The paper focuses on a new type of interactive learning content for SQL programming - worked examples of SQL code. While worked examples are popular in learning programming, their application for learning SQL is limited. Using a novel tool for presenting interactive worked examples, Database Query Analyzer (DBQA), we performed a large-scale randomized controlled study assessing the value of worked examples as a new type of practice content in a database course. We report the results of the classroom study examining the usage and the impact of DBQA. Among other aspects, we explored the effect of textual step explanations provided by DBQA.

We present an indexing system where a database index is divided into two parts: the main index located on disk and the differential index in the main memory. Both indices are implemented as B-trees. All updates performed by active transactions are written in the differential index. Periodically, writes of committed transactions are transferred from differential index to the main index as a batch-update operation. Thus, updates falling into the same leaf of the tree can be performed simultaneously. In addition, the system offers a simple recovery scheme. After a system crash, no undo operations are needed and redo operations need only write to the main memory.

In many applications it is important to be able to insert (or delete) keys into a B-tree as a batch, instead of inserting them one by one. Moreover, it may be necessary to search the B-tree concurrently with the batch update. An example of this is a text database system supporting a newspaper house: all words (keys) of each article obtained from a news agency should be inserted at once, and, at the same time, searches for documents containing certain words should be allowed as efficiently as possible. We have designed two solutions to the problem of concurrent batch update. The first solution-implemented in our commercial text database system-optimizes the speed of the batch update, and the second solution optimizes the average search time during the batch update.