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https://github.com/ClickHouse/ClickHouse.git
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77 lines
2.1 KiB
C++
77 lines
2.1 KiB
C++
#include <Common/SipHash.h>
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#include <Common/FieldVisitors.h>
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#include <Parsers/ASTLiteral.h>
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#include <IO/WriteHelpers.h>
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#include <IO/WriteBufferFromString.h>
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#include <IO/Operators.h>
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namespace DB
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{
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void ASTLiteral::updateTreeHashImpl(SipHash & hash_state) const
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{
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const char * prefix = "Literal_";
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hash_state.update(prefix, strlen(prefix));
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applyVisitor(FieldVisitorHash(hash_state), value);
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}
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/// Writes 'tuple' word before tuple literals for backward compatibility reasons.
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/// TODO: remove, when versions lower than 20.3 will be rarely used.
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class FieldVisitorToColumnName : public StaticVisitor<String>
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{
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public:
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template<typename T>
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String operator() (const T & x) const { return visitor(x); }
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private:
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FieldVisitorToString visitor;
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};
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template<>
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String FieldVisitorToColumnName::operator() (const Tuple & x) const
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{
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WriteBufferFromOwnString wb;
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wb << "tuple(";
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for (auto it = x.begin(); it != x.end(); ++it)
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{
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if (it != x.begin())
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wb << ", ";
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wb << applyVisitor(*this, *it);
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}
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wb << ')';
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return wb.str();
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}
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void ASTLiteral::appendColumnNameImpl(WriteBuffer & ostr) const
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{
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/// 100 - just arbitrary value.
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constexpr auto min_elements_for_hashing = 100;
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/// Special case for very large arrays. Instead of listing all elements, will use hash of them.
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/// (Otherwise column name will be too long, that will lead to significant slowdown of expression analysis.)
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/// TODO: Also do hashing for large tuples, when versions lower than 20.3 will be rarely used, because it breaks backward compatibility.
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auto type = value.getType();
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if ((type == Field::Types::Array && value.get<const Array &>().size() > min_elements_for_hashing))
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{
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SipHash hash;
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applyVisitor(FieldVisitorHash(hash), value);
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UInt64 low, high;
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hash.get128(low, high);
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writeCString("__array_", ostr);
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writeText(low, ostr);
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ostr.write('_');
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writeText(high, ostr);
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}
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else
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{
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String column_name = applyVisitor(FieldVisitorToColumnName(), value);
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writeString(column_name, ostr);
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}
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}
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}
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