src/main/asciidoc/_chapters/spark.adoc

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[[spark]]
= HBase and Spark
:doctype: book
:numbered:
:toc: left
:icons: font
:experimental:

link:http://spark.apache.org/[Apache Spark] is a software framework that is used
to process data in memory in a distributed manner, and is replacing MapReduce in
many use cases.

Spark itself is out of scope of this document, please refer to the Spark site for
more information on the Spark project and subprojects. This document will focus
on 4 main interaction points between Spark and HBase. Those interaction points are:

Basic Spark::
  The ability to have an HBase Connection at any point in your Spark DAG.
Spark Streaming::
  The ability to have an HBase Connection at any point in your Spark Streaming
  application.
Spark Bulk Load::
  The ability to write directly to HBase HFiles for bulk insertion into HBase
SparkSQL/DataFrames::
  The ability to write SparkSQL that draws on tables that are represented in HBase.

The following sections will walk through examples of all these interaction points.

== Basic Spark

This section discusses Spark HBase integration at the lowest and simplest levels.
All the other interaction points are built upon the concepts that will be described
here.

At the root of all Spark and HBase integration is the HBaseContext. The HBaseContext
takes in HBase configurations and pushes them to the Spark executors. This allows
us to have an HBase Connection per Spark Executor in a static location.

For reference, Spark Executors can be on the same nodes as the Region Servers or
on different nodes there is no dependence of co-location. Think of every Spark
Executor as a multi-threaded client application. This allows any Spark Tasks
running on the executors to access the shared Connection object.

.HBaseContext Usage Example
====

This example shows how HBaseContext can be used to do a `foreachPartition` on a RDD
in Scala:

[source, scala]
----
val sc = new SparkContext("local", "test")
val config = new HBaseConfiguration()

...

val hbaseContext = new HBaseContext(sc, config)

rdd.hbaseForeachPartition(hbaseContext, (it, conn) => {
 val bufferedMutator = conn.getBufferedMutator(TableName.valueOf("t1"))
 it.foreach((putRecord) => {
. val put = new Put(putRecord._1)
. putRecord._2.foreach((putValue) => put.addColumn(putValue._1, putValue._2, putValue._3))
. bufferedMutator.mutate(put)
 })
 bufferedMutator.flush()
 bufferedMutator.close()
})
----

Here is the same example implemented in Java:

[source, java]
----
JavaSparkContext jsc = new JavaSparkContext(sparkConf);

try {
  List<byte[]> list = new ArrayList<>();
  list.add(Bytes.toBytes("1"));
  ...
  list.add(Bytes.toBytes("5"));

  JavaRDD<byte[]> rdd = jsc.parallelize(list);
  Configuration conf = HBaseConfiguration.create();

  JavaHBaseContext hbaseContext = new JavaHBaseContext(jsc, conf);

  hbaseContext.foreachPartition(rdd,
      new VoidFunction<Tuple2<Iterator<byte[]>, Connection>>() {
   public void call(Tuple2<Iterator<byte[]>, Connection> t)
        throws Exception {
    Table table = t._2().getTable(TableName.valueOf(tableName));
    BufferedMutator mutator = t._2().getBufferedMutator(TableName.valueOf(tableName));
    while (t._1().hasNext()) {
      byte[] b = t._1().next();
      Result r = table.get(new Get(b));
      if (r.getExists()) {
       mutator.mutate(new Put(b));
      }
    }

    mutator.flush();
    mutator.close();
    table.close();
   }
  });
} finally {
  jsc.stop();
}
----
====

All functionality between Spark and HBase will be supported both in Scala and in
Java, with the exception of SparkSQL which will support any language that is
supported by Spark. For the remaining of this documentation we will focus on
Scala examples for now.

The examples above illustrate how to do a foreachPartition with a connection. A
number of other Spark base functions  are supported out of the box:

// tag::spark_base_functions[]
`bulkPut`:: For massively parallel sending of puts to HBase
`bulkDelete`:: For massively parallel sending of deletes to HBase
`bulkGet`:: For massively parallel sending of gets to HBase to create a new RDD
`mapPartition`:: To do a Spark Map function with a Connection object to allow full
access to HBase
`hBaseRDD`:: To simplify a distributed scan to create a RDD
// end::spark_base_functions[]

For examples of all these functionalities, see the HBase-Spark Module.

== Spark Streaming
http://spark.apache.org/streaming/[Spark Streaming] is a micro batching stream
processing framework built on top of Spark. HBase and Spark Streaming make great
companions in that HBase can help serve the following benefits alongside Spark
Streaming.

* A place to grab reference data or profile data on the fly
* A place to store counts or aggregates in a way that supports Spark Streaming
promise of _only once processing_.

The HBase-Spark module’s integration points with Spark Streaming are similar to
its normal Spark integration points, in that the following commands are possible
straight off a Spark Streaming DStream.

include::spark.adoc[tags=spark_base_functions]

.`bulkPut` Example with DStreams
====

Below is an example of bulkPut with DStreams. It is very close in feel to the RDD
bulk put.

[source, scala]
----
val sc = new SparkContext("local", "test")
val config = new HBaseConfiguration()

val hbaseContext = new HBaseContext(sc, config)
val ssc = new StreamingContext(sc, Milliseconds(200))

val rdd1 = ...
val rdd2 = ...

val queue = mutable.Queue[RDD[(Array[Byte], Array[(Array[Byte],
    Array[Byte], Array[Byte])])]]()

queue += rdd1
queue += rdd2

val dStream = ssc.queueStream(queue)

dStream.hbaseBulkPut(
  hbaseContext,
  TableName.valueOf(tableName),
  (putRecord) => {
   val put = new Put(putRecord._1)
   putRecord._2.foreach((putValue) => put.addColumn(putValue._1, putValue._2, putValue._3))
   put
  })
----

There are three inputs to the `hbaseBulkPut` function.
. The hbaseContext that carries the configuration boardcast information link us
to the HBase Connections in the executors
. The table name of the table we are putting data into
. A function that will convert a record in the DStream into an HBase Put object.
====

== Bulk Load

There are two options for bulk loading data into HBase with Spark.  There is the
basic bulk load functionality that will work for cases where your rows have
millions of columns and cases where your columns are not consolidated and
partitions before the on the map side of the Spark bulk load process.

There is also a thin record bulk load option with Spark, this second option is
designed for tables that have less then 10k columns per row.  The advantage
of this second option is higher throughput and less over all load on the Spark
shuffle operation.

Both implementations work more or less like the MapReduce bulk load process in
that a partitioner partitions the rowkeys based on region splits and
the row keys are sent to the reducers in order, so that HFiles can be written
out directly from the reduce phase.

In Spark terms, the bulk load will be implemented around a the Spark
`repartitionAndSortWithinPartitions` followed by a Spark `foreachPartition`.

First lets look at an example of using the basic bulk load functionality

.Bulk Loading Example
====

The following example shows bulk loading with Spark.

[source, scala]
----
val sc = new SparkContext("local", "test")
val config = new HBaseConfiguration()

val hbaseContext = new HBaseContext(sc, config)

val stagingFolder = ...
val rdd = sc.parallelize(Array(
      (Bytes.toBytes("1"),
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("a"), Bytes.toBytes("foo1"))),
      (Bytes.toBytes("3"),
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("b"), Bytes.toBytes("foo2.b"))), ...

rdd.hbaseBulkLoad(TableName.valueOf(tableName),
  t => {
   val rowKey = t._1
   val family:Array[Byte] = t._2(0)._1
   val qualifier = t._2(0)._2
   val value = t._2(0)._3

   val keyFamilyQualifier= new KeyFamilyQualifier(rowKey, family, qualifier)

   Seq((keyFamilyQualifier, value)).iterator
  },
  stagingFolder.getPath)

val load = new LoadIncrementalHFiles(config)
load.doBulkLoad(new Path(stagingFolder.getPath),
  conn.getAdmin, table, conn.getRegionLocator(TableName.valueOf(tableName)))
----
====

The `hbaseBulkLoad` function takes three required parameters:

. The table name of the table we intend to bulk load too

. A function that will convert a record in the RDD to a tuple key value par. With
the tuple key being a KeyFamilyQualifer object and the value being the cell value.
The KeyFamilyQualifer object will hold the RowKey, Column Family, and Column Qualifier.
The shuffle will partition on the RowKey but will sort by all three values.

. The temporary path for the HFile to be written out too

Following the Spark bulk load command,  use the HBase's LoadIncrementalHFiles object
to load the newly created HFiles into HBase.

.Additional Parameters for Bulk Loading with Spark

You can set the following attributes with additional parameter options on hbaseBulkLoad.

* Max file size of the HFiles
* A flag to exclude HFiles from compactions
* Column Family settings for compression, bloomType, blockSize, and dataBlockEncoding

.Using Additional Parameters
====

[source, scala]
----
val sc = new SparkContext("local", "test")
val config = new HBaseConfiguration()

val hbaseContext = new HBaseContext(sc, config)

val stagingFolder = ...
val rdd = sc.parallelize(Array(
      (Bytes.toBytes("1"),
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("a"), Bytes.toBytes("foo1"))),
      (Bytes.toBytes("3"),
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("b"), Bytes.toBytes("foo2.b"))), ...

val familyHBaseWriterOptions = new java.util.HashMap[Array[Byte], FamilyHFileWriteOptions]
val f1Options = new FamilyHFileWriteOptions("GZ", "ROW", 128, "PREFIX")

familyHBaseWriterOptions.put(Bytes.toBytes("columnFamily1"), f1Options)

rdd.hbaseBulkLoad(TableName.valueOf(tableName),
  t => {
   val rowKey = t._1
   val family:Array[Byte] = t._2(0)._1
   val qualifier = t._2(0)._2
   val value = t._2(0)._3

   val keyFamilyQualifier= new KeyFamilyQualifier(rowKey, family, qualifier)

   Seq((keyFamilyQualifier, value)).iterator
  },
  stagingFolder.getPath,
  familyHBaseWriterOptions,
  compactionExclude = false,
  HConstants.DEFAULT_MAX_FILE_SIZE)

val load = new LoadIncrementalHFiles(config)
load.doBulkLoad(new Path(stagingFolder.getPath),
  conn.getAdmin, table, conn.getRegionLocator(TableName.valueOf(tableName)))
----
====

Now lets look at how you would call the thin record bulk load implementation

.Using thin record bulk load
====

[source, scala]
----
val sc = new SparkContext("local", "test")
val config = new HBaseConfiguration()

val hbaseContext = new HBaseContext(sc, config)

val stagingFolder = ...
val rdd = sc.parallelize(Array(
      ("1",
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("a"), Bytes.toBytes("foo1"))),
      ("3",
        (Bytes.toBytes(columnFamily1), Bytes.toBytes("b"), Bytes.toBytes("foo2.b"))), ...

rdd.hbaseBulkLoadThinRows(hbaseContext,
      TableName.valueOf(tableName),
      t => {
        val rowKey = t._1

        val familyQualifiersValues = new FamiliesQualifiersValues
        t._2.foreach(f => {
          val family:Array[Byte] = f._1
          val qualifier = f._2
          val value:Array[Byte] = f._3

          familyQualifiersValues +=(family, qualifier, value)
        })
        (new ByteArrayWrapper(Bytes.toBytes(rowKey)), familyQualifiersValues)
      },
      stagingFolder.getPath,
      new java.util.HashMap[Array[Byte], FamilyHFileWriteOptions],
      compactionExclude = false,
      20)

val load = new LoadIncrementalHFiles(config)
load.doBulkLoad(new Path(stagingFolder.getPath),
  conn.getAdmin, table, conn.getRegionLocator(TableName.valueOf(tableName)))
----
====

Note that the big difference in using bulk load for thin rows is the function
returns a tuple with the first value being the row key and the second value
being an object of FamiliesQualifiersValues, which will contain all the
values for this row for all column families.

== SparkSQL/DataFrames

HBase-Spark Connector (in HBase-Spark Module) leverages
link:https://databricks.com/blog/2015/01/09/spark-sql-data-sources-api-unified-data-access-for-the-spark-platform.html[DataSource API]
(link:https://issues.apache.org/jira/browse/SPARK-3247[SPARK-3247])
introduced in Spark-1.2.0, bridges the gap between simple HBase KV store and complex
relational SQL queries and enables users to perform complex data analytical work
on top of HBase using Spark. HBase Dataframe is a standard Spark Dataframe, and is able to
interact with any other data sources such as Hive, Orc, Parquet, JSON, etc.
HBase-Spark Connector applies critical techniques such as partition pruning, column pruning,
predicate pushdown and data locality.

To use HBase-Spark connector, users need to define the Catalog for the schema mapping
between HBase and Spark tables, prepare the data and populate the HBase table,
then load HBase DataFrame. After that, users can do integrated query and access records
in HBase table with SQL query. Following illustrates the basic procedure.

=== Define catalog

[source, scala]
----
def catalog = s"""{
       |"table":{"namespace":"default", "name":"table1"},
       |"rowkey":"key",
       |"columns":{
         |"col0":{"cf":"rowkey", "col":"key", "type":"string"},
         |"col1":{"cf":"cf1", "col":"col1", "type":"boolean"},
         |"col2":{"cf":"cf2", "col":"col2", "type":"double"},
         |"col3":{"cf":"cf3", "col":"col3", "type":"float"},
         |"col4":{"cf":"cf4", "col":"col4", "type":"int"},
         |"col5":{"cf":"cf5", "col":"col5", "type":"bigint"},
         |"col6":{"cf":"cf6", "col":"col6", "type":"smallint"},
         |"col7":{"cf":"cf7", "col":"col7", "type":"string"},
         |"col8":{"cf":"cf8", "col":"col8", "type":"tinyint"}
       |}
     |}""".stripMargin
----

Catalog defines a mapping between HBase and Spark tables. There are two critical parts of this catalog.
One is the rowkey definition and the other is the mapping between table column in Spark and
the column family and column qualifier in HBase. The above defines a schema for a HBase table
with name as table1, row key as key and a number of columns (col1 `-` col8). Note that the rowkey
also has to be defined in details as a column (col0), which has a specific cf (rowkey).

=== Save the DataFrame

[source, scala]
----
case class HBaseRecord(
   col0: String,
   col1: Boolean,
   col2: Double,
   col3: Float,
   col4: Int,       
   col5: Long,
   col6: Short,
   col7: String,
   col8: Byte)

object HBaseRecord
{                                                                                                             
   def apply(i: Int, t: String): HBaseRecord = {
      val s = s"""row${"%03d".format(i)}"""       
      HBaseRecord(s,
      i % 2 == 0,
      i.toDouble,
      i.toFloat,  
      i,
      i.toLong,
      i.toShort,  
      s"String$i: $t",      
      i.toByte)
  }
}

val data = (0 to 255).map { i =>  HBaseRecord(i, "extra")}

sc.parallelize(data).toDF.write.options(
 Map(HBaseTableCatalog.tableCatalog -> catalog, HBaseTableCatalog.newTable -> "5"))
 .format("org.apache.hadoop.hbase.spark ")
 .save()

----
`data` prepared by the user is a local Scala collection which has 256 HBaseRecord objects.
`sc.parallelize(data)` function distributes `data` to form an RDD. `toDF` returns a DataFrame.
`write` function returns a DataFrameWriter used to write the DataFrame to external storage
systems (e.g. HBase here). Given a DataFrame with specified schema `catalog`, `save` function
will create an HBase table with 5 regions and save the DataFrame inside.

=== Load the DataFrame

[source, scala]
----
def withCatalog(cat: String): DataFrame = {
  sqlContext
  .read
  .options(Map(HBaseTableCatalog.tableCatalog->cat))
  .format("org.apache.hadoop.hbase.spark")
  .load()
}
val df = withCatalog(catalog)
----
In ‘withCatalog’ function, sqlContext is a variable of SQLContext, which is the entry point
for working with structured data (rows and columns) in Spark.
`read` returns a DataFrameReader that can be used to read data in as a DataFrame.
`option` function adds input options for the underlying data source to the DataFrameReader,
and `format` function specifies the input data source format for the DataFrameReader.
The `load()` function loads input in as a DataFrame. The date frame `df` returned
by `withCatalog` function could be used to access HBase table, such as 4.4 and 4.5.

=== Language Integrated Query

[source, scala]
----
val s = df.filter(($"col0" <= "row050" && $"col0" > "row040") ||
  $"col0" === "row005" ||
  $"col0" <= "row005")
  .select("col0", "col1", "col4")
s.show
----
DataFrame can do various operations, such as join, sort, select, filter, orderBy and so on.
`df.filter` above filters rows using the given SQL expression. `select` selects a set of columns:
`col0`, `col1` and `col4`.

=== SQL Query

[source, scala]
----
df.registerTempTable("table1")
sqlContext.sql("select count(col1) from table1").show
----

`registerTempTable` registers `df` DataFrame as a temporary table using the table name `table1`.
The lifetime of this temporary table is tied to the SQLContext that was used to create `df`.
`sqlContext.sql` function allows the user to execute SQL queries.

=== Others

.Query with different timestamps
====
In HBaseSparkConf, four parameters related to timestamp can be set. They are TIMESTAMP,
MIN_TIMESTAMP, MAX_TIMESTAMP and MAX_VERSIONS respectively. Users can query records with
different timestamps or time ranges with MIN_TIMESTAMP and MAX_TIMESTAMP. In the meantime,
use concrete value instead of tsSpecified and oldMs in the examples below.

The example below shows how to load df DataFrame with different timestamps.
tsSpecified is specified by the user.
HBaseTableCatalog defines the HBase and Relation relation schema.
writeCatalog defines catalog for the schema mapping.

[source, scala]
----
val df = sqlContext.read
      .options(Map(HBaseTableCatalog.tableCatalog -> writeCatalog, HBaseSparkConf.TIMESTAMP -> tsSpecified.toString))
      .format("org.apache.hadoop.hbase.spark")
      .load()
----

The example below shows how to load df DataFrame with different time ranges.
oldMs is specified by the user.

[source, scala]
----
val df = sqlContext.read
      .options(Map(HBaseTableCatalog.tableCatalog -> writeCatalog, HBaseSparkConf.MIN_TIMESTAMP -> "0",
        HBaseSparkConf.MAX_TIMESTAMP -> oldMs.toString))
      .format("org.apache.hadoop.hbase.spark")
      .load()
----
After loading df DataFrame, users can query data.

[source, scala]
----
df.registerTempTable("table")
sqlContext.sql("select count(col1) from table").show
----
====

.Native Avro support
====
HBase-Spark Connector support different data formats like Avro, Jason, etc. The use case below
shows how spark supports Avro. User can persist the Avro record into HBase directly. Internally,
the Avro schema is converted to a native Spark Catalyst data type automatically.
Note that both key-value parts in an HBase table can be defined in Avro format.

1) Define catalog for the schema mapping:

[source, scala]
----
def catalog = s"""{
                     |"table":{"namespace":"default", "name":"Avrotable"},
                      |"rowkey":"key",
                      |"columns":{
                      |"col0":{"cf":"rowkey", "col":"key", "type":"string"},
                      |"col1":{"cf":"cf1", "col":"col1", "type":"binary"}
                      |}
                      |}""".stripMargin
----

`catalog` is a schema for a HBase table named `Avrotable`. row key as key and
one column col1. The rowkey also has to be defined in details as a column (col0),
which has a specific cf (rowkey).

2) Prepare the Data:

[source, scala]
----
 object AvroHBaseRecord {
   val schemaString =
     s"""{"namespace": "example.avro",
         |   "type": "record",      "name": "User",
         |    "fields": [
         |        {"name": "name", "type": "string"},
         |        {"name": "favorite_number",  "type": ["int", "null"]},
         |        {"name": "favorite_color", "type": ["string", "null"]},
         |        {"name": "favorite_array", "type": {"type": "array", "items": "string"}},
         |        {"name": "favorite_map", "type": {"type": "map", "values": "int"}}
         |      ]    }""".stripMargin

   val avroSchema: Schema = {
     val p = new Schema.Parser
     p.parse(schemaString)
   }

   def apply(i: Int): AvroHBaseRecord = {
     val user = new GenericData.Record(avroSchema);
     user.put("name", s"name${"%03d".format(i)}")
     user.put("favorite_number", i)
     user.put("favorite_color", s"color${"%03d".format(i)}")
     val favoriteArray = new GenericData.Array[String](2, avroSchema.getField("favorite_array").schema())
     favoriteArray.add(s"number${i}")
     favoriteArray.add(s"number${i+1}")
     user.put("favorite_array", favoriteArray)
     import collection.JavaConverters._
     val favoriteMap = Map[String, Int](("key1" -> i), ("key2" -> (i+1))).asJava
     user.put("favorite_map", favoriteMap)
     val avroByte = AvroSedes.serialize(user, avroSchema)
     AvroHBaseRecord(s"name${"%03d".format(i)}", avroByte)
   }
 }

 val data = (0 to 255).map { i =>
    AvroHBaseRecord(i)
 }
----

`schemaString` is defined first, then it is parsed to get `avroSchema`. `avroSchema` is used to
generate `AvroHBaseRecord`. `data` prepared by users is a local Scala collection
which has 256 `AvroHBaseRecord` objects.

3) Save DataFrame:

[source, scala]
----
 sc.parallelize(data).toDF.write.options(
     Map(HBaseTableCatalog.tableCatalog -> catalog, HBaseTableCatalog.newTable -> "5"))
     .format("org.apache.spark.sql.execution.datasources.hbase")
     .save()
----

Given a data frame with specified schema `catalog`, above will create an HBase table with 5
regions and save the data frame inside.

4) Load the DataFrame

[source, scala]
----
def avroCatalog = s"""{
            |"table":{"namespace":"default", "name":"avrotable"},
            |"rowkey":"key",
            |"columns":{
              |"col0":{"cf":"rowkey", "col":"key", "type":"string"},
              |"col1":{"cf":"cf1", "col":"col1", "avro":"avroSchema"}
            |}
          |}""".stripMargin

 def withCatalog(cat: String): DataFrame = {
     sqlContext
         .read
         .options(Map("avroSchema" -> AvroHBaseRecord.schemaString, HBaseTableCatalog.tableCatalog -> avroCatalog))
         .format("org.apache.spark.sql.execution.datasources.hbase")
         .load()
 }
 val df = withCatalog(catalog)
----

In `withCatalog` function, `read` returns a DataFrameReader that can be used to read data in as a DataFrame.
The `option` function adds input options for the underlying data source to the DataFrameReader.
There are two options: one is to set `avroSchema` as `AvroHBaseRecord.schemaString`, and one is to
set `HBaseTableCatalog.tableCatalog` as `avroCatalog`. The `load()` function loads input in as a DataFrame.
The date frame `df` returned by `withCatalog` function could be used to access the HBase table.

5) SQL Query

[source, scala]
----
 df.registerTempTable("avrotable")
 val c = sqlContext.sql("select count(1) from avrotable").
----

After loading df DataFrame, users can query data. registerTempTable registers df DataFrame
as a temporary table using the table name avrotable. `sqlContext.sql` function allows the
user to execute SQL queries.
====