I have set the prefetch value to 255
I don't believe this helps in this instance - it only helps when scrolling through the table - it'll grab 255 records at once. Usual values are ~50,000 so it grabs 50,000 records in a go.
Without being rude, why are you using the data browser tab for such a large number of records? At 100 GB, this is going to be a lot of rows ... why would you want these all displayed? Usually, once the data is in the database, you perform actions on that data - how many records with a value of X in field Y, how many records with a value of Y in field Z, etc. You can perform that using SQL - eg, you don't view all million rows to find out there are a million rows. If you're scrolling through data, you can use 'limit' to make this manageable.
In my eyes, this is like opening a 900,000 page word document, then wondering why it takes a while to scroll up and down. Some will argue that DB4S should handle 80 million rows, but I fail to see the advantage of viewing this on screen... (just my personal opinion, of course!)
I don't want to re-open the issue and bother the developers if I made a mistake...
I would recommend opening a new issue, and making reference to the other issue - don't open an older one. The older one refered to a different version of DB4S, plus it will notify the original poster, when really you need your own new shiny issue that belongs just to you. Open it up as it might highlight something wrong with DB4S that can be fixed.
There is already an open issue where the number of rows visible in the grid is limited - possible due to the control we use in DB4S. This comes back to my (waaaaaaaay too long) point above that displaying a large number of results is a nuts thing to do anyway.
But if DB Browser for SQLite is really built in a way to forcibly load the entire database
Not intentionally it doesn't - there is a lot of work to make it as smooth as possible (the reason for the 'prefetch block size') but the first thing it has to do is work out how many rows the table has, so it does a 'select count(*) from table', and it's this that can hammer large databases. Even with an index, a 100 GB database is going to take time to get this figure.
How do you manage to count the number of rows so quickly ?
I knoweth not. I tend to steer clear of the DB4S code ... here be dragons. I know a lot has gone into making it optimised though... tweaks here and there, etc.
The application log in DB4S might assist in working out where the freeze is occurring.
If you don't need to edit records, the 'execute SQL' tab is useful to grab records, and that should be speedy. The grid is 'read only' which isn't always great.
But I thought it was impossible to have an accurate count of the number of rows quickly (i.e. faster than "select count(*)" which is taking ages
Depends on the version of SQLite. I know SQLite itself (so not DB4S) has sexy internal methods to make this query fast. Depending on the table contents, it can be quicker doing a 'select (1)' rather than a 'select (*)' which would pull in a load of data, only to discard it.
So there is something wrong around this last query but no means for me to debug this further
That's useful to know - thanks for digging that out.
I would have suggested raising an official issue for it, as it's something we'd like to get fixed, but development has ... er, kinda stalled at the moment and the issue count is >470, so it's going to get lost in the noise for a while, so won't get solved in the short-term.
I have a sqlite database with many tables, is there any way to set certain tables to be read-only?
Unfortunately not - a database is a collection of tables, and each table is a collection of rows. That data is either all readable, or if the database is in a read-only file structure, all the data is read-only. If you wanted certain tables to be read-only, you'd have to separate them out into their own database, and make that database read-only. You could then attach the two databases together. This isn't a great solution though, and if someone moved the database to a non-read-only location, could manipulate the database again.
You could encrypt the database, but again, that's an all-or-nothing - you can't just encrypt individual tables. Unless, you wrote the data yourself, of course - if your own application read/wrote to the database, you could write data in an encrypted format so 'joe public' couldn't edit it.
where can I set the command for "Open in external application"?
I believe this saves a .txt file and tries to open that using whatever application normally opens a .txt file. In Firefox, what file is it showing? I assume you're editing text, and not an image or binary data. What operating system are you using?