Online update of b-trees

Abstract

Many scenarios impose a heavy update load on B-tree indexes in modern databases. A typical case is when B-trees are used for indexing all the keywords of a text field. For example upon the insertion of a new text record (e.g. a new document arrives), a barrage of new keywords has to be inserted into the index causing many random disk I/Os and interrupting the normal operation of the database. The common approach has been to collect the updates in a separate structure and then perform a batch update of the index. This update "freezes" the database. Many applications, however, require the immediate availability of the new updates without any interruption of the normal database operation. In this paper we present a novel online B-tree update method based on a new buffering data structure we introduce -Dynamic Bucket Tree (DBT). The DBT-buffer serves as a differential index for new updates. The grouping of keys in DBT-buffer is based on the longest common prefixes (LCP ) of their binary representations. The LCP is used as a measure of the locality of keys to be transferred to the main B-tree. Our online update system does not slow down concurrent user transactions or lead to degradation of search performance. Experiments confirm that our DBT buffer can be efficiently used for online updates of text fields. As such it represents an effective solution to the notorious problem of handling updates to an Inverted Index.