Table utility commands

Delta tables support a number of utility commands.

For many Delta Lake operations, you enable integration with Apache Spark DataSourceV2 and Catalog APIs (since 3.0) by setting configurations when you create a new SparkSession. See Configure SparkSession.

In this article:

Remove files no longer referenced by a Delta table
Retrieve Delta table history
- History schema
- Operation metrics keys
Retrieve Delta table details
- Detail schema
Generate a manifest file
Convert a Parquet table to a Delta table
Convert a Delta table to a Parquet table

Remove files no longer referenced by a Delta table

You can remove files no longer referenced by a Delta table and are older than the retention threshold by running the vacuum command on the table. vacuum is not triggered automatically. The default retention threshold for the files is 7 days.

Important

vacuum deletes only data files, not log files. Log files are deleted automatically and asynchronously after checkpoint operations. The default retention period of log files is 30 days, configurable through the delta.logRetentionDuration property which you set with the ALTER TABLE SET TBLPROPERTIES SQL method. See Table properties.
The ability to time travel back to a version older than the retention period is lost after running vacuum.

VACUUM eventsTable   -- vacuum files not required by versions older than the default retention period

VACUUM '/data/events' -- vacuum files in path-based table

VACUUM delta.`/data/events/`

VACUUM delta.`/data/events/` RETAIN 100 HOURS  -- vacuum files not required by versions more than 100 hours old

VACUUM eventsTable DRY RUN    -- do dry run to get the list of files to be deleted

See Configure SparkSession for the steps to enable support for SQL commands.

from delta.tables import *

deltaTable = DeltaTable.forPath(spark, pathToTable)  # path-based tables, or
deltaTable = DeltaTable.forName(spark, tableName)    # Hive metastore-based tables

deltaTable.vacuum()        # vacuum files not required by versions older than the default retention period

deltaTable.vacuum(100)     # vacuum files not required by versions more than 100 hours old

import io.delta.tables._

val deltaTable = DeltaTable.forPath(spark, pathToTable)

deltaTable.vacuum()        // vacuum files not required by versions older than the default retention period

deltaTable.vacuum(100)     // vacuum files not required by versions more than 100 hours old

import io.delta.tables.*;
import org.apache.spark.sql.functions;

DeltaTable deltaTable = DeltaTable.forPath(spark, pathToTable);

deltaTable.vacuum();        // vacuum files not required by versions older than the default retention period

deltaTable.vacuum(100);     // vacuum files not required by versions more than 100 hours old

Note

When using VACUUM, to configure Spark to delete files in parallel (based on the number of shuffle partitions) set the session configuration "spark.databricks.delta.vacuum.parallelDelete.enabled" to "true" .

See the Delta Lake API reference for Scala, Java, and Python syntax details.

Warning

We do not recommend that you set a retention interval shorter than 7 days, because old snapshots and uncommitted files can still be in use by concurrent readers or writers to the table. If vacuum cleans up active files, concurrent readers can fail or, worse, tables can be corrupted when vacuum deletes files that have not yet been committed.

Delta Lake has a safety check to prevent you from running a dangerous vacuum command. If you are certain that there are no operations being performed on this table that take longer than the retention interval you plan to specify, you can turn off this safety check by setting the Apache Spark configuration property spark.databricks.delta.retentionDurationCheck.enabled to false. You must choose an interval that is longer than the longest running concurrent transaction and the longest period that any stream can lag behind the most recent update to the table.

Retrieve Delta table history

You can retrieve information on the operations, user, timestamp, and so on for each write to a Delta table by running the history command. The operations are returned in reverse chronological order. By default table history is retained for 30 days.

DESCRIBE HISTORY '/data/events/'          -- get the full history of the table

DESCRIBE HISTORY delta.`/data/events/`

DESCRIBE HISTORY '/data/events/' LIMIT 1  -- get the last operation only

DESCRIBE HISTORY eventsTable

See Configure SparkSession for the steps to enable support for SQL commands in Apache Spark.

from delta.tables import *

deltaTable = DeltaTable.forPath(spark, pathToTable)

fullHistoryDF = deltaTable.history()    # get the full history of the table

lastOperationDF = deltaTable.history(1) # get the last operation

import io.delta.tables._

val deltaTable = DeltaTable.forPath(spark, pathToTable)

val fullHistoryDF = deltaTable.history()    // get the full history of the table

val lastOperationDF = deltaTable.history(1) // get the last operation

import io.delta.tables.*;

DeltaTable deltaTable = DeltaTable.forPath(spark, pathToTable);

DataFrame fullHistoryDF = deltaTable.history();       // get the full history of the table

DataFrame lastOperationDF = deltaTable.history(1);    // fetch the last operation on the DeltaTable

See the Delta Lake API reference for Scala/Java/Python syntax details.

History schema

The output of the history operation has the following columns.

Column	Type	Description
version	long	Table version generated by the operation.
timestamp	timestamp	When this version was committed.
userId	string	ID of the user that ran the operation.
userName	string	Name of the user that ran the operation.
operation	string	Name of the operation.
operationParameters	map	Parameters of the operation (for example, predicates.)
job	struct	Details of the job that ran the operation.
notebook	struct	Details of notebook from which the operation was run.
clusterId	string	ID of the cluster on which the operation ran.
readVersion	long	Version of the table that was read to perform the write operation.
isolationLevel	string	Isolation level used for this operation.
isBlindAppend	boolean	Whether this operation appended data.
operationMetrics	map	Metrics of the operation (for example, number of rows and files modified.)
userMetadata	string	User-defined commit metadata if it was specified

+-------+-------------------+------+--------+---------+--------------------+----+--------+---------+-----------+--------------+-------------+--------------------+
|version|          timestamp|userId|userName|operation| operationParameters| job|notebook|clusterId|readVersion|isolationLevel|isBlindAppend|    operationMetrics|
+-------+-------------------+------+--------+---------+--------------------+----+--------+---------+-----------+--------------+-------------+--------------------+
|      5|2019-07-29 14:07:47|  null|    null|   DELETE|[predicate -> ["(...|null|    null|     null|          4|  Serializable|        false|[numTotalRows -> ...|
|      4|2019-07-29 14:07:41|  null|    null|   UPDATE|[predicate -> (id...|null|    null|     null|          3|  Serializable|        false|[numTotalRows -> ...|
|      3|2019-07-29 14:07:29|  null|    null|   DELETE|[predicate -> ["(...|null|    null|     null|          2|  Serializable|        false|[numTotalRows -> ...|
|      2|2019-07-29 14:06:56|  null|    null|   UPDATE|[predicate -> (id...|null|    null|     null|          1|  Serializable|        false|[numTotalRows -> ...|
|      1|2019-07-29 14:04:31|  null|    null|   DELETE|[predicate -> ["(...|null|    null|     null|          0|  Serializable|        false|[numTotalRows -> ...|
|      0|2019-07-29 14:01:40|  null|    null|    WRITE|[mode -> ErrorIfE...|null|    null|     null|       null|  Serializable|         true|[numFiles -> 2, n...|
+-------+-------------------+------+--------+---------+--------------------+----+--------+---------+-----------+--------------+-------------+--------------------+

Note

Some of the columns may be nulls because the corresponding information may not be available in your environment.
Columns added in the future will always be added after the last column.

Operation metrics keys

The history operation returns a collection of operations metrics in the operationMetrics column map.

The following table lists the map key definitions by operation.

Operation	Metric name	Description
WRITE, CREATE TABLE AS SELECT, REPLACE TABLE AS SELECT, COPY INTO
	numFiles	Number of files written.
	numOutputBytes	Size in bytes of the written contents.
	numOutputRows	Number of rows written.
STREAMING UPDATE
	numAddedFiles	Number of files added.
	numRemovedFiles	Number of files removed.
	numOutputRows	Number of rows written.
	numOutputBytes	Size of write in bytes.
DELETE
	numAddedFiles	Number of files added. Not provided when partitions of the table are deleted.
	numRemovedFiles	Number of files removed.
	numDeletedRows	Number of rows removed. Not provided when partitions of the table are deleted.
	numCopiedRows	Number of rows copied in the process of deleting files.
	executionTimeMs	Time taken to execute the entire operation.
	scanTimeMs	Time taken to scan the files for matches.
	rewriteTimeMs	Time taken to rewrite the matched files.
TRUNCATE
	numRemovedFiles	Number of files removed.
	executionTimeMs	Time taken to execute the entire operation.
MERGE
	numSourceRows	Number of rows in the source DataFrame.
	numTargetRowsInserted	Number of rows inserted into the target table.
	numTargetRowsUpdated	Number of rows updated in the target table.
	numTargetRowsDeleted	Number of rows deleted in the target table.
	numTargetRowsCopied	Number of target rows copied.
	numOutputRows	Total number of rows written out.
	numTargetFilesAdded	Number of files added to the sink(target).
	numTargetFilesRemoved	Number of files removed from the sink(target).
	executionTimeMs	Time taken to execute the entire operation.
	scanTimeMs	Time taken to scan the files for matches.
	rewriteTimeMs	Time taken to rewrite the matched files.
UPDATE
	numAddedFiles	Number of files added.
	numRemovedFiles	Number of files removed.
	numUpdatedRows	Number of rows updated.
	numCopiedRows	Number of rows just copied over in the process of updating files.
	executionTimeMs	Time taken to execute the entire operation.
	scanTimeMs	Time taken to scan the files for matches.
	rewriteTimeMs	Time taken to rewrite the matched files.
FSCK	numRemovedFiles	Number of files removed.
CONVERT	numConvertedFiles	Number of Parquet files that have been converted.

Retrieve Delta table details

You can retrieve detailed information about a Delta table (for example, number of files, data size) using DESCRIBE DETAIL.

DESCRIBE DETAIL '/data/events/'

DESCRIBE DETAIL eventsTable

See Configure SparkSession for the steps to enable support for SQL commands in Apache Spark.

Detail schema

The output of this operation has only one row with the following schema.

Column	Type	Description
format	string	Format of the table, that is, “delta”.
id	string	Unique ID of the table.
name	string	Name of the table as defined in the metastore.
description	string	Description of the table.
location	string	Location of the table.
createdAt	timestamp	When the table was created.
lastModified	timestamp	When the table was last modified.
partitionColumns	array of strings	Names of the partition columns if the table is partitioned.
numFiles	long	Number of the files in the latest version of the table.
properties	string-string map	All the properties set for this table.
minReaderVersion	int	Minimum version of readers (according to the log protocol) that can read the table.
minWriterVersion	int	Minimum version of writers (according to the log protocol) that can write to the table.

+------+--------------------+------------------+-----------+--------------------+--------------------+-------------------+----------------+--------+-----------+----------+----------------+----------------+
|format|                  id|              name|description|            location|           createdAt|       lastModified|partitionColumns|numFiles|sizeInBytes|properties|minReaderVersion|minWriterVersion|
+------+--------------------+------------------+-----------+--------------------+--------------------+-------------------+----------------+--------+-----------+----------+----------------+----------------+
| delta|d31f82d2-a69f-42e...|default.deltatable|       null|file:/Users/tdas/...|2020-06-05 12:20:...|2020-06-05 12:20:20|              []|      10|      12345|        []|               1|               2|
+------+--------------------+------------------+-----------+--------------------+--------------------+-------------------+----------------+--------+-----------+----------+----------------+----------------+

Generate a manifest file

You can a generate manifest file for a Delta table that can be used by other processing engines (that is, other than Apache Spark) to read the Delta table. For example, to generate a manifest file that can be used by Presto and Athena to read a Delta table, you run the following:

GENERATE symlink_format_manifest FOR TABLE delta.`<path-to-delta-table>`

See Configure SparkSession for the steps to enable support for SQL commands in Apache Spark.

deltaTable = DeltaTable.forPath(<path-to-delta-table>)
deltaTable.generate("symlink_format_manifest")

val deltaTable = DeltaTable.forPath(<path-to-delta-table>)
deltaTable.generate("symlink_format_manifest")

DeltaTable deltaTable = DeltaTable.forPath(<path-to-delta-table>);
deltaTable.generate("symlink_format_manifest");

Convert a Parquet table to a Delta table

Convert a Parquet table to a Delta table in-place. This command lists all the files in the directory, creates a Delta Lake transaction log that tracks these files, and automatically infers the data schema by reading the footers of all Parquet files. If your data is partitioned, you must specify the schema of the partition columns as a DDL-formatted string (that is, <column-name1> <type>, <column-name2> <type>, ...).

Note

If a Parquet table was created by Structured Streaming, the listing of files can be avoided by using the _spark_metadata sub-directory as the source of truth for files contained in the table setting the SQL configuration spark.databricks.delta.convert.useMetadataLog to true.

-- Convert unpartitioned Parquet table at path '<path-to-table>'
CONVERT TO DELTA parquet.`<path-to-table>`

-- Convert partitioned Parquet table at path '<path-to-table>' and partitioned by integer columns named 'part' and 'part2'
CONVERT TO DELTA parquet.`<path-to-table>` PARTITIONED BY (part int, part2 int)

See Configure SparkSession for the steps to enable support for SQL commands in Apache Spark.

from delta.tables import *

# Convert unpartitioned Parquet table at path '<path-to-table>'
deltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`")

# Convert partitioned parquet table at path '<path-to-table>' and partitioned by integer column named 'part'
partitionedDeltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`", "part int")

import io.delta.tables._

// Convert unpartitioned Parquet table at path '<path-to-table>'
val deltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`")

// Convert partitioned Parquet table at path '<path-to-table>' and partitioned by integer columns named 'part' and 'part2'
val partitionedDeltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`", "part int, part2 int")

import io.delta.tables.*;

// Convert unpartitioned Parquet table at path '<path-to-table>'
DeltaTable deltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`");

// Convert partitioned Parquet table at path '<path-to-table>' and partitioned by integer columns named 'part' and 'part2'
DeltaTable deltaTable = DeltaTable.convertToDelta(spark, "parquet.`<path-to-table>`", "part int, part2 int");

Note

Any file not tracked by Delta Lake is invisible and can be deleted when you run vacuum. You should avoid updating or appending data files during the conversion process. After the table is converted, make sure all writes go through Delta Lake.

Convert a Delta table to a Parquet table

You can easily convert a Delta table back to a Parquet table using the following steps:

If you have performed Delta Lake operations that can change the data files (for example, delete or merge), run vacuum with retention of 0 hours to delete all data files that do not belong to the latest version of the table.
Delete the _delta_log directory in the table directory.