ClickHouse/dbms/src/IO/tests/o_direct_and_dirty_pages.cpp

#include <string>

#include <iostream>

#include <DB/Core/Types.h>
#include <DB/IO/WriteHelpers.h>
#include <DB/IO/ReadHelpers.h>
#include <DB/IO/WriteBufferFromFile.h>
#include <DB/IO/ReadBufferFromFile.h>

int main(int argc, char ** argv)
{
	using namespace DB;

	try
	{
		const size_t N = 100000;
		const size_t BUF_SIZE = 1048576;

		ReadBufferFromFile rand_in("/dev/urandom");
		unsigned rand = 0;
		readBinary(rand, rand_in);

		String test = "Hello, world! " + toString(rand);

        /// Write to file as usual, read with O_DIRECT.

		{
			WriteBufferFromFile wb("test1", BUF_SIZE);
			for (size_t i = 0; i < N; ++i)
				writeStringBinary(test, wb);
			wb.next();
		}

		{
			ReadBufferFromFile rb("test1", BUF_SIZE, O_RDONLY | O_DIRECT, nullptr, 4096);
			String res;
			for (size_t i = 0; i < N; ++i)
				readStringBinary(res, rb);

			std::cerr << "test: " << test << ", res: " << res << ", bytes: " << rb.count() << std::endl;
		}

        /// Write to file with O_DIRECT, read as usual.

		{
			WriteBufferFromFile wb("test2", BUF_SIZE, O_WRONLY | O_CREAT | O_TRUNC | O_DIRECT, 0666, nullptr, 4096);

			for (size_t i = 0; i < N; ++i)
				writeStringBinary(test, wb);

			if (wb.offset() % 4096 != 0)
			{
				size_t pad = 4096 - wb.offset() % 4096;
				memset(wb.position(), 0, pad);
				wb.position() += pad;
			}

			wb.next();
		}

		{
			ReadBufferFromFile rb("test2", BUF_SIZE);
			String res;
			for (size_t i = 0; i < N; ++i)
				readStringBinary(res, rb);

			std::cerr << "test: " << test << ", res: " << res << ", bytes: " << rb.count() << std::endl;
		}
	}
	catch (const Exception & e)
	{
		std::cerr << e.what() << ", " << e.displayText() << std::endl;
		return 1;
	}

	return 0;
}