I am a user of Solr 3.2 and I make use of the distributed search capabilities of Solr using a fairly simple architecture of a coordinator + some shards.
Correct me if I am wrong: In a standard distributed search with QueryComponent, the first query sent to the shards asks for fl=myUniqueKey or fl=myUniqueKey,score. When the response is being generated to send back to the coordinator, SolrIndexSearcher.doc (int i, Set<String> fields) is called for each document. As I understand it, this will read each document from the index _on disk_ and retrieve the myUniqueKey field value for each document. My idea is to have a FieldCache for the myUniqueKey field in SolrIndexSearcher (or somewhere else?) that would be used in cases where the only field that needs to be retrieved is myUniqueKey. Is this something that would improve performance? In our actual setup, we are using an extended version of QueryComponent that queries for a couple other fields besides myUniqueKey in the initial query to the shards, and it asks a lot of rows when doing so, many more than what the user ends up getting back when they see the results. (The reasons for this are complicated and aren't related much to this question.) We already maintain FieldCaches for the fields that we are asking for, but for other purposes. Would it make sense to utilize these FieldCaches in SolrIndexSearcher? Is this something that anyone else has done before? -Michael
