With a big database (I’ve certainly got one ) DEVONthink is making heavy use of RAM and Virtual Memory. There’s a lot of processing going on when you do some types of searches, and certainly when you use the Classify and See Also features. VM scratch files build up, and data gets paged back and forth to RAM.
Your practice of using the Backup & Optimise tool regularly is a good one, and helps keep the database running well – as well as assuring a recent backup of your work.
Another trick that I use, when DT gets sluggish, is to close the database, then relaunch it.
Another trick – an important one – is to keep System and disk operations clean and healthy. Disk Utility can be used to repair Permissions, and this should be done before and after major software installations such as OS updates and security updates. There’s a ‘donation ware’ utility called AppleJack that allows disk repair, cache cleaning and so forth to be done from Safe mode – much faster and more convenient than starting up from a CD. There are several utilities, some freeware, that allow cron scripts to be run without going to the Terminal. DiskWarrior does a great job of catching and repairing disk errors and optimizing the directory. ‘Housekeeping’ helps ensure that your computer is running at its maximum performance, and protects your data.
I’m using a beta of DT Pro. Although DT PE and DT Pro were using the same basic ‘engines’ when DT PE 1.9.2 was released, the developers have continued to speed up DT Pro operations such as phrase searches. Phrase searches were recently tweaked to run an order of magnitude faster. Improvements like that will find their way into future versions of DT PE, as well. For example, you may be noticing a lag in response the first few times you do a search, or use the Classify button. DT Pro beta is now dramatically faster.
My own computer is a more than 4-year old TiBook 500 MHz, with 1 GB RAM. I continue to be awed by how fast DEVONthink performs on my database, which is much larger than the one you had tried.
Bottom line: DT (including PE) can run fast, even with databases much larger than mine. A bit of routine housekeeping can ensure continued quick operations.
Future news: DEVONtech will introduce a revamped database structure in upcoming versions. Transition to the new structure will be smooth. Memory usage will be reduced. Many DT operations will receive a 5 to 10-fold speed boost (on top of the boosts I noted above in DT Pro beta). Spotlight will be able to see your files under OS X 4. But DT will do so much more than Spotlight that you will want to put more and more things into DEVONthink.