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46 lines
1.4 KiB
C++
46 lines
1.4 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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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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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 and tuples. 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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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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|| (type == Field::Types::Tuple && value.get<const Tuple &>().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(type == Field::Types::Array ? "__array_" : "__tuple_", 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(FieldVisitorToString(), 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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