上篇的MySQL Protocol和Read调用里介绍了ClickHouse一条查询语句的调用栈，本文继续介绍写的调用栈，开整。

Write请求

建表:1
2mysql> CREATE TABLE test(a UInt8, b UInt8, c UInt8) ENGINE=MergeTree() PARTITION BY (a, b) ORDER BY c;
Query OK, 0 rows affected (0.03 sec)
写入数据：1INSERT INTO test VALUES(1,1,1), (2,2,2);

调用栈分析

1. 获取存储引擎OutputStream

DB::StorageMergeTree::write(std::__1::shared_ptr<DB::IAST> const&, DB::Context const&) StorageMergeTree.cpp:174
DB::PushingToViewsBlockOutputStream::PushingToViewsBlockOutputStream(std::__1::shared_ptr<DB::IStorage> const&, DB::Context const&, std::__1::shared_ptr<DB::IAST> const&, bool) PushingToViewsBlockOutputStream.cpp:110
DB::InterpreterInsertQuery::execute() InterpreterInsertQuery.cpp:229
DB::executeQueryImpl(const char *, const char *, DB::Context &, bool, DB::QueryProcessingStage::Enum, bool, DB::ReadBuffer *) executeQuery.cpp:364
DB::executeQuery(DB::ReadBuffer&, DB::WriteBuffer&, bool, DB::Context&, std::__1::function<void (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)>) executeQuery.cpp:696
DB::MySQLHandler::comQuery(DB::ReadBuffer&) MySQLHandler.cpp:311
DB::MySQLHandler::run() MySQLHandler.cpp:141

2. 组装OutputStream

DB::InterpreterInsertQuery::execute() InterpreterInsertQuery.cpp:107
DB::executeQueryImpl(const char *, const char *, DB::Context &, bool, DB::QueryProcessingStage::Enum, bool, DB::ReadBuffer *) executeQuery.cpp:364
DB::executeQuery(DB::ReadBuffer&, DB::WriteBuffer&, bool, DB::Context&, std::__1::function<void (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)>) executeQuery.cpp:696
DB::MySQLHandler::comQuery(DB::ReadBuffer&) MySQLHandler.cpp:311
DB::MySQLHandler::run() MySQLHandler.cpp:141

组装顺序:

NullAndDoCopyBlockInputStream
CountingBlockOutputStream
AddingDefaultBlockOutputStream
SquashingBlockOutputStream
PushingToViewsBlockOutputStream
MergeTreeBlockOutputStream

3. 写入OutputStream

DB::MergeTreeBlockOutputStream::write(DB::Block const&) MergeTreeBlockOutputStream.cpp:17
DB::PushingToViewsBlockOutputStream::write(DB::Block const&) PushingToViewsBlockOutputStream.cpp:145
DB::SquashingBlockOutputStream::finalize() SquashingBlockOutputStream.cpp:30
DB::SquashingBlockOutputStream::writeSuffix() SquashingBlockOutputStream.cpp:50
DB::AddingDefaultBlockOutputStream::writeSuffix() AddingDefaultBlockOutputStream.cpp:25
DB::CountingBlockOutputStream::writeSuffix() CountingBlockOutputStream.h:37
DB::copyDataImpl<DB::copyData(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::atomic<bool>*)::<lambda()>&, void (&)(const DB::Block&)>(DB::IBlockInputStream &, DB::IBlockOutputStream &, <lambda()> &, void (&)(const DB::Block &)) copyData.cpp:52
DB::copyData(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::atomic<bool>*) copyData.cpp:138
DB::NullAndDoCopyBlockInputStream::readImpl() NullAndDoCopyBlockInputStream.h:57
DB::IBlockInputStream::read() IBlockInputStream.cpp:60
void DB::copyDataImpl<std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&>(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&) copyData.cpp:29
DB::copyData(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&) copyData.cpp:154
DB::executeQuery(DB::ReadBuffer&, DB::WriteBuffer&, bool, DB::Context&, std::__1::function<void (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)>) executeQuery.cpp:748
DB::MySQLHandler::comQuery(DB::ReadBuffer&) MySQLHandler.cpp:311
DB::MySQLHandler::run() MySQLHandler.cpp:141

通过copyData方法，让数据在OutputStream间层层透传，一直到MergeTreeBlockOutputStream。

4. 返回Client

DB::MySQLOutputFormat::finalize() MySQLOutputFormat.cpp:62
DB::IOutputFormat::doWriteSuffix() IOutputFormat.h:78
DB::OutputStreamToOutputFormat::writeSuffix() OutputStreamToOutputFormat.cpp:18
DB::MaterializingBlockOutputStream::writeSuffix() MaterializingBlockOutputStream.h:22
void DB::copyDataImpl<std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&>(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&) copyData.cpp:52
DB::copyData(DB::IBlockInputStream&, DB::IBlockOutputStream&, std::__1::function<bool ()> const&, std::__1::function<void (DB::Block const&)> const&) copyData.cpp:154
DB::executeQuery(DB::ReadBuffer&, DB::WriteBuffer&, bool, DB::Context&, std::__1::function<void (std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)>) executeQuery.cpp:748
DB::MySQLHandler::comQuery(DB::ReadBuffer&) MySQLHandler.cpp:311
DB::MySQLHandler::run() MySQLHandler.cpp:141

总结

INSERT INTO test VALUES(1,1,1), (2,2,2);

首先内核解析SQL语句生成AST，根据AST获取Interpreter：InterpreterInsertQuery。其次Interpreter依次添加相应的OutputStream。然后从InputStream读取数据，写入到OutputStream，stream会层层渗透，一直写到底层的存储引擎。最后写入到Socket Output，返回结果。

ClickHouse的OutputStream编排还是比较复杂，缺少类似Pipeline的调度和编排，但是由于模式比较固化，目前看还算清晰。

来源：https://bohutang.me/

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ClickHouse和他的朋友们(3)MySQL Protocol和Write调用栈