Index-Organized Tables and Clustered Indexes. The index-only scan executes an SQL statement using only the redundant data stored in the index.
The original data in the heap table is not needed. If we take that concept to the next level and put all columns into the index, you may wonder why we need the heap table. Some databases can indeed use an index as primary table store. The Oracle database calls this concept index-organized tables (IOT), other databases use the term clustered index. In this section, both terms are used to either put the emphasis on the table or the index characteristics as needed. An index-organized table is thus a B-tree index without a heap table. “Just the right amount of detail for the typical SQL Developer”Chandrasekar Ravoori on Amazon.co.uk (5 stars) The drawbacks of an index-organized table become apparent when creating another index on the same table. The following figures show an index lookup for finding all sales on May 23rd 2012. Figure 5.2. Figure 5.3. Important MySQL Oracle PostgreSQL SQL Server.
Hibernate Batch Processing – Why you may not be using it. (Even if you think you are) « chronicles of a java developer. Hibernate batch processing is powerful but it has many pitfalls that developers must be aware of in order to use it properly and efficiently.
Most people who use batch probably find out about it by trying to perform a large operation and finding out the hard way why batching is needed. They run out of memory. Once this is resolved they assume that batching is working properly. The problem is that even if you are flushing your first level cache, you may not be batching your SQL statements. Hibernate flushes by default for the following reasons: Before some queriesWhen commit() is executedWhen session.flush() is executed The thing to note here is that until the session is flushed, every persistent object is placed into the first level cache (your JVM's memory). To avoid this problem you need to call the flush() and then clear() method on the session at regular intervals. Assuming the Customer cascades save to the Cart object you would expect to see something like this in your SQL logs:
Introduction to Databases. About The Course A bold experiment in distributed education, "Introduction to Databases" is being offered free and online to students worldwide, October 10 - December 12, 2011. Students have access to lecture videos, are given assignments and exams, receive regular feedback on progress, and participate in a discussion forum. Those who successfully complete the course will receive a statement of accomplishment. Taught by Professor Jennifer Widom, the curriculum draws from Stanford's popular Introduction to Databases course. A high speed internet connection is recommended as the course content is based on videos and online exercises.
About The Instructor Professor Jennifer Widom is the Fletcher Jones Professor and Chair of the Computer Science Department at Stanford University. Why Learn About Databases? Databases are incredibly prevalent -- they underlie technology used by most people every day if not every hour. Course Description Frequently Asked Questions.