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reactive semantics

Tyler Neely edited this page Jul 9, 2019 · 4 revisions

As of sled 0.16.8 we support the watch_prefix feature which allows a caller to create an iterator over all events that happen to keys that begin with a specified prefix. Supplying an empty vector allows you to subscribe to all updates on the Tree.

reactive architectures

Subscription to keys prefixed with "topic names" can allow you to treat sled as a durable message bus.

replicated systems

Watching the empty prefix will subscribe to all updates on the entire database. You can feed this into a replication system

analysis tools and auditing

ordering guarantees

Updates are received in-order for particular keys, but updates for different keys may be observed in different orders by different Subscribers. As an example, consider updating the keys k1 and k2 twice, adding 1 to the current value. Different Subscribers may observe the following histories:

Set(k1, 100), Set(k1, 101), Set(k2, 200), Set(k2, 201)
or
Set(k1, 100), Set(k2, 200), Set(k1, 101), Set(k2, 201)
or
Set(k1, 100), Set(k2, 200), Set(k2, 201), Set(k1, 101)
or
Set(k2, 200), Set(k1, 100), Set(k1, 101), Set(k2, 201)
or
Set(k2, 200), Set(k1, 100), Set(k2, 201), Set(k1, 101)
or
Set(k2, 200), Set(k2, 201), Set(k1, 100), Set(k1, 101)
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