Section 2: 13. Delta Lake Advanced Concepts

What is the primary benefit of using Z order indexing with the OPTIMIZE command?

What does running the DESCRIBE DETAIL command after OPTIMIZE help confirm?

What happens to old data files if they are less than 7 days old when attempting to execute the VACUUM command?

What was the result of trying to execute the VACUUM command without specifying a retention period?

What feature does the removal of old data files affect?

What command is used to permanently delete a table and its data from the Lakehouse?

What was confirmed after attempting to query a table that had been deleted?

What adjustment was made during the demo to facilitate file deletion?

What feature allows Delta Lake to query previous versions of a table?

Which command is used to roll back to a previous version of a table in Delta Lake?

What does the OPTIMIZE command in Delta Lake do?

How can users specify a particular version number when querying in Delta Lake?

What does a negative version number indicate when restoring data in Delta Lake?

Why is it important to minimize the number of small files in a Delta Lake table?

Which syntax can be used as an alternative to specifying a version number in a query?

What happens to existing data files when the OPTIMIZE command is executed?

Time travel feature allows querying previous versions of tables using version numbers or timestamps.
Use the SELECT ... VERSION AS OF query to access a specific table version.
Alternatively, employ @v followed by the version number for the same effect.

If data is deleted, use the RESTORE TABLE command to rollback to a prior version.
The restoration is logged in the transaction history, preserving a trace of changes.

OPTIMIZE consolidates small data files into larger, more efficient files to enhance performance.
Z-order indexing can be applied during optimization to speed up data retrieval by clustering similar values, but may not be effective on small datasets.
After optimization, only one file references the current table version.

A VACUUM command is used to cleanup unused data files, but defaults to a retention period of 7 days to avoid accidental deletions of files still in use.
To delete files older than the retention period, a workaround may involve temporarily disabling the retention check.

After executing VACUUM with the retention period altered, unnecessary data files can be removed successfully.
Once old versions of data are deleted, attempts to query these versions will result in a "file not found" error.

Use the DROP TABLE command to permanently remove a table and its data from the Lakehouse.
Upon deletion, any attempt to query the table will result in a "table not found" message, confirming the successful deletion.