Change Details

We want to evaluate the practical performance implications of using a single, local, cache backend instead of spreading the whole datastet to multiple nodes with c-hashing. In order to do so, we need to change the current Puppetization to allow taking one host out of c-hash, and use it exclusively as a local backend. This could be done by using a hiera setting, say `cache::single_backend_fqdn`, and excluding such hostname from the pool of backends for a given cache cluster/DC. Additionally, we need to use only localhost as the cache backend for the host `cache::single_backend_fqdn` itself.

We want to evaluate the practical performance implications of using a single, local, cache backend instead of spreading the whole datastet to multiple nodes with c-hashing. In order to do so, we need to change the current Puppetization to allow taking one host out of c-hash, and use it exclusively as a local backend. This could be done by using a hiera setting, say `cache::single_backend_fqdn`, and excluding such hostname from the pool of backends for a given cache cluster/DC. Additionally, we need to use only localhost as the cache backend for the host `cache::single_backend_fqdn` itself. Dashboards such as [[ https://grafana.wikimedia.org/d/A__2L7eWz/cache-hosts-comparison?orgId=1 | cache-hosts-comparison ]] can then be used to observe the impact on hitrate/ttfb on various nodes. By having N-1 backend nodes instead of N there may be some backend hitrate change across the board to take into account when interpreting the results.

We want to evaluate the practical performance implications of using a single, local, cache backend instead of spreading the whole datastet to multiple nodes with c-hashing. In order to do so, we need to change the current Puppetization to allow taking one host out of c-hash, and use it exclusively as a local backend. This could be done by using a hiera setting, say `cache::single_backend_fqdn`, and excluding such hostname from the pool of backends for a given cache cluster/DC. Additionally, we need to use only localhost as the cache backend for the host `cache::single_backend_fqdn` itself. Dashboards such as [[ https://grafana.wikimedia.org/d/A__2L7eWz/cache-hosts-comparison?orgId=1 | cache-hosts-comparison ]] can then be used to observe the impact on hitrate/ttfb on various nodes. By having N-1 backend nodes instead of N there may be some backend hitrate change across the board to take into account when interpreting the results.