It Depends (tm). There are several issues when communications are unreliable, basically all having to do with timeouts.
> ZK not getting "keep alive" requests back in time and marking the node as down > leaders not getting responses back in time from followers in time and putting > them into recovery. > client timeouts because of slow connections Plus, consider a single Solr query in a sharded environment. It has to: > send a sub request to one replica of each shard > get the sub request back > sort the true top N > request the actual doc from each replica in the first step > send the final response to the client. Or indexing. Let's say you get a doc in to replica N. Then > the doc is forwarded to the leader for the appropriate shard > the doc is sent to each replica in that shard > the response comes back to the leader > the response is ack'd back to the original node receiving the request > the response is ack'd back to the client. The point is that there's a _lot_ of communication between Solr nodes, and if you have a slow pipe connecting them overall latency is increased. But whether that latency is acceptable for your application only you can tell. But be a little careful here. None of the above addresses a "problematic network" in the sense that a slow network is totally expected. CDCR is intended to solve the problem of "problematic" being defined as separate data centers connected by a network with latency. Best, Erick On Mon, Jul 23, 2018 at 3:01 AM, Pavel Micka <pavel.mi...@zoomint.com> wrote: > Hi, > > We are discussing advantages of SolrCloud Replication and Cross Data Center > Replication (CDCR). In CDCR docs, it is written that > "The SolrCloud architecture is not particularly well suited for situations > where a single SolrCloud cluster consists of nodes in separated data clusters > connected by an expensive pipe". > > But we fail to find, what latency is acceptable for SolrCloud/ZK and when we > should start considering using CDCR (master-slave). And what would be the > issues if we install SolrCloud on problematic network? > > Thanks in advance, > > Pavel
