title: Fastest and stable non-sql database?
body: <p>What is the fastest and most stable non-sql database to store big data and process thousands requests during the day (it's for traffic exchange service)? I've found Kdb+ and Berkeley DB. Are they good? Are there other options?</p>
  
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  <p>Each day server processes > 100K visits. For each visit I need to read corresponding stats from DB, write log to DB and update stats in DB, aka 3 operations with DB per visit. Traffic is continuously increasing. Thus DB engine should be fast. From one side DB will be managed by demon written on C, Erlang or any other low-level language. From another side DB will be managed by PHP scripts. </p>