SQlite heavily depends on the underlying filesystem locking functionality so it should be used with caution, more details here When SQLite is searching for something it would first check this temporary file and if nothing is found proceed with the main database file.Īs a result, readers don’t compete with writers and performance is much better compared to the Old Way. In this case all writes are appended to a temporary file ( write-ahead log) and this file is periodically merged with the original database. If something crashes in the middle of writing into the database file it would pick up this temporary file and revert the changes from it Write-Ahead Logging or WAL (New Way) Prior to writing something to the database file SQLite would first save the chunk to be changed in a temporary file. This is why here they’re saying SQlite implements serializable transactions TroublesĪs it needs to lock an entire database every time and everybody waits for a process handling writing concurrency suffers and such concurrent writes/reads are of fairly low performance Rollbacks/outages (This is known as a multiple-readers-single-writer or MSRW lock) Multiple readers can co-exist and read something in parallel.ĭuring writing it makes sure an exclusive lock is acquired and no other process is reading/writing simultaneously and hence writes are safe. That means whenever it needs to read/write something it first acquires a lock on the ENTIRE database file. In this mode SQLite uses DATABASE-LEVEL locking. Such ACID support as well as concurrent read/writes are provided in 2 ways - using the so-called journaling (lets call it “ old way”) or write-ahead logging (lets call it “ new way”) Journaling (Old Way) Lets figure out why SQLite is transactionalĪll changes within a single transaction in SQLite either occur RAM is several orders of magnitude faster than disk. If you want really fast read/write access, use an in-memory SQLite database. In fact, with modern disks and processors, 95% of web sites and web services would work just fine with SQLite. blogs, forums), and I have yet to see any evidence to the contrary. (Firefox uses SQLite extensively for bookmarks, history, etc.)įor server applications, somebody some time ago said that anything less than 100K page views a day could be handled perfectly by a SQLite database in typical scenarios (e.g. Especially SQLite 3.įor most desktop/laptop/tablet/phone applications, SQLite is fast enough as there's not enough concurrency. A lot would then depend on how fast your filesystem is, since the SQLite engine itself is extremely fast and has many clever optimizations to minimize contention. But if you start writing concurrently, lock contention could become an issue. SELECT), SQLite can handle them very well. If most of those concurrent accesses are reads (e.g.
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