"Our first goal was testing of existed current release versions of
InterBase and Firebird – InterBase 7.5.1 and Firebird 1.5.2
accordingly. Well, we've encountered problems with InterBase 7.5.1
testing – it generated so bad plan for queries 3 and 20 that we were
not able to wait its finishing, so these queries were omitted in test
results."

http://ibdeveloper.com/tests/tpc-r/interbase-751-and-firebird-152-tpc-r-based-test-results/
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developer flamerobin.org