Hive connector#

Overview#

The Hive connector allows querying data stored in an Apache Hive data warehouse. Hive is a combination of three components:

Data files in varying formats, that are typically stored in the Hadoop Distributed File System (HDFS) or in object storage systems such as Amazon S3.
Metadata about how the data files are mapped to schemas and tables. This metadata is stored in a database, such as MySQL, and is accessed via the Hive metastore service.
A query language called HiveQL. This query language is executed on a distributed computing framework such as MapReduce or Tez.

Trino only uses the first two components: the data and the metadata. It does not use HiveQL or any part of Hive’s execution environment.

Requirements#

The Hive connector requires a Hive metastore service (HMS), or a compatible implementation of the Hive metastore, such as AWS Glue Data Catalog.

Apache Hadoop 2.x and 3.x are supported, along with derivative distributions, including Cloudera CDH 5 and Hortonworks Data Platform (HDP).

Many distributed storage systems including HDFS, Amazon S3 or S3-compatible systems, Google Cloud Storage, and Azure Storage can be queried with the Hive connector.

The coordinator and all workers must have network access to the Hive metastore and the storage system. Hive metastore access with the Thrift protocol defaults to using port 9083.

Supported file types#

The following file types are supported for the Hive connector:

ORC
Parquet
Avro
RCText (RCFile using ColumnarSerDe)
RCBinary (RCFile using LazyBinaryColumnarSerDe)
SequenceFile
JSON (using org.apache.hive.hcatalog.data.JsonSerDe)
CSV (using org.apache.hadoop.hive.serde2.OpenCSVSerde)
TextFile

Metastore configuration for Avro#

In order to enable first-class support for Avro tables when using Hive 3.x, you need to add the following property definition to the Hive metastore configuration file hive-site.xml (and restart the metastore service):

<property>
     <!-- https://community.hortonworks.com/content/supportkb/247055/errorjavalangunsupportedoperationexception-storage.html -->
     <name>metastore.storage.schema.reader.impl</name>
     <value>org.apache.hadoop.hive.metastore.SerDeStorageSchemaReader</value>
 </property>

Materialized views#

The Hive connector supports reading from Hive materialized views. In Trino, these views are presented as regular, read-only tables.

Hive views#

Hive views are defined in HiveQL and stored in the Hive Metastore Service. They are analyzed to allow read access to the data.

The Hive connector includes support for reading Hive views with three different modes.

Disabled
Legacy
Experimental

You can configure the behavior in your catalog properties file.

Disabled

The default behavior is to ignore Hive views. This means that your business logic and data encoded in the views is not available in Trino.

Legacy

A very simple implementation to execute Hive views, and therefore allow read access to the data in Trino, can be enabled with hive.translate-hive-views=true and hive.legacy-hive-view-translation=true.

For temporary usage of the legacy behavior for a specific catalog, you can set the legacy_hive_view_translation catalog session property to true.

This legacy behavior interprets any HiveQL query that defines a view as if it is written in SQL. It does not do any translation, but instead relies on the fact that HiveQL is very similar to SQL.

This works for very simple Hive views, but can lead to problems for more complex queries. For example, if a HiveQL function has an identical signature but different behaviors to the SQL version, the returned results may differ. In more extreme cases the queries might fail, or not even be able to be parsed and executed.

Experimental

The new behavior is better engineered and has the potential to become a lot more powerful than the legacy implementation. It can analyze, process, and rewrite Hive views and contained expressions and statements.

It supports the following Hive view functionality:

UNION [DISTINCT] and UNION ALL against Hive views
Nested GROUP BY clauses
current_user()
LATERAL VIEW OUTER EXPLODE
LATERAL VIEW [OUTER] EXPLODE on array of struct
LATERAL VIEW json_tuple

You can enable the experimental behavior with hive.translate-hive-views=true. Remove the hive.legacy-hive-view-translation property or set it to false to make sure legacy is not enabled.

Keep in mind that numerous features are not yet implemented when experimenting with this feature. The following is an incomplete list of missing functionality:

HiveQL current_date, current_timestamp, and others
Hive function calls including translate(), window functions, and others
Common table expressions and simple case expressions
Honor timestamp precision setting
Support all Hive data types and correct mapping to Trino types
Ability to process custom UDFs

Configuration#

Create etc/catalog/hive.properties with the following contents to mount the hive connector as the hive catalog, replacing example.net:9083 with the correct host and port for your Hive metastore Thrift service:

connector.name=hive
hive.metastore.uri=thrift://example.net:9083

Multiple Hive clusters#

You can have as many catalogs as you need, so if you have additional Hive clusters, simply add another properties file to etc/catalog with a different name, making sure it ends in .properties. For example, if you name the property file sales.properties, Trino creates a catalog named sales using the configured connector.

HDFS configuration#

For basic setups, Trino configures the HDFS client automatically and does not require any configuration files. In some cases, such as when using federated HDFS or NameNode high availability, it is necessary to specify additional HDFS client options in order to access your HDFS cluster. To do so, add the hive.config.resources property to reference your HDFS config files:

hive.config.resources=/etc/hadoop/conf/core-site.xml,/etc/hadoop/conf/hdfs-site.xml

Only specify additional configuration files if necessary for your setup. We recommend reducing the configuration files to have the minimum set of required properties, as additional properties may cause problems.

The configuration files must exist on all Trino nodes. If you are referencing existing Hadoop config files, make sure to copy them to any Trino nodes that are not running Hadoop.

HDFS username and permissions#

Before running any CREATE TABLE or CREATE TABLE AS statements for Hive tables in Trino, you need to check that the user Trino is using to access HDFS has access to the Hive warehouse directory. The Hive warehouse directory is specified by the configuration variable hive.metastore.warehouse.dir in hive-site.xml, and the default value is /user/hive/warehouse.

When not using Kerberos with HDFS, Trino accesses HDFS using the OS user of the Trino process. For example, if Trino is running as nobody, it accesses HDFS as nobody. You can override this username by setting the HADOOP_USER_NAME system property in the Trino JVM config, replacing hdfs_user with the appropriate username:

-DHADOOP_USER_NAME=hdfs_user

The hive user generally works, since Hive is often started with the hive user and this user has access to the Hive warehouse.

Whenever you change the user Trino is using to access HDFS, remove /tmp/presto-* on HDFS, as the new user may not have access to the existing temporary directories.

Accessing Hadoop clusters protected with Kerberos authentication#

Kerberos authentication is supported for both HDFS and the Hive metastore. However, Kerberos authentication by ticket cache is not yet supported.

The properties that apply to Hive connector security are listed in the Hive Configuration Properties table. Please see the Hive connector security configuration section for a more detailed discussion of the security options in the Hive connector.

Hive configuration properties#

Property Name	Description	Default
`hive.config.resources`	An optional comma-separated list of HDFS configuration files. These files must exist on the machines running Trino. Only specify this if absolutely necessary to access HDFS. Example: `/etc/hdfs-site.xml`
`hive.recursive-directories`	Enable reading data from subdirectories of table or partition locations. If disabled, subdirectories are ignored. This is equivalent to the `hive.mapred.supports.subdirectories` property in Hive.	`false`
`hive.ignore-absent-partitions`	Ignore partitions when the file system location does not exist rather than failing the query. This skips data that may be expected to be part of the table.	`false`
`hive.storage-format`	The default file format used when creating new tables.	`ORC`
`hive.compression-codec`	The compression codec to use when writing files. Possible values are `NONE`, `SNAPPY`, `LZ4`, `ZSTD`, or `GZIP`.	`GZIP`
`hive.force-local-scheduling`	Force splits to be scheduled on the same node as the Hadoop DataNode process serving the split data. This is useful for installations where Trino is collocated with every DataNode.	`false`
`hive.respect-table-format`	Should new partitions be written using the existing table format or the default Trino format?	`true`
`hive.immutable-partitions`	Can new data be inserted into existing partitions? If `true` then setting `hive.insert-existing-partitions-behavior` to `APPEND` is not allowed. This also affects the `insert_existing_partitions_behavior` session property in the same way.	`false`
`hive.insert-existing-partitions-behavior`	What happens when data is inserted into an existing partition? Possible values are `APPEND` - appends data to existing partitions `OVERWRITE` - overwrites existing partitions `ERROR` - modifying existing partitions is not allowed	`APPEND`
`hive.target-max-file-size`	Best effort maximum size of new files.	`1GB`
`hive.create-empty-bucket-files`	Should empty files be created for buckets that have no data?	`false`
`hive.max-partitions-per-writers`	Maximum number of partitions per writer.	100
`hive.max-partitions-per-scan`	Maximum number of partitions for a single table scan.	100,000
`hive.hdfs.authentication.type`	HDFS authentication type. Possible values are `NONE` or `KERBEROS`.	`NONE`
`hive.hdfs.impersonation.enabled`	Enable HDFS end user impersonation.	`false`
`hive.hdfs.trino.principal`	The Kerberos principal that Trino will use when connecting to HDFS.
`hive.hdfs.trino.keytab`	HDFS client keytab location.
`hive.dfs.replication`	Hadoop file system replication factor.
`hive.security`	See Hive connector security configuration.
`security.config-file`	Path of config file to use when `hive.security=file`. See File based authorization for details.
`hive.non-managed-table-writes-enabled`	Enable writes to non-managed (external) Hive tables.	`false`
`hive.non-managed-table-creates-enabled`	Enable creating non-managed (external) Hive tables.	`true`
`hive.collect-column-statistics-on-write`	Enables automatic column level statistics collection on write. See Table Statistics for details.	`true`
`hive.s3select-pushdown.enabled`	Enable query pushdown to AWS S3 Select service.	`false`
`hive.s3select-pushdown.max-connections`	Maximum number of simultaneously open connections to S3 for S3 Select pushdown.	500
`hive.file-status-cache-tables`	Cache directory listing for specific tables. Examples: `fruit.apple,fruit.orange` to cache listings only for tables `apple` and `orange` in schema `fruit` `fruit.,vegetable.` to cache listings for all tables in schemas `fruit` and `vegetable` `*` to cache listings for all tables in all schemas
`hive.file-status-cache-size`	Maximum total number of cached file status entries.	1,000,000
`hive.file-status-cache-expire-time`	How long a cached directory listing should be considered valid.	`1m`
`hive.rcfile.time-zone`	Adjusts binary encoded timestamp values to a specific time zone. For Hive 3.1+, this should be set to UTC.	JVM default
`hive.timestamp-precision`	Specifies the precision to use for Hive columns of type `timestamp`. Possible values are `MILLISECONDS`, `MICROSECONDS` and `NANOSECONDS`. Values with higher precision than configured are rounded.	`MILLISECONDS`
`hive.temporary-staging-directory-enabled`	Controls whether the temporary staging directory configured at `hive.temporary-staging-directory-path` should be used for write operations. Temporary staging directory is never used for writes to non-sorted tables on S3, encrypted HDFS or external location. Writes to sorted tables will utilize this path for staging temporary files during sorting operation. When disabled, the target storage will be used for staging while writing sorted tables which can be inefficient when writing to object stores like S3.	`true`
`hive.temporary-staging-directory-path`	Controls the location of temporary staging directory that is used for write operations. The `${USER}` placeholder can be used to use a different location for each user.	`/tmp/presto-${USER}`
`hive.translate-hive-views`	Enable translation for Hive views.	`false`
`hive.legacy-hive-view-translation`	Use the legacy algorithm to translate Hive views. You can use the `legacy_hive_view_translation` catalog session property for temporary, catalog specific use.	`false`
`hive.parallel-partitioned-bucketed-writes`	Improve parallelism of partitioned and bucketed table writes. When disabled, the number of writing threads is limited to number of buckets.	`true`
`hive.fs.new-directory-permissions`	Controls the permissions set on new directories created for tables. It must be either ‘skip’ or an octal number, with a leading 0. If set to ‘skip’, permissions of newly created directories will not be set by Trino.	`0777`
`hive.query-partition-filter-required`	Set to `true` to force a query to use a partition filter. You can use the `query_partition_filter_required` catalog session property for temporary, catalog specific use.	`false`

ORC format configuration properties#

The following properties are used to configure the read and write operations with ORC files performed by the Hive connector.

ORC format configuration properties#
Property Name	Description	Default
`hive.orc.time-zone`	Sets the default time zone for legacy ORC files that did not declare a time zone.	JVM default
`hive.orc.use-column-names`	Access ORC columns by name. By default, columns in ORC files are accessed by their ordinal position in the Hive table definition. The equivalent catalog session property is `orc_use_column_names`.	`false`

Parquet format configuration properties#

The following properties are used to configure the read and write operations with Parquet files performed by the Hive connector.

Parquet format configuration properties#
Property Name	Description	Default
`hive.parquet.time-zone`	Adjusts timestamp values to a specific time zone. For Hive 3.1+, set this to UTC.	JVM default
`hive.parquet.use-columns-names`	Access Parquet columns by name by default. Set this property to `false` to access columns by their ordinal position in the Hive table definition. The equivalent catalog session property is `parquet_use_column_names`.	`true`

Metastore configuration properties#

The required Hive metastore can be configured with a number of properties. Specific properties can be used to further configure the Thrift or Glue metastore.

Property Name	Description
`hive.metastore`	The type of Hive metastore to use. Trino currently supports the default Hive Thrift metastore (`thrift`), and the AWS Glue Catalog (`glue`) as metadata sources. Default is `thrift`.
`hive.metastore-cache-ttl`	Duration how long cached metastore data should be considered valid. Default is `0s`.
`hive.metastore-cache-maximum-size`	Maximum number of metastore data objects in the Hive metastore cache. Default is `10000`.
`hive.metastore-refresh-interval`	Asynchronously refresh cached metastore data after access if it is older than this but is not yet expired, allowing subsequent accesses to see fresh data.
`hive.metastore-refresh-max-threads`	Maximum threads used to refresh cached metastore data. Default is `10`.
`hive.metastore-timeout`	Timeout for Hive metastore requests. Default is `10s`.
`hive.hide-delta-lake-tables`	Controls whether to hide Delta Lake tables in table listings. Currently applies only when using the AWS Glue metastore. Default is `false`.

Thrift metastore configuration properties#

Property Name	Description
`hive.metastore.uri`	The URIs of the Hive metastore to connect to using the Thrift protocol. If a comma-separated list of URIs is provided, the first URI is used by default, and the rest of the URIs are fallback metastores. This property is required. Example: `thrift://192.0.2.3:9083` or `thrift://192.0.2.3:9083,thrift://192.0.2.4:9083`
`hive.metastore.username`	The username Trino uses to access the Hive metastore.
`hive.metastore.authentication.type`	Hive metastore authentication type. Possible values are `NONE` or `KERBEROS`. Default is `NONE`.
`hive.metastore.thrift.impersonation.enabled`	Enable Hive metastore end user impersonation.
`hive.metastore.thrift.delegation-token.cache-ttl`	Time to live delegation token cache for metastore. Default is `1h`.
`hive.metastore.thrift.delegation-token.cache-maximum-size`	Delegation token cache maximum size. Default is `1000`.
`hive.metastore.thrift.client.ssl.enabled`	Use SSL when connecting to metastore. Default is `false`.
`hive.metastore.thrift.client.ssl.key`	Path to private key and client certificate (key store).
`hive.metastore.thrift.client.ssl.key-password`	Password for the private key.
`hive.metastore.thrift.client.ssl.trust-certificate`	Path to the server certificate chain (trust store). Required when SSL is enabled.
`hive.metastore.thrift.client.ssl.trust-certificate-password`	Password for the trust store
`hive.metastore.service.principal`	The Kerberos principal of the Hive metastore service.
`hive.metastore.client.principal`	The Kerberos principal that Trino uses when connecting to the Hive metastore service.
`hive.metastore.client.keytab`	Hive metastore client keytab location.

AWS Glue catalog configuration properties#

In order to use a Glue catalog, ensure to configure the metastore with hive.metastore=glue and provide further details with the following properties:

Property Name	Description
`hive.metastore.glue.region`	AWS region of the Glue Catalog. This is required when not running in EC2, or when the catalog is in a different region. Example: `us-east-1`
`hive.metastore.glue.endpoint-url`	Glue API endpoint URL (optional). Example: `https://glue.us-east-1.amazonaws.com`
`hive.metastore.glue.pin-client-to-current-region`	Pin Glue requests to the same region as the EC2 instance where Trino is running, defaults to `false`.
`hive.metastore.glue.max-connections`	Max number of concurrent connections to Glue, defaults to `5`.
`hive.metastore.glue.max-error-retries`	Maximum number of error retries for the Glue client, defaults to `10`.
`hive.metastore.glue.default-warehouse-dir`	Default warehouse directory for schemas created without an explicit `location` property.
`hive.metastore.glue.aws-credentials-provider`	Fully qualified name of the Java class to use for obtaining AWS credentials. Can be used to supply a custom credentials provider.
`hive.metastore.glue.aws-access-key`	AWS access key to use to connect to the Glue Catalog. If specified along with `hive.metastore.glue.aws-secret-key`, this parameter takes precedence over `hive.metastore.glue.iam-role`.
`hive.metastore.glue.aws-secret-key`	AWS secret key to use to connect to the Glue Catalog. If specified along with `hive.metastore.glue.aws-access-key`, this parameter takes precedence over `hive.metastore.glue.iam-role`.
`hive.metastore.glue.catalogid`	The ID of the Glue Catalog in which the metadata database resides.
`hive.metastore.glue.iam-role`	ARN of an IAM role to assume when connecting to the Glue Catalog.
`hive.metastore.glue.external-id`	External ID for the IAM role trust policy when connecting to the Glue Catalog.
`hive.metastore.glue.partitions-segments`	Number of segments for partitioned Glue tables, defaults to `5`.
`hive.metastore.glue.get-partition-threads`	Number of threads for parallel partition fetches from Glue, defaults to `20`.
`hive.metastore.glue.read-statistics-threads`	Number of threads for parallel statistic fetches from Glue, defaults to `5`.
`hive.metastore.glue.write-statistics-threads`	Number of threads for parallel statistic writes to Glue, defaults to `5`.

Google Cloud Storage configuration#

The Hive connector can access data stored in GCS, using the gs:// URI prefix. Please refer to the Hive connector GCS tutorial for step-by-step instructions.

GCS configuration properties#

Property Name	Description
`hive.gcs.json-key-file-path`	JSON key file used to authenticate with Google Cloud Storage.
`hive.gcs.use-access-token`	Use client-provided OAuth token to access Google Cloud Storage. This is mutually exclusive with a global JSON key file.

Performance tuning configuration properties#

The following table describes performance tuning properties for the Hive connector.

Warning

Performance tuning configuration properties are considered expert-level features. Altering these properties from their default values is likely to cause instability and performance degradation.

Property name	Description	Default value
`hive.max-outstanding-splits`	The target number of buffered splits for each table scan in a query, before the scheduler tries to pause.	`1000`
`hive.max-splits-per-second`	The maximum number of splits generated per second per table scan. This can be used to reduce the load on the storage system. By default, there is no limit, which results in Presto maximizing the parallelization of data access.
`hive.max-initial-splits`	For each table scan, the coordinator first assigns file sections of up to `max-initial-split-size`. After `max-initial-splits` have been assigned, `max-split-size` is used for the remaining splits.	`200`
`hive.max-initial-split-size`	The size of a single file section assigned to a worker until `max-initial-splits` have been assigned. Smaller splits results in more parallelism, which gives a boost to smaller queries.	`32 MB`
`hive.max-split-size`	The largest size of a single file section assigned to a worker. Smaller splits result in more parallelism and thus can decrease latency, but also have more overhead and increase load on the system.	`64 MB`

SQL support#

The connector provides read access and write access to data and metadata in the configured object storage system and metadata stores. In addition to the globally available and read operation statements, the connector supports the following features:

Write operations:
- Data management, see also Data management
- Schema and table management
- Views management
Security operations, see also SQL standard based authorization
Transactions

Refer to the migration guide for practical advice on migrating from Hive to Trino.

ALTER TABLE EXECUTE#

The connector supports the following commands for use with ALTER TABLE EXECUTE:

optimize: collapse files in a non-transactional table up to a threshold defined in the file_size_threshold parameter. For example, the following statement collapses files in a table that are under 10 megabytes in size:
```
ALTER TABLE test_table EXECUTE optimize(file_size_threshold => '10MB')
```
You can use a WHERE clause with the columns used to partition the table, to filter which partitions are optimized.

The optimize procedure is disabled by default, and can be enabled for a catalog with the <catalog-name>.non_transactional_optimize_enabled session property:
```
SET SESSION <catalog_name>.non_transactional_optimize_enabled=true
```

Warning

Because Hive tables are non-transactional, take note of the following possible outcomes:

If queries are run against tables that are currently being optimized, duplicate rows may be read.
In rare cases where exceptions occur during the optimize operation, a manual cleanup of the table directory is needed. In this situation, refer to the Trino logs and query failure messages to see which files need to be deleted.

Data management#

The Data management functionality includes support for INSERT, UPDATE, and DELETE statements, with the exact support depending on the storage system, file format, and metastore:

When connecting to a Hive metastore version 3.x, the Hive connector supports reading from and writing to insert-only and ACID tables, with full support for partitioning and bucketing.

DELETE applied to non-transactional tables is only supported if the table is partitioned and the WHERE clause matches entire partitions. Transactional Hive tables with ORC format support “row-by-row” deletion, in which the WHERE clause may match arbitrary sets of rows.

UPDATE is only supported for transactional Hive tables with format ORC. UPDATE of partition or bucket columns is not supported.

ACID tables created with Hive Streaming Ingest are not supported.

Table statistics#

The Hive connector supports collecting and managing table statistics to improve query processing performance.

When writing data, the Hive connector always collects basic statistics (numFiles, numRows, rawDataSize, totalSize) and by default will also collect column level statistics:

Column Type	Collectible Statistics
`TINYINT`	number of nulls, number of distinct values, min/max values
`SMALLINT`	number of nulls, number of distinct values, min/max values
`INTEGER`	number of nulls, number of distinct values, min/max values
`BIGINT`	number of nulls, number of distinct values, min/max values
`DOUBLE`	number of nulls, number of distinct values, min/max values
`REAL`	number of nulls, number of distinct values, min/max values
`DECIMAL`	number of nulls, number of distinct values, min/max values
`DATE`	number of nulls, number of distinct values, min/max values
`TIMESTAMP`	number of nulls, number of distinct values, min/max values
`VARCHAR`	number of nulls, number of distinct values
`CHAR`	number of nulls, number of distinct values
`VARBINARY`	number of nulls
`BOOLEAN`	number of nulls, number of true/false values

Updating table and partition statistics#

If your queries are complex and include joining large data sets, running ANALYZE on tables/partitions may improve query performance by collecting statistical information about the data.

When analyzing a partitioned table, the partitions to analyze can be specified via the optional partitions property, which is an array containing the values of the partition keys in the order they are declared in the table schema:

ANALYZE table_name WITH (
    partitions = ARRAY[
        ARRAY['p1_value1', 'p1_value2'],
        ARRAY['p2_value1', 'p2_value2']])

This query will collect statistics for two partitions with keys p1_value1, p1_value2 and p2_value1, p2_value2.

On wide tables, collecting statistics for all columns can be expensive and can have a detrimental effect on query planning. It is also typically unnecessary - statistics are only useful on specific columns, like join keys, predicates, grouping keys. One can specify a subset of columns to be analyzed via the optional columns property:

ANALYZE table_name WITH (
    partitions = ARRAY[ARRAY['p2_value1', 'p2_value2']],
    columns = ARRAY['col_1', 'col_2'])

This query collects statistics for columns col_1 and col_2 for the partition with keys p2_value1, p2_value2.

Note that if statistics were previously collected for all columns, they need to be dropped before re-analyzing just a subset:

CALL system.drop_stats('schema_name', 'table_name')

You can also drop statistics for selected partitions only:

CALL system.drop_stats(
    schema_name => 'schema',
    table_name => 'table',
    partition_values => ARRAY[ARRAY['p2_value1', 'p2_value2']])

Dynamic filtering#

The Hive connector supports the dynamic filtering optimization. Dynamic partition pruning is supported for partitioned tables stored in any file format for broadcast as well as partitioned joins. Dynamic bucket pruning is supported for bucketed tables stored in any file format for broadcast joins only.

For tables stored in ORC or Parquet file format, dynamic filters are also pushed into local table scan on worker nodes for broadcast joins. Dynamic filter predicates pushed into the ORC and Parquet readers are used to perform stripe or row-group pruning and save on disk I/O. Sorting the data within ORC or Parquet files by the columns used in join criteria significantly improves the effectiveness of stripe or row-group pruning. This is because grouping similar data within the same stripe or row-group greatly improves the selectivity of the min/max indexes maintained at stripe or row-group level.

Delaying execution for dynamic filters#

It can often be beneficial to wait for the collection of dynamic filters before starting a table scan. This extra wait time can potentially result in significant overall savings in query and CPU time, if dynamic filtering is able to reduce the amount of scanned data.

For the Hive connector, a table scan can be delayed for a configured amount of time until the collection of dynamic filters by using the configuration property hive.dynamic-filtering.wait-timeout in the catalog file or the catalog session property <hive-catalog>.dynamic_filtering_wait_timeout.

Schema evolution#

Hive allows the partitions in a table to have a different schema than the table. This occurs when the column types of a table are changed after partitions already exist (that use the original column types). The Hive connector supports this by allowing the same conversions as Hive:

varchar to and from tinyint, smallint, integer and bigint
real to double
Widening conversions for integers, such as tinyint to smallint

Any conversion failure results in null, which is the same behavior as Hive. For example, converting the string 'foo' to a number, or converting the string '1234' to a tinyint (which has a maximum value of 127).

Avro schema evolution#

Trino supports querying and manipulating Hive tables with the Avro storage format, which has the schema set based on an Avro schema file/literal. Trino is also capable of creating the tables in Trino by infering the schema from a valid Avro schema file located locally, or remotely in HDFS/Web server.

To specify that the Avro schema should be used for interpreting table’s data one must use avro_schema_url table property. The schema can be placed remotely in HDFS (e.g. avro_schema_url = 'hdfs://user/avro/schema/avro_data.avsc'), S3 (e.g. avro_schema_url = 's3n:///schema_bucket/schema/avro_data.avsc'), a web server (e.g. avro_schema_url = 'http://example.org/schema/avro_data.avsc') as well as local file system. This URL, where the schema is located, must be accessible from the Hive metastore and Trino coordinator/worker nodes.

The table created in Trino using avro_schema_url behaves the same way as a Hive table with avro.schema.url or avro.schema.literal set.

Example:

CREATE TABLE hive.avro.avro_data (
   id bigint
 )
WITH (
   format = 'AVRO',
   avro_schema_url = '/usr/local/avro_data.avsc'
)

The columns listed in the DDL (id in the above example) is ignored if avro_schema_url is specified. The table schema matches the schema in the Avro schema file. Before any read operation, the Avro schema is accessed so the query result reflects any changes in schema. Thus Trino takes advantage of Avro’s backward compatibility abilities.

If the schema of the table changes in the Avro schema file, the new schema can still be used to read old data. Newly added/renamed fields must have a default value in the Avro schema file.

The schema evolution behavior is as follows:

Column added in new schema: Data created with an older schema produces a default value when table is using the new schema.
Column removed in new schema: Data created with an older schema no longer outputs the data from the column that was removed.
Column is renamed in the new schema: This is equivalent to removing the column and adding a new one, and data created with an older schema produces a default value when table is using the new schema.
Changing type of column in the new schema: If the type coercion is supported by Avro or the Hive connector, then the conversion happens. An error is thrown for incompatible types.

Limitations#

The following operations are not supported when avro_schema_url is set:

CREATE TABLE AS is not supported.
Bucketing(bucketed_by) columns are not supported in CREATE TABLE.
ALTER TABLE commands modifying columns are not supported.

Procedures#

system.create_empty_partition(schema_name, table_name, partition_columns, partition_values)

Create an empty partition in the specified table.
system.sync_partition_metadata(schema_name, table_name, mode, case_sensitive)

Check and update partitions list in metastore. There are three modes available:
- ADD : add any partitions that exist on the file system, but not in the metastore.
- DROP: drop any partitions that exist in the metastore, but not on the file system.
- FULL: perform both ADD and DROP.
The case_sensitive argument is optional. The default value is true for compatibility with Hive’s MSCK REPAIR TABLE behavior, which expects the partition column names in file system paths to use lowercase (e.g. col_x=SomeValue). Partitions on the file system not conforming to this convention are ignored, unless the argument is set to false.
system.drop_stats(schema_name, table_name, partition_values)

Drops statistics for a subset of partitions or the entire table. The partitions are specified as an array whose elements are arrays of partition values (similar to the partition_values argument in create_empty_partition). If partition_values argument is omitted, stats are dropped for the entire table.

system.register_partition(schema_name, table_name, partition_columns, partition_values, location)

Registers existing location as a new partition in the metastore for the specified table.

When the location argument is omitted, the partition location is constructed using partition_columns and partition_values.

Due to security reasons, the procedure is enabled only when hive.allow-register-partition-procedure is set to true.

system.unregister_partition(schema_name, table_name, partition_columns, partition_values)

Unregisters given, existing partition in the metastore for the specified table. The partition data is not deleted.
system.flush_metadata_cache()

Flush Hive metadata caches.

Special columns#

In addition to the defined columns, the Hive connector automatically exposes metadata in a number of hidden columns in each table:

$bucket: Bucket number for this row
$path: Full file system path name of the file for this row
$file_modified_time: Date and time of the last modification of the file for this row
$file_size: Size of the file for this row
$partition: Partition name for this row

You can use these columns in your SQL statements like any other column. They can be selected directly, or used in conditional statements. For example, you can inspect the file size, location and partition for each record:

SELECT *, "$path", "$file_size", "$partition"
FROM hive.web.page_views;

Retrieve all records that belong to files stored in the partition ds=2016-08-09/country=US:

SELECT *, "$path", "$file_size"
FROM hive.web.page_views
WHERE "$partition" = 'ds=2016-08-09/country=US'

Special tables#

Table properties#

The raw Hive table properties are available as a hidden table, containing a separate column per table property, with a single row containing the property values. The properties table name is the same as the table name with $properties appended.

You can inspect the property names and values with a simple query:

SELECT * FROM hive.web."page_views$properties";

Examples#

The Hive connector supports querying and manipulating Hive tables and schemas (databases). While some uncommon operations need to be performed using Hive directly, most operations can be performed using Trino.

Create a new Hive schema named web that stores tables in an S3 bucket named my-bucket:

CREATE SCHEMA hive.web
WITH (location = 's3://my-bucket/')

Create a new Hive table named page_views in the web schema that is stored using the ORC file format, partitioned by date and country, and bucketed by user into 50 buckets. Note that Hive requires the partition columns to be the last columns in the table:

CREATE TABLE hive.web.page_views (
  view_time timestamp,
  user_id bigint,
  page_url varchar,
  ds date,
  country varchar
)
WITH (
  format = 'ORC',
  partitioned_by = ARRAY['ds', 'country'],
  bucketed_by = ARRAY['user_id'],
  bucket_count = 50
)

Drop a partition from the page_views table:

DELETE FROM hive.web.page_views
WHERE ds = DATE '2016-08-09'
  AND country = 'US'

Add an empty partition to the page_views table:

CALL system.create_empty_partition(
    schema_name => 'web',
    table_name => 'page_views',
    partition_columns => ARRAY['ds', 'country'],
    partition_values => ARRAY['2016-08-09', 'US']);

Drop stats for a partition of the page_views table:

CALL system.drop_stats(
    schema_name => 'web',
    table_name => 'page_views',
    partition_values => ARRAY['2016-08-09', 'US']);

Query the page_views table:

SELECT * FROM hive.web.page_views

List the partitions of the page_views table:

SELECT * FROM hive.web."page_views$partitions"

Create an external Hive table named request_logs that points at existing data in S3:

CREATE TABLE hive.web.request_logs (
  request_time timestamp,
  url varchar,
  ip varchar,
  user_agent varchar
)
WITH (
  format = 'TEXTFILE',
  external_location = 's3://my-bucket/data/logs/'
)

Collect statistics for the request_logs table:

ANALYZE hive.web.request_logs;

The examples shown here should work on Google Cloud Storage after replacing s3:// with gs://.

Cleaning up#

Drop the external table request_logs. This only drops the metadata for the table. The referenced data directory is not deleted:

DROP TABLE hive.web.request_logs

Drop a schema:

DROP SCHEMA hive.web

For security reasons, the sys system catalog is not accessible.
Hive’s timestamp with local zone data type is not supported. It is possible to read from a table with a column of this type, but the column data is not accessible. Writing to such a table is not supported.
Due to Hive issues HIVE-21002 and HIVE-22167, Trino does not correctly read timestamp values from Parquet, RCBinary, or Avro file formats created by Hive 3.1 or later. When reading from these file formats, Trino returns different results than Hive.
CREATE TABLE AS can be used to create transactional tables in ORC format like this:
```
CREATE TABLE <name>
WITH (
    format='ORC',
    transactional=true
)
AS <query>
```
Trino does not support gathering table statistics for Hive transactional tables. You need to use Hive to gather table statistics with ANALYZE TABLE COMPUTE STATISTICS after table creation.