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MAL reference

The primary textual interface to the Monetdb kernel is a simple, assembly-like language, called MAL. The language reflects the virtual machine architecture around the kernel libraries and has been designed for speed of parsing, ease of analysis, and ease of target compilation by query compilers. The language is not meant as a primary programming language, or scripting language. Such use is even discouraged.

Furthermore, a MAL program is considered a specification of intended computation and data flow behavior. It should be understood that its actual evaluation depends on the execution paradigm choosen in a scenario. The program blocks can both be interpreted as ordered sequences of assembler instructions, or as a representation of a data-flow graph that should be resolved in a dataflow driven manner. The language syntax uses a functional style definition of actions and mark those that affect the flow explicitly. Flow of control keywords identify a point to chance the interpretation paradigm and denote a synchronization point.

MAL is the target language for query compilers front-ends. Even simple SQL queries generate a long sequence of MAL instructions. They represent both the administrative actions to ensure binding and transaction control, the flow dependencies to produce the query result, and the steps needed to prepare the result set for delivery to the front-end.

Only when the algebraic structure is too limited (e.g. updates), or the database back-end lacks feasible builtin bulk operators, one has to rely on more detailed flow of control primitives. But even in that case, the basic blocks to be processed by a MAL back-end are considered large, e.g. tens of simple bulk assignment instructions.

The remainder of this chapter provide a concise overview of the language features and illustrative examples