Advanced Perl Programming

Chapter 10. Persistence

There must be at least 500,000,000 rats in the United States. Of course, I’m speaking only from memory.

—Edgar Wilson Nye

It would be an ideal world indeed if we never had to worry about fatal bugs or power failures.^[35] For now, we have to contend with the fact that the attention span of a computer is only as long as its cord and that our data is too precious to be left within the confines of electronic memory. The ability of a system or module to make an application’s data live longer than its application is called persistence.^[36]

Considering that databases amount to a multi-billion-dollar industry and that DBI (Database Interface) and associated Perl modules are next only to CGI in CPAN’s download statistics, it would not be a stretch to say that persistence is the most important of all technologies. In this chapter, we first study the myriad factors to be considered in making our data persistent; we then play with most of the freely available Perl persistence modules and hold them up against the checklist of factors, to clearly understand their strengths and weaknesses and what they provide and where they expect the developer to step in. In the next chapter, we will use some of these modules to create an object persistence framework to store an object transparently in files and databases.

Persistence Issues

Data ranges from simple comma-delimited records to complex self-referential structures. Users vary in level of paranoia and their ability (and need) ...