This is the issue noted in #76. Keeping all historical results of
queries in the HistoricalQueryResults struct makes serializing and
deserializing those structs very, very slow as time goes on. By only
storing the last execution of the query, we keep the performance
constant, but we kill the feature where osquery can rebuild timelines
without accessing logs. After talking it over, we decided that this
isn't actually that big of a deal because, if you really wanted to
rebuild the old data, you should be able to process the logs, similarly
to bin log replication in MySQL.
