facebook/kuduraft

A Raft Library in C++ based on the Raft implementation in Apache Kudu

Kudu Developer Documentation

Building and installing Kudu

Follow the steps in the documentation to build and install Kudu from source

Building Kudu out of tree

A single Kudu source tree may be used for multiple builds, each with its own build directory. Build directories may be placed anywhere in the filesystem with the exception of the root directory of the source tree. The Kudu build is invoked with a working directory of the build directory itself, so you must ensure it exists (i.e. create it with mkdir -p). It’s recommended to place all build directories within the build subdirectory; build/latest will be symlinked to most recently created one.

The rest of this document assumes the build directory <root directory of kudu source tree>/build/debug.

Automatic rebuilding of dependencies

The script thirdparty/build-if-necessary.sh is invoked by cmake, so new thirdparty dependencies added by other developers will be downloaded and built automatically in subsequent builds if necessary.

To disable the automatic invocation of build-if-necessary.sh, set the NO_REBUILD_THIRDPARTY environment variable:

$ cd build/debug
$ NO_REBUILD_THIRDPARTY=1 cmake ../..

This can be particularly useful when trying to run tools like git bisect between two commits which may have different dependencies.

Building Kudu itself

# Add <root of kudu tree>/thirdparty/installed/common/bin to your $PATH
# before other parts of $PATH that may contain cmake, such as /usr/bin
# For example: "export PATH=$HOME/git/kudu/thirdparty/installed/common/bin:$PATH"
# if using bash.
$ mkdir -p build/debug
$ cd build/debug
$ cmake ../..
$ make -j8  # or whatever level of parallelism your machine can handle

The build artifacts, including the test binaries, will be stored in build/debug/bin/.

To omit the Kudu unit tests during the build, add -DNO_TESTS=1 to the invocation of cmake. For example:

$ cd build/debug
$ cmake -DNO_TESTS=1 ../..

Running unit/functional tests

To run the Kudu unit tests, you can use the ctest command from within the build/debug directory:

$ cd build/debug
$ ctest -j8

This command will report any tests that failed, and the test logs will be written to build/debug/test-logs.

Individual tests can be run by directly invoking the test binaries in build/debug/bin. Since Kudu uses the Google C++ Test Framework (gtest), specific test cases can be run with gtest flags:

# List all the tests within a test binary, then run a single test
$ build/debug/bin/tablet-test --gtest_list_tests
$ build/debug/bin/tablet-test --gtest_filter=TestTablet/9.TestFlush

gtest also allows more complex filtering patterns. See the upstream documentation for more details.

Running tests with the clang AddressSanitizer enabled

AddressSanitizer is a nice clang feature which can detect many types of memory errors. The Jenkins setup for kudu runs these tests automatically on a regular basis, but if you make large changes it can be a good idea to run it locally before pushing. To do so, you’ll need to build using clang:

$ mkdir -p build/asan
$ cd build/asan
$ CC=../../thirdparty/clang-toolchain/bin/clang \
  CXX=../../thirdparty/clang-toolchain/bin/clang++ \
  ./../thirdparty/installed/common/bin/cmake \
  -DKUDU_USE_ASAN=1 ../..
$ make -j8
$ ctest -j8

The tests will run significantly slower than without ASAN enabled, and if any memory error occurs, the test that triggered it will fail. You can then use a command like:

$ cd build/asan
$ ctest -R failing-test

to run just the failed test.

Note	For more information on AddressSanitizer, please see the ASAN web page.

Running tests with the clang Undefined Behavior Sanitizer (UBSAN) enabled

Similar to the above, you can use a special set of clang flags to enable the Undefined Behavior Sanitizer. This will generate errors on certain pieces of code which may not themselves crash but rely on behavior which isn’t defined by the C++ standard (and thus are likely bugs). To enable UBSAN, follow the same directions as for ASAN above, but pass the -DKUDU_USE_UBSAN=1 flag to the cmake invocation.

In order to get a stack trace from UBSan, you can use gdb on the failing test, and set a breakpoint as follows:

(gdb) b __ubsan::Diag::~Diag

Then, when the breakpoint fires, gather a backtrace as usual using the bt command.

Running tests with ThreadSanitizer enabled

ThreadSanitizer (TSAN) is a feature of recent Clang and GCC compilers which can detect improperly synchronized access to data along with many other threading bugs. To enable TSAN, pass -DKUDU_USE_TSAN=1 to the cmake invocation, recompile, and run tests. For example:

$ mkdir -p build/tsan
$ cd build/tsan
$ CC=../../thirdparty/clang-toolchain/bin/clang \
    CXX=../../thirdparty/clang-toolchain/bin/clang++ \
    ../../thirdparty/installed/common/bin/cmake \
    -DKUDU_USE_TSAN=1 ../..
$ make -j8
$ ctest -j8

TSAN may truncate a few lines of the stack trace when reporting where the error is. This can be bewildering. It’s documented for TSANv1 here: http://code.google.com/p/data-race-test/wiki/ThreadSanitizerAlgorithm It is not mentioned in the documentation for TSANv2, but has been observed. In order to find out what is really happening, set a breakpoint on the TSAN report in GDB using the following incantation:

$ gdb -ex 'set disable-randomization off' -ex 'b __tsan::PrintReport' ./some-test

Generating code coverage reports

In order to generate a code coverage report, you must use the following flags:

$ mkdir -p build/coverage
$ cd build/coverage
$ CC=../../thirdparty/clang-toolchain/bin/clang \
  CXX=../../thirdparty/clang-toolchain/bin/clang++ \
  cmake -DKUDU_GENERATE_COVERAGE=1 ../..
$ make -j4
$ ctest -j4

This will generate the code coverage files with extensions .gcno and .gcda. You can then use a tool like gcovr or llvm-cov gcov to visualize the results. For example, using gcovr:

$ cd build/coverage
$ mkdir cov_html
$ ../../thirdparty/installed/common/bin/gcovr \
      --gcov-executable=$(pwd)/../../build-support/llvm-gcov-wrapper \
      --html --html-details -o cov_html/coverage.html

Then open cov_html/coverage.html in your web browser.

Running lint checks

Kudu uses cpplint.py from Google to enforce coding style guidelines. You can run the lint checks via cmake using the ilint target:

$ make ilint

This will scan any file which is dirty in your working tree, or changed since the last gerrit-integrated upstream change in your git log. If you really want to do a full scan of the source tree, you may use the lint target instead.

Running clang-tidy checks

Kudu also uses the clang-tidy tool from LLVM to enforce coding style guidelines. You can run the tidy checks via cmake using the tidy target:

$ make tidy

This will scan any changes in the latest commit in the local tree. At the time of writing, it will not scan any changes that are not locally committed.

Running include-what-you-use (IWYU) checks

Kudu uses the IWYU tool to keep the set of headers in the C++ source files consistent. For more information on what consistent means, see Why IWYU.

You can run the IWYU checks via cmake using the iwyu target:

$ make iwyu

This will scan any file which is dirty in your working tree, or changed since the last gerrit-integrated upstream change in your git log.

If you want to run against a specific file, or against all files, you can use the iwyu.py script:

$ ./build-support/iwyu.py

See the output of iwyu.py --help for details on various modes of operation.

Building Kudu documentation

Kudu’s documentation is written in asciidoc and lives in the docs subdirectory.

To build the documentation (this is primarily useful if you would like to inspect your changes before submitting them to Gerrit), use the docs target:

$ make docs

This will invoke docs/support/scripts/make_docs.sh, which requires asciidoctor to process the doc sources and produce the HTML documentation, emitted to build/docs. This script requires ruby and gem to be installed on the system path, and will attempt to install asciidoctor and other related dependencies into $HOME/.gems using bundler.

Updating the Kudu web site documentation

To update the documentation that is integrated into the Kudu web site, including Javadoc documentation, you may run the following command:

$ ./docs/support/scripts/make_site.sh

This script will use your local Git repository to check out a shallow clone of the 'gh-pages' branch and use make_docs.sh to generate the HTML documentation for the web site. It will also build the Javadoc documentation. These will be placed inside the checked-out web site, along with a tarball containing only the generated documentation (the docs/ and apidocs/ paths on the web site). Everything can be found in the build/site subdirectory.

You can proceed to commit the changes in the pages repository and send a code review for your changes. In the future, this step may be automated whenever changes are checked into the main Kudu repository.

After making changes to the gh-branch branch, follow the instructions below when you want to deploy those changes to the live web site.

Deploying changes to the Apache Kudu web site

When the documentation is updated on the gh-pages branch, or when other web site files on that branch are updated, the following procedure can be used to deploy the changes to the official Apache Kudu web site. Committers have permissions to publish changes to the live site.

git checkout gh-pages
git fetch origin
git merge --ff-only origin/gh-pages
./site_tool proof        # Check for broken links (takes a long time to run)
./site_tool publish      # Generate the static HTML for the site.
cd _publish && git push  # Update the live web site.

Note	sometimes, due to glitches with the ASF gitpubsub system, a large commit, such as a change to the docs, will not get mirrored to the live site. Adding an empty commit and doing another git push tends to fix the problem. See the git log for examples of people doing this in the past.

Improving build times

Caching build output

The kudu build is compatible with ccache. Simply install your distro’s ccache package, prepend /usr/lib/ccache to your PATH, and watch your object files get cached. Link times won’t be affected, but you will see a noticeable improvement in compilation times. You may also want to increase the size of your cache using "ccache -M new_size".

Improving linker speed

One of the major time sinks in the Kudu build is linking. GNU ld is historically quite slow at linking large C++ applications. The alternative linker gold is much better at it. It’s part of the binutils package in modern distros (try binutils-gold in older ones). To enable it, simply repoint the /usr/bin/ld symlink from ld.bfd to ld.gold.

Note that gold doesn’t handle weak symbol overrides properly (see this bug report for details). As such, it cannot be used with shared objects (see below) because it’ll cause tcmalloc’s alternative malloc implementation to be ignored.

Building Kudu with dynamic linking

Kudu can be built into shared objects, which, when used with ccache, can result in a dramatic build time improvement in the steady state. Even after a make clean in the build tree, all object files can be served from ccache. By default, debug and fastdebug will use dynamic linking, while other build types will use static linking. To enable dynamic linking explicitly, run:

$ cmake -DKUDU_LINK=dynamic ../..

Subsequent builds will create shared objects instead of archives and use them when linking the kudu binaries and unit tests. The full range of options for KUDU_LINK are static, dynamic, and auto. The default is auto and only the first letter matters for the purpose of matching.

Note	Dynamic linking is incompatible with ASAN and static linking is incompatible with TSAN.

Developing Kudu in Eclipse

Eclipse can be used as an IDE for Kudu. To generate Eclipse project files, run:

$ mkdir -p <sibling directory to source tree>
$ cd <sibling directory to source tree>
$ rm -rf CMakeCache.txt CMakeFiles/
$ cmake -G "Eclipse CDT4 - Unix Makefiles" -DCMAKE_CXX_COMPILER_ARG1=-std=c++11 <source tree>

When the Eclipse generator is run in a subdirectory of the source tree, the resulting project is incomplete. That’s why it’s recommended to use a directory that’s a sibling to the source tree. See [1] for more details.

It’s critical that CMakeCache.txt be removed prior to running the generator, otherwise the extra Eclipse generator logic (the CMakeFindEclipseCDT4.make module) won’t run and standard system includes will be missing from the generated project.

Thanks to [2], the Eclipse generator ignores the -std=c++11 definition and we must add it manually on the command line via CMAKE_CXX_COMPILER_ARG1.

By default, the Eclipse CDT indexer will index everything under the kudu/ source tree. It tends to choke on certain complicated source files within thirdparty. In CDT 8.7.0, the indexer will generate so many errors that it’ll exit early, causing many spurious syntax errors to be highlighted. In older versions of CDT, it’ll spin forever.

Either way, these complicated source files must be excluded from indexing. To do this, right click on the project in the Project Explorer and select Properties. In the dialog box, select "C/C++ Project Paths", select the Source tab, highlight "Exclusion filter: (None)", and click "Edit…​". In the new dialog box, click "Add Multiple…​". Select every subdirectory inside thirdparty except installed. Click OK all the way out and rebuild the project index by right clicking the project in the Project Explorer and selecting Index → Rebuild.

With this exclusion, the only false positives (shown as "red squigglies") that CDT presents appear to be in atomicops functions (NoBarrier_CompareAndSwap for example).

Another Eclipse annoyance stems from the "[Targets]" linked resource that Eclipse generates for each unit test. These are probably used for building within Eclipse, but one side effect is that nearly every source file appears in the indexer twice: once via a target and once via the raw source file. To fix this, simply delete the [Targets] linked resource via the Project Explorer. Doing this should have no effect on writing code, though it may affect your ability to build from within Eclipse.

1. https://cmake.org/pipermail/cmake-developers/2011-November/014153.html

2. http://public.kitware.com/Bug/view.php?id=15102

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