Texas: An Efficient, Portable Persistent Store

Abstract

Texas is a persistent storage system for C++, providing high performance while emphasizing simplicity, modularity and portability. A key component of the design is the use of pointer swizzling at page fault time, which exploits existing virtual memory features to implement large address spaces efficiently on stock hardware, with little or no change to existing compilers. Long pointers are used to implement an enormous address space, but are transparently converted to the hardware-supported pointer format when pages are loaded into virtual memory.

Runtime type descriptors and slightly modified heap allocation routines support page-wise pointer swizzling by allowing objects and their pointer fields to be identified within pages. If compiler support for runtime type identification is not available, a simple preprocessor can be used to generate type descriptors.

This address translation is largely independent of issues of data caching, sharing, and checkpointing; it employs operating systems’ existing virtual memories for caching, and a simple and flexible log-structured storage manager to improve checkpointing performance.

Pagewise virtual memory protections are also used to detect writes for logging purposes, without requiring any changes to compiled code. This may degrade checkpointing performance for small transactions with poor locality of writes, but page diffing and sub-page logging promise to keep performance competitive with finer-grained checkpointing schemes.

Texas presents a simple programming interface; an application creates persistent object by simply allocating them on the persistent heap. In addition, the implementation is relatively small, and is easy to incorporate into existing applications. The log-structured storage module easily supports advanced extensions such as compressed storage, versioning, and adaptive reorganization.