Section 2: 12.Advanced Delta Lake Features

Questions and Answers

What does the ZORDER BY keyword accomplish when used with the OPTIMIZE command?

It allows for data rearrangement by specified columns. (correct)

It enables the deletion of outdated data files.

It optimizes the data compression of files.

It increases the number of data files created.

How does Z Order indexing improve data reading efficiency?

It compresses data files for faster decryption.

It groups files based on their creation date.

It indexes all data files for quicker retrieval.

It reduces the number of files that must be scanned when querying. (correct)

What is the default retention period for files in Delta Lake before they can be deleted using the Vacuum command?

5 days

7 days (correct)

14 days

10 days

What happens to older versions of data files after running a vacuum on a Delta table?

They are permanently deleted and cannot be recovered. Signup and view all the answers

What must be specified to perform garbage collection on unused data files in Delta Lake?

The threshold of retention period for the files. Signup and view all the answers

What does Delta Lake use to automatically version every operation on a table?

Version numbers Signup and view all the answers

Which command is used to view the history of changes made to a Delta table?

DESCRIBE HISTORY Signup and view all the answers

What is the purpose of the OPTIMIZE command in Delta Lake?

To compress small files into larger ones Signup and view all the answers

Which keyword would you use to perform a time travel query using a specific version number?

VERSION AS OF Signup and view all the answers

What feature allows Delta Lake to roll back to a previous state after bad writes?

RESTORE TABLE Signup and view all the answers

What kind of indexing does Delta Lake support to optimize query speed?

Z-Order indexing Signup and view all the answers

Which method can you use to query an older version of the Delta table using a timestamp?

TIMESTAMP AS OF Signup and view all the answers

Why is it important to compact small files in Delta Lake?

To improve the speed of read queries Signup and view all the answers

Study Notes

Delta Lake Advanced Features

Time Travel Feature
- Automatically versioned operations provide a full audit trail of changes to the table.
- Use the command DESCRIBE HISTORY to view table history in SQL.
- Query older versions using:
  - Timestamp: SELECT ... TIMESTAMP AS OF 'date_string'
  - Version Number: SELECT ... VERSION AS OF n or @v for shorthand.
- Easily perform rollbacks with the RESTORE TABLE command to revert to a specific timestamp or version in case of errors, such as accidental deletions.
Compacting Small Files
- Improves read query performance by merging small files into larger ones.
- Trigger compaction using the OPTIMIZE command, which reduces the number of small files for better efficiency.
Z-Order Indexing
- A technique for co-locating column data to optimize storage and retrieval.
- Implement Z-order indexing with ZORDER BY during the OPTIMIZE command for specified columns.
- Enhances data skipping, allowing the system to bypass irrelevant files when querying based on indexed columns.
Garbage Collection of Unused Data
- Manage unused files such as uncommitted or outdated files with the VACUUM command.
- Specify a threshold retention period (default is 7 days) to remove files older than this threshold.
- After vacuuming, cannot perform time travel to versions older than the specified retention period, as those data files will have been deleted.
Final Note
- These features optimize Delta Lake’s functionality, providing efficient data management and recovery options.

Description

This quiz explores the advanced features of Delta Lake, including time travel capabilities, table optimization via file compacting and indexing, and cleanup of unused data files. Understand how these features enhance data management and maintain an audit trail for table operations.