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>The major downside is that it is an inherently non-scalable behavior for a database engine well, that is true for the whole SQL, but certainly not true for so

• jandrewrogers 13y ago
  Actually, it is not true for the whole SQL. It is just true for implementations that require secondary indexing or extensive denormalization. This is essentially the way you would implement SQL if you were copying 1990s database kernel design but it is not the only way. Unfortunately, almost everyone still implements database engines this way because that is the way they have traditionally been designed; designing a genuinely new database kernel from scratch is not for the faint of heart. I normally design around databases in the tens of terabytes to tens of petabytes range, it is not an unusual scale. A database engine designed as the parent outlined would start to exhibit unacceptable performance characteristics at single-digit terabyte scales. A terabyte is tiny; I can buy servers with that much memory. Complex multi-attribute selection and joins are efficiently parallelizable but most databases do not implement algorithms and data structures that allow this to be realized.