skew. This will result in a slightly larger number of connections opened to the file system but may give improved performance.

false

spark.comet.parquet.read.io.mergeRanges

When enabled the parallel reader will try to merge ranges of data that are separated by less than ‘comet.parquet.read.io.mergeRanges.delta’ bytes. Longer continuous reads are faster on cloud storage.

true

spark.comet.parquet.read.io.mergeRanges.delta

The delta in bytes between consecutive read ranges below which the parallel reader will try to merge the ranges. The default is 8MB.

8388608

spark.comet.parquet.read.parallel.io.enabled

Whether to enable Comet’s parallel reader for Parquet files. The parallel reader reads ranges of consecutive data in a file in parallel. It is faster for large files and row groups but uses more resources.

true

spark.comet.parquet.read.parallel.io.thread-pool.size

The maximum number of parallel threads the parallel reader will use in a single executor. For executors configured with a smaller number of cores, use a smaller number.

16

spark.comet.regexp.allowIncompatible

Comet is not currently fully compatible with Spark for all regular expressions. Set this config to true to allow them anyway using Rust’s regular expression engine. See compatibility guide for more information.

false

spark.comet.scan.enabled

Whether to enable native scans. When this is turned on, Spark will use Comet to read supported data sources (currently only Parquet is supported natively). Note that to enable native vectorized execution, both this config and ‘spark.comet.exec.enabled’ need to be enabled.

true

spark.comet.scan.preFetch.enabled

Whether to enable pre-fetching feature of CometScan.

false

spark.comet.scan.preFetch.threadNum

The number of threads running pre-fetching for CometScan. Effective if spark.comet.scan.preFetch.enabled is enabled. Note that more pre-fetching threads means more memory requirement to store pre-fetched row groups.

2

spark.comet.shuffle.preferDictionary.ratio

The ratio of total values to distinct values in a string column to decide whether to prefer dictionary encoding when shuffling the column. If the ratio is higher than this config, dictionary encoding will be used on shuffling string column. This config is effective if it is higher than 1.0. Note that this config is only used when spark.comet.exec.shuffle.mode is jvm.

10.0

spark.comet.sparkToColumnar.supportedOperatorList

A comma-separated list of operators that will be converted to Arrow columnar format when ‘spark.comet.sparkToColumnar.enabled’ is true

Range,InMemoryTableScan

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Supported Spark Expressions

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Compatibility Guide