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carbon-as-spark-datasource-guide.md

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CarbonData as Spark's Datasource

The CarbonData fileformat is now integrated as Spark datasource for read and write operation without using CarbonSession. This is useful for users who wants to use carbondata as spark's data source.

Note: You can only apply the functions/features supported by spark datasource APIs, functionalities supported would be similar to Parquet. The carbon session features are not supported. The result is displayed as byte array format when select query on binary column in spark-sql.

Create Table with DDL

Now you can create Carbon table using Spark's datasource DDL syntax.

 CREATE [TEMPORARY] TABLE [IF NOT EXISTS] [db_name.]table_name
     [(col_name1 col_type1 [COMMENT col_comment1], ...)]
     USING CARBON
     [OPTIONS (key1=val1, key2=val2, ...)]
     [PARTITIONED BY (col_name1, col_name2, ...)]
     [CLUSTERED BY (col_name3, col_name4, ...) INTO num_buckets BUCKETS]
     [LOCATION path]
     [COMMENT table_comment]
     [TBLPROPERTIES (key1=val1, key2=val2, ...)]
     [AS select_statement]

Supported OPTIONS

Property Default Value Description
table_blocksize 1024 Size of blocks to write onto hdfs. For more details, see Table Block Size Configuration.
table_blocklet_size 64 Size of blocklet to write.
table_page_size_inmb 0 Size of each page in carbon table, if page size crosses this value before 32000 rows, page will be cut to that many rows. Helps in keep page size to fit cache size
local_dictionary_threshold 10000 Cardinality upto which the local dictionary can be generated. For more details, see Local Dictionary Configuration.
local_dictionary_enable false Enable local dictionary generation. For more details, see Local Dictionary Configuration.
sort_columns all dimensions are sorted Columns to include in sort and its order of sort. For more details, see Sort Columns Configuration.
sort_scope local_sort Sort scope of the load.Options include no sort, local sort, batch sort, and global sort. For more details, see Sort Scope Configuration.
long_string_columns null Comma separated string/char/varchar columns which are more than 32k length. For more details, see String longer than 32000 characters.

NOTE: please set long_string_columns for varchar column.

Example

 CREATE TABLE CARBON_TABLE (NAME STRING) USING CARBON OPTIONS('table_blocksize'='256')

Using DataFrame

Carbon format can be used in dataframe also. Following are the ways to use carbon format in dataframe.

Write carbon using dataframe

df.write.format("carbon").save(path)

Read carbon using dataframe

val df = spark.read.format("carbon").load(path)

Example

import org.apache.spark.sql.SparkSession

val spark = SparkSession
  .builder()
  .appName("Spark SQL basic example")
  .config("spark.some.config.option", "some-value")
  .getOrCreate()

// For implicit conversions like converting RDDs to DataFrames
import spark.implicits._
val df = spark.sparkContext.parallelize(1 to 10 * 10 * 1000)
     .map(x => (r.nextInt(100000), "name" + x % 8, "city" + x % 50, BigDecimal.apply(x % 60)))
      .toDF("ID", "name", "city", "age")
      
// Write to carbon format      
df.write.format("carbon").save("/user/person_table")

// Read carbon using dataframe
val dfread = spark.read.format("carbon").load("/user/person_table")
dfread.show()

Supported OPTIONS using dataframe

In addition to the above Supported Options, following properties are supported using dataframe.

Property Default Value Description
bucket_number NA Number of buckets to be created. For more details, see Bucketing.
bucket_columns NA Columns which are to be placed in buckets. For more details, see Bucketing.
streaming false Whether the table is a streaming table. For more details, see Streaming.
timestampformat yyyy-MM-dd HH:mm:ss For specifying the format of TIMESTAMP data type column. For more details, see TimestampFormat.
dateformat yyyy-MM-dd For specifying the format of DATE data type column. For more details, see DateFormat.
SPATIAL_INDEX NA Used to configure Spatial Index name. This name is appended to SPATIAL_INDEX in the subsequent sub-property configurations. xxx in the below sub-properties refer to index name. Generated spatial index column is not allowed in any properties except in SORT_COLUMNS table property.For more details, see Spatial Index.
SPATIAL_INDEX.xxx.type NA Type of algorithm for processing spatial data. Currently, supports 'geohash' and 'geosot'.
SPATIAL_INDEX.xxx.sourcecolumns NA longitude and latitude column names as in the table. These columns are used to generate index value for each row.
SPATIAL_INDEX.xxx.originLatitude NA Latitude of origin.
SPATIAL_INDEX.xxx.gridSize NA Grid size of raster data in metres. Currently, spatial index supports raster data.
SPATIAL_INDEX.xxx.conversionRatio NA Conversion factor. It allows user to translate longitude and latitude to long. For example, if the data to load is longitude = 13.123456, latitude = 101.12356. User can configure conversion ratio sub-property value as 1000000, and change data to load as longitude = 13123456 and latitude = 10112356. Operations on long is much faster compared to floating-point numbers.
SPATIAL_INDEX.xxx.class NA Optional user custom implementation class. Value is fully qualified class name.

Reference : list of carbon properties