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

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. To change this behavior, see Data retention.

Important

  • vacuum removes all files from directories not managed by Delta Lake, ignoring directories beginning with _. If you are storing additional metadata like Structured Streaming checkpoints within a Delta table directory, use a directory name such as _checkpoints.

  • 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 APIs for Scala, Java, and Python syntax details.

Warning

It is recommended that you set a retention interval to be at least 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. 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.

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 Spark configuration property spark.databricks.delta.retentionDurationCheck.enabled to false.

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 APIs 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.

OPTIMIZE

numAddedFiles

Number of files added.

numRemovedFiles

Number of files optimized.

numAddedBytes

Number of bytes added after the table was optimized.

numRemovedBytes

Number of bytes removed.

minFileSize

Size of the smallest file after the table was optimized.

p25FileSize

Size of the 25th percentile file after the table was optimized.

p50FileSize

Median file size after the table was optimized.

p75FileSize

Size of the 75th percentile file after the table was optimized.

maxFileSize

Size of the largest file after the table was optimized.

Operation

Metric name

Description

RESTORE

tableSizeAfterRestore

Table size in bytes after restore.

numOfFilesAfterRestore

Number of files in the table after restore.

numRemovedFiles

Number of files removed by the restore operation.

numRestoredFiles

Number of files that were added as a result of the restore.

removedFilesSize

Size in bytes of files removed by the restore.

restoredFilesSize

Size in bytes of files added by the restore.

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.

sizeInBytes

int

The size of the latest snapshot of the table in bytes.

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/tuor/...|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:

  1. 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.

  2. Delete the _delta_log directory in the table directory.

Restore a Delta table to an earlier state

You can restore a Delta table to its earlier state by using the RESTORE command. A Delta table internally maintains historic versions of the table that enable it to be restored to an earlier state. A version corresponding to the earlier state or a timestamp of when the earlier state was created are supported as options by the RESTORE command.

Important

  • You can restore an already restored table.

  • Restoring a table to an older version where the data files were deleted manually or by vacuum will fail. Restoring to this version partially is still possible if spark.sql.files.ignoreMissingFiles is set to true.

  • The timestamp format for restoring to an earlier state is yyyy-MM-dd HH:mm:ss. Providing only a date(yyyy-MM-dd) string is also supported.

RESTORE TABLE db.target_table TO VERSION AS OF <version>
RESTORE TABLE delta.`/data/target/` TO TIMESTAMP AS OF <timestamp>
from delta.tables import *

deltaTable = DeltaTable.forPath(spark, <path-to-table>)  # path-based tables, or
deltaTable = DeltaTable.forName(spark, <table-name>)    # Hive metastore-based tables

deltaTable.restoreToVersion(0) # restore table to oldest version

deltaTable.restoreToTimestamp('2019-02-14') # restore to a specific timestamp
import io.delta.tables._

val deltaTable = DeltaTable.forPath(spark, <path-to-table>)
val deltaTable = DeltaTable.forName(spark, <table-name>)

deltaTable.restoreToVersion(0) // restore table to oldest version

deltaTable.restoreToTimestamp("2019-02-14") // restore to a specific timestamp
import io.delta.tables.*;

DeltaTable deltaTable = DeltaTable.forPath(spark, <path-to-table>);
DeltaTable deltaTable = DeltaTable.forName(spark, <table-name>);

deltaTable.restoreToVersion(0) // restore table to oldest version

deltaTable.restoreToTimestamp("2019-02-14") // restore to a specific timestamp

Important

Restore is considered a data-changing operation. Delta Lake log entries added by the RESTORE command contain dataChange set to true. If there is a downstream application, such as a Structured streaming job that processes the updates to a Delta Lake table, the data change log entries added by the restore operation are considered as new data updates, and processing them may result in duplicate data.

For example:

Table version

Operation

Delta log updates

Records in data change log updates

0

INSERT

AddFile(/path/to/file-1, dataChange = true)

(name = Viktor, age = 29, (name = George, age = 55)

1

INSERT

AddFile(/path/to/file-2, dataChange = true)

(name = George, age = 39)

2

OPTIMIZE

AddFile(/path/to/file-3, dataChange = false), RemoveFile(/path/to/file-1), RemoveFile(/path/to/file-2)

(No records as Optimize compaction does not change the data in the table)

3

RESTORE(version=1)

RemoveFile(/path/to/file-3), AddFile(/path/to/file-1, dataChange = true), AddFile(/path/to/file-2, dataChange = true)

(name = Viktor, age = 29), (name = George, age = 55), (name = George, age = 39)

In the preceding example, the RESTORE command results in updates that were already seen when reading the Delta table version 0 and 1. If a streaming query was reading this table, then these files will be considered as newly added data and will be processed again.

Restore metrics

RESTORE reports the following metrics as a single row DataFrame once the operation is complete:

  • table_size_after_restore: The size of the table after restoring.

  • num_of_files_after_restore: The number of files in the table after restoring.

  • num_removed_files: Number of files removed (logically deleted) from the table.

  • num_restored_files: Number of files restored due to rolling back.

  • removed_files_size: Total size in bytes of the files that are removed from the table.

  • restored_files_size: Total size in bytes of the files that are restored.

    Restore metrics example