53 lines
2.2 KiB
C++
53 lines
2.2 KiB
C++
#ifndef MEMGRAPH_STORAGE_VISIBLE_HPP
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#define MEMGRAPH_STORAGE_VISIBLE_HPP
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#include "transaction/transaction.hpp"
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#include "model/record.hpp"
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#include "model/vertex.hpp"
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#include "model/edge.hpp"
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template <class T,
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class id_t,
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class lock_t>
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bool visible(const Record<T, id_t, lock_t>& r, const Transaction<id_t>& t)
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{
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// Mike Olson says 17 march 1993: the tests in this routine are correct;
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// if you think they're not, you're wrong, and you should think about it
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// again. i know, it happened to me.
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return ((r.xmin() == t.id && // inserted by the current transaction
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r.cmin() < t.cid && // before this command, and
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(r.xmax() == 0 || // the row has not been deleted, or
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(r.xmax() == t.id && // it was deleted by the current
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// transaction
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r.cmax() >= t.cid))) // but not before this command,
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|| // or
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(t.committed(r.xmin()) && // the record was inserted by a
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// committed transaction, and
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(r.xmax() > 0 || // the record has not been deleted, or
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(r.xmax() == t.id && // the row is being deleted by this
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// transaction
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r.cmax() >= t.cid) || // but it's not deleted "yet", or
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(r.xmax() != t.id && // the row was deleted by another
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// transaction
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!t.committed(r.xmax()))))); // that has not been committed
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}
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// inspects the record change history and returns the record version visible
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// to the current transaction if it exists, otherwise it returns nullptr
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template <class T,
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class id_t,
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class lock_t>
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T* max_visible(Record<T, id_t, lock_t>* record, const Transaction<id_t>& t)
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{
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// move down through the versions of the nodes until you find the first
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// one visible to this transaction
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while(record != nullptr && !visible(*record, t))
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record = record->newer();
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// if no visible nodes were found, return nullptr
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return record == nullptr ? record : &record->derived();
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}
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#endif
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