With limited data (say an year worth of notes?) TiddlyWiki is actually quite good.
It matches your requirements of being light while its not too large, you can zip the single HTML file and use it with your favorite browser.
Its problem starts when you want to host from remote machines (rather than your local machine) and when multiple people want to work with it -- that is when you should consider MediaWiki.
Normally, for single-user TiddlyWiki, you could just keep a
git archive on the central server and pull it out whenever you want to work with it (rather than hosting from a remote server).
To keep things light, consider a tag-set that will categorize entries which need to be available long-term (across months or years) and switch to a new TiddlyWiki HTML periodically (migrate the long-term entries to the new file -- TiddlyWiki supports that). This will keep the working HTML file small.
But there are other alternatives like Evernote too -- with a lot of other useful features.