Re: File search

["Ludovic Courtès" <ludo@gnu.org>]

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> I also had the idea of making it a package... this way only the people
> who opt to install the database locally would incur the cost (in
> bandwidth).
>
> Perhaps a question for Vagrant: talking about size, is this SQLite
> database file comparable or smaller in size to the apt-file database
> that needs to be downloaded?  With the Debian software catalog being
> about 30% bigger, I'd expect a similarly bigger file size.
>
> If Debian is doing better in terms of database file size, we could look
> at how they're doing it.

As a back-of-the-envelope estimate, here’s the amount of text that needs
to be available in the database:

--8<---------------cut here---------------start------------->8---
ludo@berlin ~/src$ sqlite3 -csv  /tmp/db 'select name,version from packages; select name from directories;select name from files;'|wc -c
197689978
ludo@berlin ~/src$ guile -c '(pk (/ 197689978 (expt 2. 20)))'

;;; (188.5318546295166)
ludo@berlin ~/src$ du -h /tmp/db
389M    /tmp/db
--8<---------------cut here---------------end--------------->8---

So roughly, SQLite with this particular schema ends up taking twice as
much space as the lower bound.

We can do a bit better (I’m not an expert, so I’m just trying things
naively) by dropping the index and cleaning up the database:

--8<---------------cut here---------------start------------->8---
ludo@berlin ~/src$ cp /tmp/db{,.without-index}
ludo@berlin ~/src$ sqlite3  /tmp/db.without-index
SQLite version 3.32.3 2020-06-18 14:00:33
Enter ".help" for usage hints.
sqlite> drop index IndexFiles;
sqlite> .quit
ludo@berlin ~/src$ du -h /tmp/db.without-index 
389M    /tmp/db.without-index
ludo@berlin ~/src$ sqlite3  /tmp/db.without-index 
SQLite version 3.32.3 2020-06-18 14:00:33
Enter ".help" for usage hints.
sqlite> vacuum;
sqlite> .quit
ludo@berlin ~/src$ du -h /tmp/db.without-index 
290M    /tmp/db.without-index
--8<---------------cut here---------------end--------------->8---

With compression:

--8<---------------cut here---------------start------------->8---
ludo@berlin ~/src$ zstd -19 < /tmp/db.without-index > /tmp/db.without-index.zst
ludo@berlin ~/src$ du -h /tmp/db.without-index.zst 
37M     /tmp/db.without-index.zst
--8<---------------cut here---------------end--------------->8---

(Down from 61MB.)  For comparison, this is smaller than guile, perl,
gtk+, and roughly the same as glibc:out.

For the record, with compression, the lower bound is about 12 MiB:

--8<---------------cut here---------------start------------->8---
ludo@berlin ~/src$ sqlite3 -csv  /tmp/db 'select name,version from packages; select name from directories;select name from files;'|zstd -19|wc -c
12128674
ludo@berlin ~/src$ guile -c '(pk (/ 12128674 (expt 2. 20)))'

;;; (11.566804885864258)
--8<---------------cut here---------------end--------------->8---

All this to say that we could distribute the database in a form that
gets closer to the optimal size, at the expense of extra processing on
the client side upon reception to put it into shape (creating an index,
etc.).

Ludo’.