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https://github.com/ClickHouse/ClickHouse.git
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69 lines
2.3 KiB
C++
69 lines
2.3 KiB
C++
#include <IO/ReadBufferFromFile.h>
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#include <IO/WriteBufferFromFile.h>
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#include <Common/Stopwatch.h>
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#include <Poco/File.h>
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#include <iostream>
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#include <iomanip>
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#include <vector>
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#include <algorithm>
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/** We test the hypothesis that skipping unnecessary parts of seek-forward never degrades overall read speed.
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* Before the measurements, it is desirable to discard disk cache: `echo 3 > /proc/sys/vm/drop_caches`.
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*
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* Result: yes, even frequent relatively short seek forward does not worsen anything on all tested parameters
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* - 1MiB of data, 16 0 0 16 vs 16 16 32 16
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* - 1GiB of data, 1048576 0 0 vs 1048576 512 1024 vs 1048576 1048576 1048576
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* - 1GiB of data, 1024 0 0 vs 1024 512 1024
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*/
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int main(int argc, const char ** argv)
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{
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if (argc < 5 || argc > 6)
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{
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std::cerr << "Usage:\n"
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<< argv[0] << " file bytes_in_block min_skip_bytes max_skip_bytes [buffer_size]" << std::endl;
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return 0;
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}
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int block = atoi(argv[2]);
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int min_skip = atoi(argv[3]);
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int max_skip = atoi(argv[4]);
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size_t buf_size = argc <= 5 ? DBMS_DEFAULT_BUFFER_SIZE : static_cast<size_t>(atoi(argv[5]));
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UInt64 size = Poco::File(argv[1]).getSize();
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UInt64 pos = 0;
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DB::ReadBufferFromFile in(argv[1], buf_size);
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char * buf = new char[block];
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int checksum = 0;
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UInt64 bytes_read = 0;
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Stopwatch watch;
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while (!in.eof())
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{
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UInt64 len = static_cast<UInt64>(rand() % (max_skip - min_skip + 1) + min_skip);
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len = std::min(len, size - pos);
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off_t seek_res = in.seek(len, SEEK_CUR);
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pos += len;
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if (seek_res != static_cast<off_t>(pos))
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{
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std::cerr << "Unexpected seek return value: " << seek_res << "; expeted " << pos << ", seeking by " << len << std::endl;
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return 1;
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}
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len = std::min(static_cast<UInt64>(block), size - pos);
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in.read(&buf[0], len);
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checksum += buf[0] + buf[block - 1];
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pos += len;
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bytes_read += len;
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}
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watch.stop();
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std::cout << checksum << std::endl; /// don't optimize
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std::cout << "Read " << bytes_read << " out of " << size << " bytes in "
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<< std::setprecision(4) << watch.elapsedSeconds() << " seconds ("
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<< bytes_read / watch.elapsedSeconds() / 1000000 << " MB/sec.)" << std::endl;
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return 0;
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}
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