1. Create universe

If you have a previously running local universe, destroy it using the following.

$ ./yb-docker-ctl destroy

Start a new local universe with replication factor (RF) of 5. This will create five nodes.

$ ./yb-docker-ctl create --rf 5

Add two more nodes.

$ ./yb-docker-ctl add_node

$ ./yb-docker-ctl add_node

2. Write some data

By default, the YugabyteDB workload generator runs with strong read consistency where all data is read from the tablet leader. We are going to populate exactly one key with a 10 KB value into the system. Since the replication factor is 5, this key will get replicated to five of the seven nodes in the universe.

Run the CassandraKeyValue workload application to constantly update this key-value, as well as perform reads with strong consistency against the local universe.

$ docker cp yb-master-n1:/home/yugabyte/java/yb-sample-apps.jar .

$ java -jar ./yb-sample-apps.jar --workload CassandraKeyValue \
                                    --nodes localhost:9042 \
                                    --nouuid \
                                    --num_unique_keys 1 \
                                    --num_threads_write 1 \
                                    --num_threads_read 1 \
                                    --value_size 10240

In the above command, we have set the value of num_unique_keys to 1, which means we are overwriting a single key key:0. We can verify this using ycqlsh:

$ docker exec -it yb-tserver-n1 /home/yugabyte/bin/ycqlsh

Connected to local cluster at localhost:9042.
[ycqlsh 5.0.1 | Cassandra 3.9-SNAPSHOT | CQL spec 3.4.2 | Native protocol v4]
Use HELP for help.

ycqlsh> SELECT k FROM ybdemo_keyspace.cassandrakeyvalue;

 k
-------
 key:0

(1 rows)

3. Strongly consistent reads from tablet leaders

When performing strongly consistent reads as a part of the above command, all reads will be served by the tablet leader of the tablet that contains the key key:0. If we browse to the tablet-servers page, we will see that all the requests are indeed being served by one YB-TServer:

4. Timeline consistent reads from tablet replicas

Stop the running CassandraKeyValue workload application, and then run the following variant of that application. This command will do updates to the same key key:0 which will go through the tablet leader, but it will reads from the replicas.

$ java -jar ./yb-sample-apps.jar --workload CassandraKeyValue \
                                    --nodes localhost:9042 \
                                    --nouuid \
                                    --num_unique_keys 1 \
                                    --num_threads_write 1 \
                                    --num_threads_read 1 \
                                    --value_size 10240 \
                                    --local_reads

This can be easily seen by refreshing the tablet-servers page, where we will see that the writes are served by a single YB-TServer that is the leader of the tablet for the key key:0 while multiple Yb-TServers which are replicas serve the reads.

5. Clean up (optional)

Optionally, you can shut down the local cluster created in Step 1.

$ ./yb-docker-ctl destroy