to improve sqlite performance

INSERT is really slow - I can only do few dozen INSERTs per second

http://www.sqlite.org/faq.html#q19

Actually, SQLite will easily do 50,000 or more INSERT statements per second on an average desktop computer. But it will only do a few dozen transactions per second. Transaction speed is limited by the rotational speed of your disk drive. A transaction normally requires two complete rotations of the disk platter, which on a 7200RPM disk drive limits you to about 60 transactions per second.

Transaction speed is limited by disk drive speed because (by default) SQLite actually waits until the data really is safely stored on the disk surface before the transaction is complete. That way, if you suddenly lose power or if your OS crashes, your data is still safe. For details, read about atomic commit in SQLite..

By default, each INSERT statement is its own transaction. But if you surround multiple INSERT statements with BEGIN...COMMIT then all the inserts are grouped into a single transaction. The time needed to commit the transaction is amortized over all the enclosed insert statements and so the time per insert statement is greatly reduced.

Another option is to run PRAGMA synchronous=OFF. This command will cause SQLite to not wait on data to reach the disk surface, which will make write operations appear to be much faster. But if you lose power in the middle of a transaction, your database file might go corrupt.

http://blogs.msdn.com/b/andy_wigley/archive/2013/11/21/how-to-massively-improve-sqlite-performance-using-sqlwinrt.aspx

http://blog.quibb.org/2010/08/fast-bulk-inserts-into-sqlite/

http://www.codeproject.com/Articles/853842/Csharp-Avoiding-Performance-Issues-with-Inserts-in

http://stackoverflow.com/questions/1711631/improve-insert-per-second-performance-of-sqlite

threadsafe / sqlite in multithread

https://www.sqlite.org/threadsafe.html

I read everywhere that creating transactions is the solution to slow SQLite writes, but it can be long and painful to rewrite your code and wrap all your SQLite writes in transactions.

I found a much simpler, safe and very efficient method: I enable a (disabled by default) SQLite 3.7.0 optimisation : the Write-Ahead-Log (WAL). The documentation says it works in all unix (i.e. Linux and OSX) and Windows systems.

How ? Just run the following commands after initializing your SQLite connection:

PRAGMA journal_mode = WAL
PRAGMA synchronous = NORMAL

My code now runs ~600% faster : my test suite now runs in 38 seconds instead of 4 minutes :)