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30.1.1.JIT Accelerated Operations

30.1.2. Inlining

30.1.3. Optimization

CurrentlyPostgres Pro'sJIT implementation has support for accelerating expression evaluation and tuple deforming. Several other operations could be accelerated in the future.

Expression evaluation is used to evaluateWHERE clauses, target lists, aggregates and projections. It can be accelerated by generating code specific to each case.

Tuple deforming is the process of transforming an on-disk tuple (seeSection 66.6.1) into its in-memory representation. It can be accelerated by creating a function specific to the table layout and the number of columns to be extracted.

Postgres Pro is very extensible and allows new data types, functions, operators and other database objects to be defined; seeChapter 36. In fact the built-in objects are implemented using nearly the same mechanisms. This extensibility implies some overhead, for example due to function calls (seeSection 36.3). To reduce that overhead,JIT compilation can inline the bodies of small functions into the expressions using them. That allows a significant percentage of the overhead to be optimized away.

LLVM has support for optimizing generated code. Some of the optimizations are cheap enough to be performed wheneverJIT is used, while others are only beneficial for longer-running queries. Seehttps://llvm.org/docs/Passes.html#transform-passes for more details about optimizations.