I've got an index with quite complex queries running on it. The main slowdown are the fuzzy queries which are run against a field containing 2-5 words for each record. I mainly have to find rows with 1-3 differing characters.
On my 4 core (with HT) and 8GB ram machine the my queries are executed in about 1-2s each. On a server with 12 cores (with HT) and 72Gb RAM the query executes in 0.3-0.5 seconds. This doesn't seem to me as a reasonable scaling on the hardware provided. I'm sure there should be some hidden options for me to tune to adjust the query performance.
I've looked through the elastic search guide but couldn't find there anything which would help me in tuning the performance based on the number of CPUs or RAM or tuning elastic specifically for fuzzy queries.
another question is how does it scale if i add another server like this? will the query time be roughly twice smaller?
There is a couple of possibilities here. First is that your query is I/O bound. In this case, just adding another server might help because two nodes will be retrieving data from two disks. Another possibility is that your query is CPU bound. To a large degree, search against a single shard is a single-threaded process. Assuming that your index was created with default settings, it has 5 shards. So, your query cannot significantly benefit from running on more than 5 CPUs. In this case, adding another node would only slow things down because of network overhead. Instead, you need to recreate index with more shards.