Re: Relational Model and Search Engines?

Leandro Guimarães Faria Corsetti Dutra <leandro_at_dutra.fastmail.fm> writes:
> Main memory is just a hype word for big cache, little
> reliability. It is just an implementation trick that's orthogonal to
> the database model.

I've seen some numbers for main memory databases being up 10-100 times faster than fully cached RDBMS. the issue is that these main memory databases have gone (back) to direct pointers ... but instead of being physical disk pointers ... there are direct memory addresses; ... while the RDBMS ... even with the database completely cached in memory ... is still threading thru indexes.

there was possibly an intermediate step in the 90s when some object database played games with direct pointers that were swizzled into direct memory pointers when things were resident in memory.

the issue for reliability more has to do with the transaction and commit boundaries and how they handle updates (being main memory doesn't preclude various journalling of changes to disk). somewhat to paraphrase, reliability/integrity can be an implementation trick that is orthogonal to the database model. the main memory can be initialized at start up from a combination of files on disk (say large scale striped array) and a journal. The issue of journal recovery time then is a performance issue ... but if you can perform updates 100 times faster, then possibly you can recover a journal a 100 times faster.

-- 
Anne & Lynn Wheeler | http://www.garlic.com/~lynn/