It's been almost two years I've been using HSQLDB in one of my client-critical application. When I was given the task of working on this application (which was already in production), main challenge was to reduce latency and also to make it flexible enough to accommodate any future use-cases. Without going into to much details, here's my use-case: Application receives data from multiple sources Parse data from each source and extract required data Aggregate this extracted data and find best candidate which satisfies certain rules One simplest solution is to join data from all sources by having a (for-)loop, one each for a source and apply rules inside inner-most loop. As number of data sources increases, so does the latency. HSQLDB came to my rescue. I used in-memory variant, as the data is non more required, once a candidate is found. Data extracted from each source is stored into DB (from here on, DB => in-memory HSQLDB), where