External tables cannot be made ACID tables since the changes on external tables are beyond the control of the compactor ( HIVE-13175). Tables in the same system not using transactions and ACID do not need to be bucketed. Tables must be bucketed to make use of these features.
See the Configuration section below for a discussion of which values need to be set to configure it. By default transactions are configured to be off.The feature has been built such that transactions can be used by any storage format that can determine how updates or deletes apply to base records (basically, that has an explicit or implicit row id), but so far the integration work has only been done for ORC. Only ORC file format is supported in this first release.The plan is to support these in a future release. BEGIN, COMMIT, and ROLLBACK are not yet supported.Bulk updates using SQL MERGE statement.Starting with Hive 0.14 these use cases can be supported via INSERT, UPDATE, and DELETE. Or a user may be contractually required to remove their customer’s data upon termination of their relationship. Or business rules may require that certain transactions be restated due to subsequent transactions (e.g., after making a purchase a customer may purchase a membership and thus be entitled to discount prices, including on the previous purchase).
#ACID PROPERTIES SQL FULL#
Or the first instance of the data may be an approximation (90% of servers reporting) with the full data provided later. Sometimes collected data is found to be incorrect and needs correction. Starting with 0.14, Hive is able to support this. These changes lead to inserts of individual records or updates of records (depending on the strategy chosen). For example, a retailer will open new stores, which need to be added to the stores table, or an existing store may change its square footage or some other tracked characteristic. In a typical star schema data warehouse, dimensions tables change slowly over time. With this new functionality this use case will be supported while allowing readers to get a consistent view of the data and avoiding too many files. These tools could stream data into existing partitions, but this would cause readers to get dirty reads (that is, they would see data written after they had started their queries) and leave many small files in their directories that would put pressure on the NameNode. Adding partitions more often leads quickly to an overwhelming number of partitions in the table. While these tools can write data at rates of hundreds or more rows per second, Hive can only add partitions every fifteen minutes to an hour. Many users have tools such as Apache Flume, Apache Storm, or Apache Kafka that they use to stream data into their Hadoop cluster. Transactions with ACID semantics have been added to Hive to address the following use cases: With the addition of transactions in Hive 0.13 it is now possible to provide full ACID semantics at the row level, so that one application can add rows while another reads from the same partition without interfering with each other. Isolation could be provided by turning on one of the available locking mechanisms ( ZooKeeper or in memory). Up until Hive 0.13, atomicity, consistency, and durability were provided at the partition level. These traits have long been expected of database systems as part of their transaction functionality. What is ACID and why should you use it?ĪCID stands for four traits of database transactions: Atomicity (an operation either succeeds completely or fails, it does not leave partial data), Consistency (once an application performs an operation the results of that operation are visible to it in every subsequent operation), Isolation (an incomplete operation by one user does not cause unexpected side effects for other users), and Durability (once an operation is complete it will be preserved even in the face of machine or system failure). No more update/delete/merge may happen on this partition until after Hive is upgraded to Hive 3.
More precisely, any partition which has had any update/delete/merge statements executed on it since the last Major Compaction, has to undergo another Major Compaction. Any transactional tables created by a Hive version prior to Hive 3 require Major Compaction to be run on every partition before upgrading to 3.0.
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