ClickHouse/docs/en/development/contrib.md

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71	Third-Party Libraries	A list of third-party libraries used

Third-Party Libraries Used

The list of third-party libraries:

Library name	License type
abseil-cpp	Apache
AMQP-CPP	Apache
arrow	Apache
avro	Apache
aws	Apache
aws-c-common	Apache
aws-c-event-stream	Apache
aws-checksums	Apache
base64	BSD 2-clause
boost	Boost
boringssl	BSD
brotli	MIT
capnproto	MIT
cassandra	Apache
cctz	Apache
cityhash102	MIT
cppkafka	BSD 2-clause
croaring	Apache
curl	Apache
cyrus-sasl	BSD 2-clause
double-conversion	BSD 3-clause
dragonbox	Apache
fast_float	Apache
fastops	MIT
flatbuffers	Apache
fmtlib	Unknown
gcem	Apache
googletest	BSD 3-clause
grpc	Apache
h3	Apache
hyperscan	Boost
icu	Public Domain
icudata	Public Domain
jemalloc	BSD 2-clause
krb5	MIT
libc-headers	LGPL
libcpuid	BSD 2-clause
libcxx	Apache
libcxxabi	Apache
libdivide	zLib
libfarmhash	MIT
libgsasl	LGPL
libhdfs3	Apache
libmetrohash	Apache
libpq	Unknown
libpqxx	BSD 3-clause
librdkafka	MIT
libunwind	Apache
libuv	BSD
llvm	Apache
lz4	BSD
mariadb-connector-c	LGPL
miniselect	Boost
msgpack-c	Boost
murmurhash	Public Domain
NuRaft	Apache
openldap	Unknown
orc	Apache
poco	Boost
protobuf	BSD 3-clause
rapidjson	MIT
re2	BSD 3-clause
replxx	BSD 3-clause
rocksdb	BSD 3-clause
s2geometry	Apache
sentry-native	MIT
simdjson	Apache
snappy	Public Domain
sparsehash-c11	BSD 3-clause
stats	Apache
thrift	Apache
unixodbc	LGPL
xz	Public Domain
zlib-ng	zLib
zstd	BSD

The list of third-party libraries can be obtained by the following query:

SELECT library_name, license_type, license_path FROM system.licenses ORDER BY library_name COLLATE 'en';

Example

Adding new third-party libraries and maintaining patches in third-party libraries

1. Each third-party libary must reside in a dedicated directory under the contrib/ directory of the ClickHouse repository. Avoid dumps/copies of external code, instead use Git's submodule feature to pull third-party code from an external upstream repository.
2. Submodules are listed in .gitmodule. If the external library can be used as-is, you may reference the upstream repository directly. Otherwise, i.e. the external libary requires patching/customization, create a fork of the official repository in the Clickhouse organization in GitHub.
3. In the latter case, create a branch with clickhouse/ prefix from the branch you want to integrate, e.g. clickhouse/master (for master) or clickhouse/release/vX.Y.Z (for a release/vX.Y.Z tag). The purpose of this branch is to isolate customization of the library from upstream work. For example, pulls from the upstream repository into the fork will leave all clickhouse/ branches unaffected. Submodules in contrib/ must only track clickhouse/ branches of forked third-party repositories.
4. To patch a fork of a third-party library, create a dedicated branch with clickhouse/ prefix in the fork, e.g. clickhouse/fix-some-desaster. Finally, merge the patch branch into the custom tracking branch (e.g. clickhouse/master or clickhouse/release/vX.Y.Z) using a PR.
5. Always create patches of third-party libraries with the official repository in mind. Once a PR of a patch branch to the clickhouse/ branch in the fork repository is done and the submodule version in ClickHouse's official repository is bumped, consider opening another PR from the patch branch to the upstream library repository. This ensures, that 1) the contribution has more than a single use case and importance, 2) others will also benefit from it, 3) the change will not remain a maintenance burden solely on ClickHouse developers.
6. To update a submodule with changes in the upstream repository, first merge upstream master (or a new versionX.Y.Z tag) into the clickhouse-tracking branch in the fork repository. Conflicts with patches/customization will need to be resolved in this merge (see Step 4.). Once the merge is done, bump the submodule in ClickHouse to point to the new hash in the fork.