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This paper presents Oracle Database Replay, a novel approach to testing changes to the relational database management system component of an information system (software upgrades, hardware changes etc). Database Replay makes it possible to subject a test system to a real production system workload, which helps identify all potential problems before implementing the planned changes on the production system. Any interesting workload period of a production database system can be captured with minimal overhead. The captured workload can be used to drive a test system while maintaining the concurrency and load characteristics of the real production workload. Therefore, the test results using database replay can provide very high assurance in determining the impact of changes to a production system before applying these changes. This paper presents the architecture of Database Replay as well as experimental results that demonstrate its usefulness as testing methodology.

Biochemistry Residues in the pathway through a membrane transporter (biological transport/cysteine scanning mutagenesis/membrane protein structure/membrane carrier/translocation pathway) ABSTRACT The structure of solute transporters is understood largely from analysis of their amino acid sequences, and more direct information is greatly needed. Here we report work that applies cysteine scanning mutagenesis to describe structure-function relations in UhpT, a bacterial membrane transporter. By using an impermeant SH-reactive agent to probe single-cysteine variants, we show that UhpT transmem-brane segment 7 spans the membrane as an a-helix and that the central portion of this helix is exposed to both membrane surfaces, forming part of the translocation pathway through this transporter. Membrane carriers and transporters comprise a large and diverse collection of proteins with functions directed to the regulation of ion and solute flux across cell membranes (1-5). Accordingly, such proteins occupy central positions in cellular programs that range from nutrient accumulation by bacteria to

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