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Code of Conduct

This project and everyone participating in it is governed by a Code of Conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to

Did you find a bug?

  • Ensure the bug was not already reported by searching on GitHub under Issues.
  • If you're unable to find an open issue addressing the problem, open a new one. Be sure to include a title and clear description, as much relevant information as possible, and a code sample or an executable test case demonstrating the expected behavior that is not occurring.

Did you write a patch that fixes a bug?

  • Great!
  • If possible, add a unit test case to make sure the issue does not occur again.
  • Make sure you run the code formatter (make format).
  • Open a new GitHub pull request with the patch.
  • Ensure the PR description clearly describes the problem and solution. Include the relevant issue number if applicable.


  • Do not commit/push directly to the master branch. Instead, create a feature branch/fork and file a merge request.
  • When maintaining a branch, merge frequently with the master.
  • When maintaining a branch, submit merge requests to the master frequently.
  • If you are working on a bigger issue try to split it up into several smaller issues.


  • make unit runs the fast unit tests (~one minute), make allunit runs all unit tests (~one hour).
  • Make sure all unit tests pass before merging into the master branch.
  • Write many tests
  • Test with different types, especially numerics and strings
  • Try to test unexpected/incorrect usage as well, instead of only the happy path
  • Slower tests should be added to the all unit tests. You can do this by adding [.] after the test group. For an example see test_tpch.cpp.
  • Look at the code coverage report of your branch and attempt to cover all code paths in the fast unit tests. Attempt to trigger exceptions as well. It is acceptable to have some exceptions not triggered (e.g. out of memory exceptions or type switch exceptions), but large branches of code should always be either covered or removed.


  • Tabs for indentation, spaces for alignment
  • 120 columns
  • clang_format enforces these rules automatically, use make format to run the formatter.

C++ Guidelines

  • Do not use malloc, prefer the use of smart pointers
  • Strongly prefer the use of unique_ptr over shared_ptr, only use shared_ptr if you absolutely have to
  • Do not import namespaces in headers (e.g. using std), only in source files
  • When overriding a virtual method, avoid repeating virtual and always use override or final
  • Use [u]int(8|16|32|64)_t instead of int, long, uint etc. In particular, use index_t instead of size_t for offsets/indices/counts of any kind.
  • Prefer using references over pointers
  • Use C++11 for loops when possible: for (const auto& item : items) {...}
  • Use braces for indenting if statements and loops. Avoid single-line if statements and loops, especially nested ones.
  • Class Layout: Start out with a public block containing the constructor and public variables, followed by a public block containing public methods of the class. After that follow any private functions and private variables.

Error Handling

  • Use exceptions only when an error is encountered that terminates a query (e.g. parser error, table not found). Exceptions should only be used for exceptional situations. For regular errors that does not break the execution flow (e.g. errors you expect might occur) use a return value instead.
  • Try to add test cases that trigger exceptions. If an exception cannot be easily triggered using a test case then it should probably be an assertion. This is not always true (e.g. out of memory errors are exceptions).
  • Use assert only when failing the assert means a programmer error. Assert should never be triggered by a user input. Avoid code like assert(a > b + 3); without comments or context.
  • Assert liberally, but make it clear with comments next to the assert what went wrong when the assert is triggered.

Naming Conventions

  • Files: lowercase separated by underscores, e.g., abstract_operator.cpp
  • Types (classes, structs, enums, typedefs, using): CamelCase starting with uppercase letter, e.g., BaseColumn
  • Variables: lowercase separated by underscores, e.g., chunk_size
  • Functions: CamelCase starting with uppercase letter, e.g., GetChunk
  • Choose descriptive names.
  • Avoid i, j, etc. in nested loops. Prefer to use e.g. column_idx, check_idx. In a non-nested loop it is permissible to use i as iterator index.
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