How to transition from Equivalent Indexes to Index Replicas?

In the previous post, we saw the benefits of using index replicas over equivalent indexes.  Let’s say you are on Couchbase Server 4.x and have the following 3 equivalent indexes spread across 3 nodes; and with Couchbase 5.0 Beta available, you want to migrate these equivalent indexes to Index Replicas.

//old 4.x equivalent indexes
create index eq_index1 on bucket(field1); 

create index eq_index2 on bucket(field1); 

create index eq_index3 on bucket(field1);

Note: If you want to use the same nodes to create the replicas, do make sure that they have the required memory and compute resources for the both the index replicas and equivalent indexes to coexist.

Step 1: Fire the following query with the num_replica parameter being 2, as we earlier had 3 copies of the index and want to maintain the same topology of indexes.

create index eq_index on bucket(field1) with {“num_replica”:2}

If you are bringing in a new set of 3 index nodes, then you might as well specify the ‘create index’ statement with the ‘nodes’ parameter set; for example:

create index eq_index on bucket(field1) with {“nodes” [“10.10.10.1:9001", "10.10.10.2:9002", "10.10.10.3:9003”]}

Step 2: Once Step1 completes and all the index replicas are created and online(i.e, index build completed), drop the old 4.x equivalent indexes present.

drop index eq_index1; 
drop index eq_index2; 
drop index eq_index3;

Voila!! Your N1QL queries are all set to use the index replicas, and there was no application downtime during the process as well. If you had used ‘USE INDEX’ directive in your N1QL query, then the same needs to be updated with the new index name.

Equivalent indexes are still supported in Couchbase Server 5.0 and a mix of equivalent and replica indexes also works, i.e.,  N1QL queries would load balance between equivalent and replica indexes; but for efficient manageability, index replicas are recommended over equivalent indexes.

If you haven’t already, click here to download Couchbase Server 5.0 and play around with Index Replicas.