Elasticsearch data consistency


(famoss) #1

1.Es create a document says:

Node 3 executes the request on the primary shard. If it is successful, it forwards the request in parallel to the replica shards on Node 1 and Node 2. Once all of the replica shards report success, Node 3 reports success to the coordinating node, which reports success to the client.

But,next consistency says:

default quorum, or majority

If i have 2 replica shard,i think es just need one replica shard report success instead of all of the replica shards report success?

2.Retrieving a Document says:

For read requests, the coordinating node will choose a different shard copy on every request in order to balance the load; it round-robins through all shard copies.

So,if one replica shard index a doc error and another success,i will get different result from different shards?


(Luca Cavanna) #2

Hi,
consistency is not the best wording (which we will change in future versions). This is not about whether the operation is successful or not. A write operation cannot be rolled back anyways. It is a pre-write check to verify that we have enough available copies of the shard that we have to write into. With 2 replicas, we need to have available the primary and one replica for the write operation to come through. Otherwise the write will be rejected as a whole, it won't be executed in the primary either.

This should also answer you question on read operations.

Cheers
Luca


(famoss) #3

Thank you.


(system) #4

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