Counter values become under-counted when running repair.

We are experimenting Counters in Cassandra 2.2.5. Our setup is that we have 6 nodes, across three different regions, and in each region, the replication factor is 2. Basically, each nodes holds a full copy of the data.

We are writing to cluster with CL = 2, and reading with CL = 1.

When are doing 30k/s counter increment/decrement per node, and at the meanwhile, we are double writing to our mysql tier, so that we can measure the accuracy of C* counter, compared to mysql.

The experiment result was great at the beginning, the counter value in C* and mysql are very close. The difference is less than 0.1%.

But when we start to run the repair on one node, the counter value in C* become much less than the value in mysql, the difference becomes larger than 1%.

My question is that is it a known problem that the counter value will become under-counted if repair is running? Should we avoid running repair for counter tables?

Thanks.