To create a new table using the Avro file format, issue the CREATE TABLE statement and any subsequent INSERT statements in the Hive shell. For information about loading data into Avro tables through Hive, see Avro page on the Hive wiki.

Once the table is created in Hive, switch back to impala-shell and issue an INVALIDATE METADATA table_name statement. Then you can run queries for that table through impala-shell. If you already have data files in Avro format, you can also issue LOAD DATA in either Impala or Hive.

hive> CREATE TABLE new_table
    > ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.avro.AvroSerDe'
    > STORED AS INPUTFORMAT 'org.apache.hadoop.hive.ql.io.avro.AvroContainerInputFormat'
    > OUTPUTFORMAT 'org.apache.hadoop.hive.ql.io.avro.AvroContainerOutputFormat'
    > TBLPROPERTIES ('avro.schema.literal'='{
    >    "name": "my_record",
    >    "type": "record",
    >    "fields": [
    >       {"name":"bool_col", "type":"boolean"},
    >       {"name":"int_col", "type":"int"},
    >       {"name":"long_col", "type":"long"},
    >       {"name":"float_col", "type":"float"},
    >       {"name":"double_col", "type":"double"},
    >       {"name":"string_col", "type":"string"},
    >       {"name": "nullable_int", "type": ["null", "int"]}]}');
OK
Time taken: 6.372 seconds

Each field of the record becomes a column of the table. Note that any other information, such as the record name, is ignored.

  Note: For nullable columns, make sure to put the "null" entry before the actual type name.

After you create an Avro table in Hive, issue an INVALIDATE METADATA the next time you connect to Impala through impala-shell. This is a one-time operation to make Impala aware of the new table. You can issue the statement while connected to any Impala node, and the catalog service broadcasts the change to all other Impala nodes.

After you load new data into an Avro table, either through a Hive LOAD DATA or INSERT statement, or by manually copying or moving files into the data directory for the table, issue a REFRESH table_name statement the next time you connect to Impala through impala-shell. You can issue the statement while connected to any Impala node, and the catalog service broadcasts the change to all other Impala nodes.

Impala only supports fields of type boolean, int, long, float, double, and string, or unions of these types with null; for example, ["string", "null"]. Unions with null essentially create a nullable type.

While you can embed a schema directly in your CREATE TABLE statement, as shown above, column width restrictions in the Hive metastore limit the length of schema you can specify. If you encounter problems with long schema literals, try storing your schema as a JSON file in HDFS instead. Specify your schema in HDFS using table properties similar to the following:

tblproperties ('avro.schema.url'='hdfs//your-name-node:port/path/to/schema.json');

To enable compression for Avro tables, specify settings in the Hive shell to enable compression and to specify a codec, then issue a CREATE TABLE statement as in the preceding examples. Impala supports the snappy and deflate codecs for Avro tables.

For example:

hive> set hive.exec.compress.output=true;
hive> set avro.output.codec=snappy;

Starting in Impala 1.1, Impala can deal with Avro data files that employ schema evolution, where different data files within the same table use slightly different type definitions. (You would perform the schema evolution operation by issuing an ALTER TABLE statement in the Hive shell.) The old and new types for any changed columns must be compatible, for example a column might start as an int and later change to a bigint or float.

As with any other tables where the definitions are changed or data is added outside of the current impalad node, ensure that Impala loads the latest metadata for the table if the Avro schema is modified through Hive. Issue a REFRESH table_name or INVALIDATE METADATA table_name statement. REFRESH reloads the metadata immediately, INVALIDATE METADATA reloads the metadata the next time the table is accessed.

When Avro data files or columns are not consulted during a query, Impala does not check for consistency. Thus, if you issue SELECT c1, c2 FROM t1, Impala does not return any error if the column c3 changed in an incompatible way. If a query retrieves data from some partitions but not others, Impala does not check the data files for the unused partitions.

In the Hive DDL statements, you can specify an avro.schema.literal table property (if the schema definition is short) or an avro.schema.url property (if the schema definition is long, or to allow convenient editing for the definition).

For example, running the following SQL code in the Hive shell creates a table using the Avro file format and puts some sample data into it:

CREATE TABLE avro_table (a string, b string)
ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.avro.AvroSerDe'
STORED AS INPUTFORMAT 'org.apache.hadoop.hive.ql.io.avro.AvroContainerInputFormat'
OUTPUTFORMAT 'org.apache.hadoop.hive.ql.io.avro.AvroContainerOutputFormat'
TBLPROPERTIES (
  'avro.schema.literal'='{
    "type": "record",
    "name": "my_record",
    "fields": [
      {"name": "a", "type": "int"},
      {"name": "b", "type": "string"}
    ]}');

INSERT OVERWRITE TABLE avro_table SELECT 1, "avro" FROM functional.alltypes LIMIT 1;

Once the Avro table is created and contains data, you can query it through the impala-shell command:

-- [localhost:21000] > select * from avro_table;
-- Query: select * from avro_table
-- Query finished, fetching results ...
-- +---+------+
-- | a | b    |
-- +---+------+
-- | 1 | avro |
-- +---+------+

Now in the Hive shell, you change the type of a column and add a new column with a default value:

-- Promote column "a" from INT to FLOAT (no need to update Avro schema)
ALTER TABLE avro_table CHANGE A A FLOAT;

-- Add column "c" with default
ALTER TABLE avro_table ADD COLUMNS (c int);
ALTER TABLE avro_table SET TBLPROPERTIES (
  'avro.schema.literal'='{
    "type": "record",
    "name": "my_record",
    "fields": [
      {"name": "a", "type": "int"},
      {"name": "b", "type": "string"},
      {"name": "c", "type": "int", "default": 10}
    ]}');

Once again in impala-shell, you can query the Avro table based on its latest schema definition. Because the table metadata was changed outside of Impala, you issue a REFRESH statement first so that Impala has up-to-date metadata for the table.

-- [localhost:21000] > refresh avro_table;
-- Query: refresh avro_table
-- Query finished, fetching results ...

-- Returned 0 row(s) in 0.23s
-- [localhost:21000] > select * from avro_table;
-- Query: select * from avro_table
-- Query finished, fetching results ...
-- +---+------+----+
-- | a | b    | c  |
-- +---+------+----+
-- | 1 | avro | 10 |
-- +---+------+----+
-- Returned 1 row(s) in 0.14s