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TreeStatePair.java
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/
TreeStatePair.java
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/*
* Copyright (c) 2002-2016 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.index.gbptree;
import org.apache.commons.lang3.tuple.Pair;
import java.io.IOException;
import java.util.Optional;
import org.neo4j.io.pagecache.PageCursor;
class TreeStatePair
{
static Pair<TreeState,TreeState> readStatePages( PageCursor cursor, long pageIdA, long pageIdB ) throws IOException
{
TreeState stateA;
TreeState stateB;
// Use write lock to avoid should retry. Fine because there can be no concurrency at this point anyway
PageCursorUtil.goTo( cursor, "state page A", pageIdA );
stateA = TreeState.read( cursor );
PageCursorUtil.goTo( cursor, "state page B", pageIdB );
stateB = TreeState.read( cursor );
return Pair.of( stateA, stateB );
}
static TreeState selectNewestValidState( Pair<TreeState,TreeState> states )
{
return selectNewestValidStateOptionally( states ).orElseThrow( () ->
new TreeInconsistencyException( "Unexpected combination of state.%n STATE_A[%s]%n STATE_B[%s]",
states.getLeft(), states.getRight() ) );
}
static TreeState selectOldestOrInvalid( Pair<TreeState,TreeState> states )
{
TreeState newestValidState = selectNewestValidStateOptionally( states ).orElse( states.getRight() );
return newestValidState == states.getLeft() ? states.getRight() : states.getLeft();
}
private static Optional<TreeState> selectNewestValidStateOptionally( Pair<TreeState,TreeState> states )
{
TreeState stateA = states.getLeft();
TreeState stateB = states.getRight();
if ( stateA.isValid() != stateB.isValid() )
{
// return only valid
return stateA.isValid() ? Optional.of( stateA ) : Optional.of( stateB );
}
else if ( stateA.isValid() && stateB.isValid() )
{
// return newest
if ( stateA.stableGeneration() > stateB.stableGeneration() &&
stateA.unstableGeneration() > stateB.unstableGeneration() )
{
return Optional.of( stateA );
}
else if ( stateA.stableGeneration() < stateB.stableGeneration() &&
stateA.unstableGeneration() < stateB.unstableGeneration() )
{
return Optional.of( stateB );
}
}
// return null communicating that this combination didn't result in any valid "newest" state
return Optional.empty();
}
}