Concurrency and networking

Concurrency and networking

High level picture: ACID?

Similar to some other popular NoSQL solutions, tiedot does not provide ACID transactions. However:

• Atomic operations are possible within the scope of a single document.
• Durable writes are currently not possible with tiedot, but this feature is planned in the next release.

IO operation synchronization

For maximum performance and scalability, tiedot only synchronizes IO operations at very low level - each data file (documents or index) has a RWMutex (read-write lock).

There are only 4 operations which incur read lock:

• Read document ( without JSON parsing)
• Scan collection ( without JSON parsing)
• Scan hash table (all entries)
• Scan hash table (by hash key)

And only 5 operations incur write lock:

• Insert/update/delete document ( without JSON parsing)
• Put/remove hash entry

Nothing else locks!

HTTP endpoint synchronization

Most of HTTP endpoints never lock, however there is a small number of operations which must "stop the world" to ensure safe operation - these operations block all other HTTP endpoints until completed:

• Create/rename/drop/scrub collection
• Create/remove index

The synchronization behaviour is controlled by a RWMutex - "stop the world" operations put write lock on it, all other operations put read lock on it.

HTTP service

tiedot HTTP service is powered by HTTP server in standard Golang library net/http.

The HTTP service:

• Listens on all network interfaces
• Listens on the port specified by user via CLI parameter
• Unconditionally processes all incoming requests
• Scalability is affected by GOMAXPROCS

See "HTTP API Reference" for documentation HTTP service usage.

Once tiedot enters HTTP service mode, it keeps running in foreground until:

• /shutdown endpoint is called (gracefully shutdown)
• Process is stopped/interrupted/killed (not good!)