""Andy Ballingall"" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED]
> On another thread, (not in this mailing list), someone mentioned that there > are a class of databases which, rather than caching bits of database file > (be it in the OS buffer cache or the postmaster workspace), construct a a > well indexed memory representation of the entire data in the postmaster > workspace (or its equivalent), and this, remaining persistent, allows the DB > to service backend queries far quicker than if the postmaster was working > with the assumption that most of the data was on disk (even if, in practice, > large amounts or perhaps even all of it resides in OS cache). As a historical note, System R (grandaddy of all relational dbs) worked this way. And it worked under ridiculous memory constraints by modern standards. Space-conscious MOLAP databases do this, FWIW. Sybase 11 bitmap indexes pretty much amount to this, too. I've built a SQL engine that used bitmap indexes within B-Tree indexes, making it practical to index every field of every table (the purpose of the engine). You can also build special-purpose in-memory representations to test for existence (of a key), when you expect a lot of failures. Google "superimposed coding" e.g. http://www.dbcsoftware.com/dbcnews/NOV94.TXT ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
