We have solr router and shards. This appears in the jetty log of the router when doing faceted search across all the shards.
org.apache.commons.httpclient.HttpMethodDirector executeWithRetry
INFO: I/O exception (java.net.SocketException) caught when processing request: Connection reset by peer: socket write error
org.apache.commons.httpclient.HttpMethodDirector executeWithRetry
INFO: Retrying request
followed by exception about Internal Server Error. We run eighty shards distributed across several servers. Router runs on its own node.
UPD: In the HttpCommComponent class of SOLR which sumbits requests to shards using HttpClient class I have noticed the following set on the MultiThreadedHttpConnectionManager: mgr.getParams().setDefaultMaxConnectionsPerHost(20);
it seems to me like too little setting for 80+ shards.