I worked at a company that did a very large amount of data processing on a relatively small number of machines using a well-optimized c++ library. The library did everything, including the calculations and the data storage. This made it hard to write one-off queries that the executive team would request from time to time, since we would write a custom c++ program every time.
One day we came up with an idea: what if we could query the data store with SQL? The first iteration actually attempted to embed sqlite3 into the data access layer, which was functional but extremely slow because of all the type marshaling going on. A coworker and I came up with the second iteration which worked like this: a custom SQL-like language would be parsed by a Perl program using Parse::RecDescent, a recursive parser generator. The parse tree would then be translated into C++ that used the data access layers and processing layers directly. The compiled program was distributed to the cluster in the same way as the daily processes.
As far as I know this monstrosity still gets daily use, four years later.
One day we came up with an idea: what if we could query the data store with SQL? The first iteration actually attempted to embed sqlite3 into the data access layer, which was functional but extremely slow because of all the type marshaling going on. A coworker and I came up with the second iteration which worked like this: a custom SQL-like language would be parsed by a Perl program using Parse::RecDescent, a recursive parser generator. The parse tree would then be translated into C++ that used the data access layers and processing layers directly. The compiled program was distributed to the cluster in the same way as the daily processes.
As far as I know this monstrosity still gets daily use, four years later.