1. A computer-implemented method for caching values during an extract transform load (ETL) process in a manufacturing execution system (MES), the method comprising: preloading a cache with a subset of a set of key-value pairs stored in source data, with a goal of achieving at least a predetermined cache hit ratio for any request of a particular key-value pair among the set stored in the source data; receiving a request of a key-value pair; determining whether the requested key-value pair is in the preloaded cache; if the requested key-value pair is in the preloaded cache, retrieving the requested key-value pair from the preloaded cache; if the requested key-value pair is not in the preloaded cache, queuing the requested key-value pair in an internal data structure until a threshold number of accumulated requested key-value pairs are queued in the internal data structure; and executing, in response to the internal data structure queue meeting the threshold number of accumulated requested key-value pairs, a query of the source data for all of the accumulated requested key-value pairs, and a command to retrieve all of the accumulated requested key-value pairs from the source data.