![]() UDOs are written in C++ and compiled with Clang at optimization level -O3 to ELF object files, saving the intermediate LLVM bitcode in the process. To support custom algorithms that process the entire input at once (i.e., aggregations or sorting), the "Accept" function should store all tuples of the input, and the "Process" function should then iteratively loop over these tuples to compute the output. The "Process" function is invoked only once when all of the input tuples have been seen and is responsible for producing the output of the UDO by calling the "Emit" function, which sends one output tuple to the parent operator. The "Accept" function is invoked for each input tuple to the UDO and is responsible for implementing "per-tuple" processing. UDOs can be written in C++, conforming to an interface consisting of two functions: ![]() In addition to SQL and ArrayQL, Umbra allows the user to extend the functionality of the DBMS with custom algorithms with User-Defined Operators (UDOs). Umbra first generates x86 machine code using the Flying Start backend and then switches to the code generated by the LLVM backend for long-running queries. Umbra supports adaptive execution, pioneered by HyPer, allowing the DBMS to switch execution strategies while processing a single query. Additionally, Flying Start outperforms interpretation of Umbra IR, making Flying Start suitable for short-running queries. As a result, the code generated by Flying Start has performance on par with code generated by LLVM -O0 (i.e., with optimizations disabled). In addition, the Flying Start backend implements Stack Space Reuse, Machine Register Allocation, Lazy Address Calculation, and Comparison-Branch Fusion optimizations. The Flying Start backend emits x86 machine code using asmJIT, generating x86 in a single pass. This backend is the slowest but generates the fastest executing code, making it suitable for long-running queries. The LLVM backend emits LLVM IR, compiled at optimization level -O3. After generating Umbra IR, the code is lowered using one of two backends: Umbra performs Just-In-Time (JIT) compilation of queries into Umbra IR, a custom intermediate representation (IR) similar to LLVM IR but optimized for use in a database system.
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