Question

I’m programming a simple customer-information management software now with SQLite.

One exe file, one db file, some dll files. – That’s it 🙂

2~4 people may be going to run this exe file simultaneously and access to a database.

Not only just reading but frequent editing will be done by them too.

Yeahhh now here comes the one of the most famous problems… “Synchronization”

I was trying to create / remove a temporary empty file whenever someone is trying
to edit it. (this is a ‘key’ to access the db.)

But there must be a better way for it : (

What would be the best way of preventing this problem?

Answer 1

Well, SQLite already locks the database file for each use, the idea being that multiple applications can share the same database.

However, the documentation for SQLite explicitly warns about using this over the network:

SQLite will work over a network
filesystem, but because of the latency
associated with most network
filesystems, performance will not be
great. Also, the file locking logic of
many network filesystems
implementation contains bugs (on both
Unix and Windows). If file locking
does not work like it should, it might
be possible for two or more client
programs to modify the same part of
the same database at the same time,
resulting in database corruption.
Because this problem results from bugs
in the underlying filesystem
implementation, there is nothing
SQLite can do to prevent it.

A good rule of thumb is that you
should avoid using SQLite in
situations where the same database
will be accessed simultaneously from
many computers over a network
filesystem.

So assuming your “2-4 people” are on different computers, using a network file share, I’d recommend that you don’t use SQLite. Use a traditional client/server RDBMS instead, which is designed for multiple concurrent connections from multiple hosts.

Your app will still need to consider concurrency issues (unless it speculatively acquires locks on whatever the user is currently looking at, which is generally a nasty idea) but at least you won’t have to deal with network file system locking issues as well.