Analysis of the blocking behaviour of schema transformations in relational database systems

Abstract

In earlier work we have extended the TPC-C benchmark with basic and complex schema transformations. This paper uses this benchmark to investigate the blocking behaviour of online schema transformations in PostgreSQL, MySQL and Oracle 11g. First we discuss experiments using the data definition language of the DBMSs, which show that all complex operations are blocking, while we have mixed results for basic transformations. Second, we look at a technique for online schema transformations by Ronström, based on triggers. Our experiments show that pt-online-schema-change for MySQL and DBMS REDEFINITION for Oracle can perform basic transformations without blocking, however, support for complex transformations is missing. To conclude, we provide a solution outline for complex non-blocking transformations.