parquet-index

Spark SQL index for Parquet tables

Overview

Package allows to create index for Parquet tables (as datasource and persistent tables) to reduce query latency when used for almost interactive analysis or point queries in Spark SQL. It is designed for use case when table does not change frequently, but is used for queries often, e.g. using Thrift JDBC/ODBC server. When indexed, schema and list of files (including partitioning) will be automatically resolved from index metastore instead of inferring schema every time datasource is created.

Project is experimental. Any feedback, issues, or PRs are welcome.

Documentation reflects changes in master branch, for documentation on a specific version, please select corresponding version tag or branch.

Metastore

Metastore keeps information about all indexed tables and can be created on local file system or HDFS (see available options below) with support for in-memory cache of index (after first scan). Each created index includes different statistics (min/max/null) and, optionally, column filters statistics (e.g. bloom filters) on indexed columns.

Supported predicates

Index is automatically enabled for scan when provided predicate contains one or several filters with indexed columns; if no filters on indexed columns are provided, then normal scan is used, but with benefits of already resolved partitions and schema. Applying min/max statistics and column filter statistics (if available) happens after partition pruning. Statistics are kept per Parquet block metadata. Note that performance also depends on values distribution and predicate selectivity. Spark Parquet reader is used to read data.

Most of the Spark SQL predicates are supported to use statistics and/or column filter (EqualTo, In, GreaterThan, LessThan, and others). Note that predicates work best for equality or isin conditions and logical operators (And, Or, Not), e.g. $"a" === 1 && $"b" === "abc" or $"a".isin("a", "b", "c").

Supported Spark SQL types

Currently only these types are supported for indexed columns:

• IntegerType
• LongType
• StringType
• DateType
• TimestampType

Limitations

• Indexed columns must be top level primitive columns with types above
• Indexed columns cannot be the same as partitioning columns
• Append mode is not yet supported for Parquet table when creating index
• Certain Spark versions are supported (see table below)

Requirements

• Scala 2.12.x
• JDK 8+

Previous versions have support for Scala 2.11.x, Scala 2.10.x, and JDK 7, see README and build.sbt for corresponding tag or branch. See build section to compile for desired Java/Scala versions.

And, if using the Python API, Python 3.x with a working version of pyspark.

The current version parts ways with Python 2 definitely. Python 2.7 is officially deprecated, which is the reason why we opted not to write a retrocompatible wrapper around the Scala API.

Linking

The parquet-index package can be added to Spark by using the --packages command line option. For example, run this to include it when starting spark-shell (Scala 2.12.x):

 $SPARK_HOME/bin/spark-shell --packages lightcopy:parquet-index:0.5.0-s_2.12

Or for pyspark to use Python 3 API (see section below):

$SPARK_HOME/bin/pyspark --packages lightcopy:parquet-index:0.5.0-s_2.12

Options

Currently supported options, use --conf key=value on a command line to provide options similar to other Spark configuration or add them to spark-defaults.conf file.

Example

Scala API

Most of the API is defined in DataFrameIndexManager. Usage is similar to Spark's DataFrameReader, but for spark.index. See example below on different commands (runnable in spark-shell).

// Start spark-shell and create dummy table "codes.parquet", use repartition
// to create more or less generic situation with value distribution
spark.range(0, 1000000).
  select($"id", $"id".cast("string").as("code"), lit("xyz").as("name")).
  repartition(400).
  write.partitionBy("name").parquet("temp/codes.parquet")

import com.github.lightcopy.implicits._
// Create index for table, this will create index files in index_metastore,
// you can configure different options - see table above

// All Spark SQL modes are available ('append', 'overwrite', 'ignore', 'error')
// You can also use `.indexByAll` to choose all columns in schema that
// can be indexed
spark.index.create.
  mode("overwrite").indexBy($"id", $"code").parquet("temp/codes.parquet")

// Check if index for table exists, should return "true"
spark.index.exists.parquet("temp/codes.parquet")

// Query table using index, should return 1 record, and will scan only small
// number of files (1 file usually if filter statistics are enabled). This
// example uses filters on both columns, though any filters can be used,
// e.g. only on id or code
// Metastore will cache index catalog to reduce time for subsequent calls
spark.index.parquet("temp/codes.parquet").
  filter($"id" === 123 && $"code" === "123").collect

// Delete index in metastore, also invalidates cache
// no-op if there is such index does not exist
// (does NOT delete original table)
spark.index.delete.parquet("temp/codes.parquet")

// You can compare performance with this
spark.read.parquet("temp/codes.parquet").
  filter($"id" === 123 && $"code" === "123").collect

Java API

To use indexing in Java create QueryContext based on SparkSession and invoke method index() to get index functionality. Example below illustrates how to use indexing in standalone application.

import com.github.lightcopy.QueryContext;

// Optionally use `config(key, value)` to specify additional index configuration
SparkSession spark = SparkSession.
  builder().
  master("local[*]").
  appName("Java example").
  getOrCreate();

// Create query context, entry point to working with parquet-index
QueryContext context = new QueryContext(spark);

// Create index by inferring columns from Parquet table
context.index().create().indexByAll().parquet("table.parquet");

// Create index by specifying index columns, you can also provide `Column` instances, e.g.
// `new Column[] { new Column("col1"), new Column("col2") }`.
// Mode can be provided as `org.apache.spark.sql.SaveMode` or String value
context.index().create().
  mode("overwrite").
  indexBy(new String[] { "col1", "col2" }).
  parquet("table.parquet");

// Check if index exists for the table
boolean exists = context.index().exists().parquet("table.parquet");

// Run query for indexed table
Dataset<Row> df = context.index().parquet("table.parquet").filter("col2 = 'c'");

// Delete index from metastore
context.index().delete().parquet("table.parquet");

Python 3.x API

Following example shows usage of Python 3 API (runnable in pyspark)

from lightcopy.index import QueryContext

# Create QueryContext from SparkSession
context = QueryContext(spark)

# Create index in metastore for Parquet table 'table.parquet' using 'col1' and 'col2' columns
context.index.create.indexBy('col1', 'col2').parquet('table.parquet')

# Create index in metastore for Parquet table 'table.parquet' using all inferred columns and
# overwrite any existing index for this table
context.index.create.mode('overwrite').indexByAll().parquet('table.parquet')

# Check if index exists, returns 'True' if exists, otherwise 'False'
context.index.exists.parquet('table.parquet')

# Query index for table, returns DataFrame
df = context.index.parquet('table.parquet').filter('col1 = 123')

# Delete index from metastore, if index does not exist - no-op
context.index.delete.parquet('table.parquet')

Persistent tables API

Package also supports index for persistent tables that are saved using saveAsTable() in Parquet format and accessible using spark.table(tableName). When using with persistent tables, just replace .parquet(path_to_the_file) with .table(table_name). API is available in Scala, Java and Python 3.

Scala

import com.github.lightcopy.implicits._

// Create index for table name that exists in Spark catalog
spark.index.create.indexBy("col1", "col2", "col3").table("table_name")

// Check if index exists for persistent table
val exists: Boolean = spark.index.exists.table("table_name")

// Query index for persistent table
val df = spark.index.table("table_name").filter("col1 > 1")

// Delete index for persistent table (does not drop table itself)
spark.index.delete.table("table_name")

Java

// Java API is very similar to Scala API
import com.github.lightcopy.QueryContext;

SparkSession spark = ...;

QueryContext context = new QueryContext(spark);

// Create index for persistent table
context.index().create().indexByAll().table("table_name");

// Check if index exists for persistent table
boolean exists = context.index().exists().table("table_name");

// Run query for indexed persistent table
Dataset<Row> df = context.index().table("table_name").filter("col2 = 'c'");

// Delete index from metastore (does not drop table)
context.index().delete().table("table_name");

Python 3

from lightcopy.index import QueryContext

context = QueryContext(spark)

# Create index from Spark persistent table
context.index.create.mode('overwrite').indexBy('col1', 'col2').table('table_name')

# Check if index exists for persistent table. 'True' if exists in metastore, 'False' otherwise
context.index.exists.table('table_name')

# Query indexed persistent table
df = context.index.table('table_name').filter('col1 = 123')

# Delete index for persistent table (does not drop table)
context.index.delete.table('table_name')

Building From Source

This library is built using sbt, to build a JAR file simply run sbt package from project root.

Testing

Run sbt test from project root. See .travis.yml for CI build matrix.