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Jul 1, 1997 · During the American Revolution, the lake was a headwater stream for the Mohawk River and did not exist as a lake until 1908, when the state began to build a reservoir to provide water to the Barge Canal and to avoid spring flooding in the city of Rome.
- The Method of Forming and Relieving Several Guards in and About The Encampment of a Battalion
By Eric Chetwynd — 2 nd Mass. Regt.. The following article...
- Some in Rags and Some in Jags,’ But None ‘In Velvet Gowns.’ Insights on Clothing Worn by Female Followers of The Armies During The American War for Independence
Lester J. Cappon, ed., Atlas of Early American History, The...
- The Method of Forming and Relieving Several Guards in and About The Encampment of a Battalion
May 6, 2015 · In this episode Eric guides the explorers to Delta Lake to explore the legend of the lost village of Delta that is rumored to still lie at the bottom of the Lake and uncovers a haunting discovery. Is the town still intact under the water? Does anything of the village still remain today?
Dec 1, 1994 · Delta Lake, in the Nueces-Rio Grande basin four miles north of Monte Alto and twenty-four miles northeast of McAllen in Hidalgo County (at 26°25' N, 97°56' W), was previously called Monte Alto Reservoir and has also been called Mesteñas Reservoir and Willacy Reservoir.
- Overview
- Retrieve Delta table history
- History schema
- Operation metrics keys
- What is Delta Lake time travel?
- Delta time travel syntax
- What are transaction log checkpoints?
- Configure data retention for time travel queries
- Restore a Delta table to an earlier state
- Restore metrics
Each operation that modifies a Delta Lake table creates a new table version. You can use history information to audit operations, rollback a table, or query a table at a specific point in time using time travel.
You can retrieve information including the operations, user, and timestamp for each write to a Delta table by running the history command. The operations are returned in reverse chronological order.
Table history retention is determined by the table setting delta.logRetentionDuration, which is 30 days by default.
For Spark SQL syntax details, see DESCRIBE HISTORY.
See the Delta Lake API documentation for Scala/Java/Python syntax details.
The output of the history operation has the following columns.
Note
The history operation returns a collection of operations metrics in the operationMetrics column map.
The following tables list the map key definitions by operation.
Delta Lake time travel supports querying previous table versions based on timestamp or table version (as recorded in the transaction log). You can use time travel for applications such as the following:
•Re-creating analyses, reports, or outputs (for example, the output of a machine learning model). This could be useful for debugging or auditing, especially in regulated industries.
•Writing complex temporal queries.
•Fixing mistakes in your data.
•Providing snapshot isolation for a set of queries for fast changing tables.
Important
You query a Delta table with time travel by adding a clause after the table name specification.
•timestamp_expression can be any one of:
•'2018-10-18T22:15:12.013Z', that is, a string that can be cast to a timestamp
•cast('2018-10-18 13:36:32 CEST' as timestamp)
•'2018-10-18', that is, a date string
•current_timestamp() - interval 12 hours
Delta Lake records table versions as JSON files within the _delta_log directory, which is stored alongside table data. To optimize checkpoint querying, Delta Lake aggregates table versions to Parquet checkpoint files, preventing the need to read all JSON versions of table history. Azure Databricks optimizes checkpointing frequency for data size and...
To query a previous table version, you must retain both the log and the data files for that version.
Data files are deleted when VACUUM runs against a table. Delta Lake manages log file removal automatically after checkpointing table versions.
Because most Delta tables have VACUUM run against them regularly, point-in-time queries should respect the retention threshold for VACUUM, which is 7 days by default.
In order to increase the data retention threshold for Delta tables, you must configure the following table properties:
•delta.logRetentionDuration = "interval ": controls how long the history for a table is kept. The default is interval 30 days.
•delta.deletedFileRetentionDuration = "interval ": determines the threshold VACUUM uses to remove data files no longer referenced in the current table version. The default is interval 7 days.
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.
•You can restore a cloned table.
•You must have MODIFY permission on the table being restored.
•You cannot restore a table to an older version where the data files were deleted manually or by vacuum. Restoring to this version partially is still possible if spark.sql.files.ignoreMissingFiles is set to true.
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.
Delta Lake is an open-source storage framework that enables building a format agnostic Lakehouse architecture with compute engines including Spark, PrestoDB, Flink, Trino, Hive, Snowflake, Google BigQuery, Athena, Redshift, Databricks, Azure Fabric and APIs for Scala, Java, Rust, and Python.
Feb 3, 2014 · According to records in the Margaret H. McAllen Memorial Archives of the Museum of South Texas history, it was two years and 10,000 labourers later that the land became a town site, ready to be...
People also ask
What is Delta Lake?
How does Delta Lake table history work?
How does Delta Lake time travel work?
How do I view Delta Lake table history?
Mar 26, 2024 · Live events. In the last year, Delta Lake hosted twelve live events for community members to connect, learn, and share their experiences. These events ranged from technical workshops to industry discussions, each fostering a sense of community and collaboration.
