Immediate consistency

EventStoreDB
1

Hi guys, I’m new to event store and have a question regarding eventual consistency.

Is it correct, that if I append an event to a stream and right after read from the stream, that there is a guarantee (immediate consistency) that the event will be there?

  1. Appending to a stream in a single write

Task<WriteResult> AppendToStreamAsync(string stream, long expectedVersion, IEnumerable<EventData> events)

https://eventstore.org/docs/dotnet-api/writing-to-a-stream/index.html#appending-to-a-stream-in-a-single-write

  1. Read a specific stream backwards

Task<StreamEventsSlice> ReadStreamEventsBackwardAsync(string stream, long start, int count, bool resolveLinkTos)

https://eventstore.org/docs/dotnet-api/reading-events/index.html#read-a-specific-stream-backwards

I tested it and it seems to be the case but I don’t have the testing possibility at the moment to verify that it’s 100% the case also in production after collection much more streams and events then I currently have.

I couldn’t find the information in the docs, if there is, that would be very helpful :slight_smile:

2

In a cluster “it depends” it depends on whether you read from a single node or multiple (quorum). Writes will by default always be to a quorum so if you set expected version properly you will always get an error in the edge case.

3

Hi Greg,

In a cluster “it depends” it depends on whether you read from a single node or multiple (quorum).

I have a multi node cluster and connect with PerformOnMasterOnly (the default).

Is my understanding correct, that I get immediate consistency since all write and read requests are served only by the master?

I’m unsure since I read that the master will forward writes to all nodes and will consider it to be done when n/2+1 have agreed its been done.

thanks a lot for your help!

Koji

4

It will be known of on the master due to how it works always, it may not be be persisted in the master but it will be known about.