ClickHouse/utils/checksum-for-compressed-block/main.cpp

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#include <city.h>
#include <iostream>
#include <IO/ReadBufferFromFileDescriptor.h>
#include <IO/ReadHelpers.h>
#include <Common/hex.h>
2020-08-08 01:21:04 +00:00
/** A tool to easily prove if "Checksum doesn't match: corrupted data"
* errors are caused by random bit flips due to hardware issues.
* It frequently happens due to bad memory on network switches
* (at least about a few times a year in a fleet of ~1200 ClickHouse servers).
*
* These hardware errors don't cause any data corruption issues in ClickHouse,
* because ClickHouse always validate it's own 128 bit checksums
* and report errors if checksum doesn't match.
*
* Client can simply retry the query.
* But ops engineers want to validate if the issue is real hardware error or not.
* If checksum difference is caused by single bit flip,
* we can be sure that this is hardware error, because random bit flips
* have low probability to happen due to software bugs.
*
* Usage:
echo -ne "\x82\x6b\x00\x00\x00\x62\x00\x00\x00\xf2\x3b\x01\x00\x02\xff\xff\xff\xff\x00\x01\x01\x2c\x75\x6e\x69\x71\x49\x66\x28\x44\x65\x76\x69\x63\x65\x49\x44\x48\x61\x73\x68\x2c\x20\x65\x71\x75\x61\x6c\x73\x28\x53\x65\x73\x73\x69\x6f\x6e\x54\x79\x70\x65\x2c\x20\x30\x29\x29\x28\x41\x67\x67\x72\x65\x67\x61\x74\x65\x46\x75\x6e\x63\x74\x69\x6f\x6e\x28\x3f\x00\xf0\x03\x2c\x20\x55\x49\x6e\x74\x36\x34\x2c\x20\x55\x49\x6e\x74\x38\x29\x00\x00" | ./checksum-for-compressed-block-find-bit-flips | grep 8b40502d2ffe5b712b52e03c505ca49f
8b40502d2ffe5b712b52e03c505ca49f 32, 6
*/
std::string flipBit(std::string s, size_t pos)
{
s[pos / 8] ^= 1 << pos % 8;
return s;
}
int main(int, char **)
{
using namespace DB;
ReadBufferFromFileDescriptor in(STDIN_FILENO);
std::string str;
readStringUntilEOF(str, in);
for (size_t pos = 0; pos < str.size() * 8; ++pos)
{
auto flipped = flipBit(str, pos);
auto checksum = CityHash_v1_0_2::CityHash128(flipped.data(), flipped.size());
std::cout << getHexUIntLowercase(checksum.first) << getHexUIntLowercase(checksum.second) << "\t" << pos / 8 << ", " << pos % 8 << "\n";
}
return 0;
}