Version: 0.11.0

Schema Evolution

Schema evolution allows users to easily change the current schema of a Hudi table to adapt to the data that is changing over time. As of 0.11.0 release, Spark SQL (Spark 3.1.x, 3.2.1 and above) DDL support for Schema evolution has been added and is experimental.

Scenarios

Columns (including nested columns) can be added, deleted, modified, and moved.
Partition columns cannot be evolved.
You cannot add, delete, or perform operations on nested columns of the Array type.

SparkSQL Schema Evolution and Syntax Description

Before using schema evolution, pls set spark.sql.extensions. For Spark 3.2.1 and above, spark.sql.catalog.spark_catalog also need to be set.

# Spark SQL for spark 3.1.x
spark-sql --packages org.apache.hudi:hudi-spark3.1.2-bundle_2.12:0.11.1 \
--conf 'spark.serializer=org.apache.spark.serializer.KryoSerializer' \
--conf 'spark.sql.extensions=org.apache.spark.sql.hudi.HoodieSparkSessionExtension'

# Spark SQL for spark 3.2.1 and above
spark-sql --packages org.apache.hudi:hudi-spark3-bundle_2.12:0.11.1 \
--conf 'spark.serializer=org.apache.spark.serializer.KryoSerializer' \
--conf 'spark.sql.extensions=org.apache.spark.sql.hudi.HoodieSparkSessionExtension' \
--conf 'spark.sql.catalog.spark_catalog=org.apache.spark.sql.hudi.catalog.HoodieCatalog'

After start spark-app, pls exec set hoodie.schema.on.read.enable=true to enable schema evolution.

note

Currently, Schema evolution cannot disabled once being enabled.

tip

When use hive metastore, may encounter a problem: org.apache.hadoop.hive.ql.metadata.HiveException: Unable to alter table. The following columns have types incompatible with the existing columns in their respective positions.

Make sure disable hive.metastore.disallow.incompatible.col.type.changes in hive side.

Adding Columns

Syntax

-- add columns
ALTER TABLE tableName ADD COLUMNS(col_spec[, col_spec ...])

Parameter Description

Parameter	Description
tableName	Table name
col_spec	Column specifications, consisting of five fields, col_name, col_type, nullable, comment, and col_position.

col_name : name of the new column. It is mandatory.To add a sub-column to a nested column, specify the full name of the sub-column in this field.

For example:

To add sub-column col1 to a nested struct type column column users struct<name: string, age: int>, set this field to users.col1.
To add sub-column col1 to a nested map type column memeber map<string, struct<n: string, a: int>>, set this field to member.value.col1.

col_type : type of the new column.

nullable : whether the new column can be null. The value can be left empty. Now this field is not used in Hudi.

comment : comment of the new column. The value can be left empty.

col_position : position where the new column is added. The value can be FIRST or AFTER origin_col.

If it is set to FIRST, the new column will be added to the first column of the table.
If it is set to AFTER origin_col, the new column will be added after original column origin_col.
The value can be left empty. FIRST can be used only when new sub-columns are added to nested columns. Do not use FIRST in top-level columns. There are no restrictions about the usage of AFTER.

Examples

ALTER TABLE h0 ADD COLUMNS(ext0 string);
ALTER TABLE h0 ADD COLUMNS(new_col int not null comment 'add new column' AFTER col1);
ALTER TABLE complex_table ADD COLUMNS(col_struct.col_name string comment 'add new column to a struct col' AFTER col_from_col_struct);

Altering Columns

Syntax

-- alter table ... alter column
ALTER TABLE tableName ALTER [COLUMN] col_old_name TYPE column_type [COMMENT] col_comment[FIRST|AFTER] column_name

Parameter Description

Parameter	Description
tableName	Table name.
col_old_name	Name of the column to be altered.
column_type	Type of the target column.
col_comment	col_comment.
column_name	New position to place the target column. For example, AFTER column_name indicates that the target column is placed after column_name.

Examples

--- Changing the column type
ALTER TABLE table1 ALTER COLUMN a.b.c TYPE bigint

--- Altering other attributes
ALTER TABLE table1 ALTER COLUMN a.b.c COMMENT 'new comment'
ALTER TABLE table1 ALTER COLUMN a.b.c FIRST
ALTER TABLE table1 ALTER COLUMN a.b.c AFTER x
ALTER TABLE table1 ALTER COLUMN a.b.c DROP NOT NULL

column type change

Source\Target	long	float	double	string	decimal	date	int
int	Y	Y	Y	Y	Y	N	Y
long	Y	Y	Y	Y	Y	N	N
float	N	Y	Y	Y	Y	N	N
double	N	N	Y	Y	Y	N	N
decimal	N	N	N	Y	Y	N	N
string	N	N	N	Y	Y	Y	N
date	N	N	N	Y	N	Y	N

Deleting Columns

Syntax

-- alter table ... drop columns
ALTER TABLE tableName DROP COLUMN|COLUMNS cols

Examples

ALTER TABLE table1 DROP COLUMN a.b.c
ALTER TABLE table1 DROP COLUMNS a.b.c, x, y

Changing Column Name

Syntax

-- alter table ... rename column
ALTER TABLE tableName RENAME COLUMN old_columnName TO new_columnName

Examples

ALTER TABLE table1 RENAME COLUMN a.b.c TO x

Modifying Table Properties

Syntax

-- alter table ... set|unset
ALTER TABLE tableName SET|UNSET tblproperties

Examples

ALTER TABLE table SET TBLPROPERTIES ('table_property' = 'property_value')
ALTER TABLE table UNSET TBLPROPERTIES [IF EXISTS] ('comment', 'key')

Changing a Table Name

Syntax

-- alter table ... rename
ALTER TABLE tableName RENAME TO newTableName

Examples

ALTER TABLE table1 RENAME TO table2