Skip to content


UnsafeRow is an InternalRow for mutable binary rows that are backed by raw memory outside JVM (instead of Java objects).

UnsafeRow supports Java's Externalizable and Kryo's KryoSerializable serialization/deserialization protocols.

Mutable Data Types

The following DataTypes are considered mutable data types:

  • BooleanType
  • ByteType
  • CalendarIntervalType
  • DateType
  • DecimalType
  • DoubleType
  • FloatType
  • IntegerType
  • LongType
  • NullType
  • ShortType
  • TimestampType
  • UserDefinedType (over a mutable data type)

Mutable data types have fixed length and can be mutated in place.

Examples (possibly all) of the data types that are not mutable:

KryoSerializable SerDe Protocol

Learn more in KryoSerializable.

Java's Externalizable SerDe Protocol

Learn more in


UnsafeRow knows its size (in bytes).

scala> println(unsafeRow.getSizeInBytes)


// Use ExpressionEncoder for simplicity
import org.apache.spark.sql.catalyst.encoders.ExpressionEncoder
val stringEncoder = ExpressionEncoder[String]
val row = stringEncoder.toRow("hello world")

import org.apache.spark.sql.catalyst.expressions.UnsafeRow
val unsafeRow = row match { case ur: UnsafeRow => ur }

scala> unsafeRow.getBytes
res0: Array[Byte] = Array(0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 16, 0, 0, 0, 104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100, 0, 0, 0, 0, 0)

scala> unsafeRow.getUTF8String(0)
res1: org.apache.spark.unsafe.types.UTF8String = hello world

Field Offsets

The fields of a data row are placed using field offsets.

Mutable Types

UnsafeRow considers a data type mutable if it is one of the following:

8-Byte Word Alignment and Three Regions

UnsafeRow is composed of three regions:

  1. Null Bit Set Bitmap Region (1 bit/field) for tracking null values
  2. Fixed-Length 8-Byte Values Region
  3. Variable-Length Data Region

UnsafeRow is always 8-byte word aligned and so their size is always a multiple of 8 bytes.

Equality and Hashing

Equality comparision and hashing of rows can be performed on raw bytes since if two rows are identical so should be their bit-wise representation. No type-specific interpretation is required.

Last update: 2021-07-05
Back to top