On Wed, Nov 03, 2010 at 05:10:22PM +0300, Alexey Pechnikov scratched on the wall: > 2010/11/3 Jay A. Kreibich <j...@kreibi.ch> > > > > Why not just use an off-the-self hash cache, like memcached, or an > > off-the-self hash database, like Redis? Redis even supports an > > Append-Only write mode (e.g. WAL-ish journal mode). > > How about power fail or OS crash? As I know, Redis does not garantees the > data safety.
This is getting a bit off topic, but quickly... No, by default Redis does not provide the level of protection a default file-backed SQLite database provides. Redis's append-only mode does a pretty good job, however. Redis will update journal with each command, and a sync is performed every second. In theory, in the case of a power or OS crash, maximum data loss is right around one second worth of transactions. Application crash will not result in data loss, since the OS still has valid file buffers that will eventually be flushed. You can also configure things so that the journal syncs after each command, providing similar protection to SQLite. That is, as you might expect, somewhat slow, however. > And I think SQLite in-memory database is faster. Without testing, I'd guess Redis is faster for basic read/write operations. Redis is also a proper server and allows multiple client connections, even for a fully memory based data set. By default Redis will hold all data in RAM, and is highly optimized for one-- and only one-- basic operation, while SQLite is supporting a much richer and more expressive data processing environment. Each tool has its place, and they're not really trying to solve the same problem. The whole reason I'm looking to merge the two has to do with SQLite's expressive environment. In designing a very high-performance app, the highly-optimized common-case queries can talk to Redis directly. This is fast, but requires jumping through a lot of hoops in the application code. Conversely, the less frequent queries (including many of the management tasks) can talk to SQLite, which can then talk to Redis. Use of the SQL language makes development MUCH faster for those operations that are not as performance-critical. -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
