// modifies usedViews - removes all redundant views from it
internal static bool TrySimplifyJoinRewriting(ref T_Tile rewriting, T_Tile toAvoid, Dictionary <T_Tile, TileOpKind> usedViews, RewritingProcessor <T_Tile> qp)
{
RewritingSimplifier <T_Tile> simplifier = new RewritingSimplifier <T_Tile>(rewriting, toAvoid, usedViews, qp);
T_Tile simplifiedRewriting;
if (simplifier.SimplifyRewriting(out simplifiedRewriting))
{
rewriting = simplifiedRewriting;
return(true);
}
return(false);
}
public static bool RewriteQuery(T_Tile toFill, T_Tile toAvoid, out T_Tile rewriting, List <T_Tile> views, RewritingProcessor <T_Tile> qp)
{
RewritingPass <T_Tile> rewritingPass = new RewritingPass <T_Tile>(toFill, toAvoid, views, qp);
if (rewritingPass.RewriteQuery(out rewriting))
{
RewritingSimplifier <T_Tile> .TrySimplifyUnionRewriting(ref rewriting, toFill, toAvoid, qp);
return(true);
}
return(false);
}
// called for top query only
internal static bool TrySimplifyUnionRewriting(ref T_Tile rewriting, T_Tile toFill, T_Tile toAvoid, RewritingProcessor <T_Tile> qp)
{
RewritingSimplifier <T_Tile> simplifier = new RewritingSimplifier <T_Tile>(rewriting, toFill, toAvoid, qp);
// gather all unioned subqueries
T_Tile simplifiedRewriting;
if (simplifier.SimplifyRewriting(out simplifiedRewriting))
{
rewriting = simplifiedRewriting;
return(true);
}
return(false);
}
private bool RewriteQuery(out T_Tile rewriting)
{
rewriting = m_toFill;
T_Tile rewritingSoFar;
if (false == FindRewritingByIncludedAndDisjoint(out rewritingSoFar))
{
if (false == FindContributingView(out rewritingSoFar))
{
return(false);
}
}
bool hasExtraTuples = !m_qp.IsDisjointFrom(rewritingSoFar, m_toAvoid);
// try to cut off extra tuples using joins
if (hasExtraTuples)
{
foreach (T_Tile view in AvailableViews)
{
if (TryJoin(view, ref rewritingSoFar))
{
hasExtraTuples = false;
break;
}
}
}
// try to cut off extra tuples using anti-semijoins
if (hasExtraTuples)
{
foreach (T_Tile view in AvailableViews)
{
if (TryAntiSemiJoin(view, ref rewritingSoFar))
{
hasExtraTuples = false;
break;
}
}
}
if (hasExtraTuples)
{
return(false); // won't be able to cut off extra tuples
}
// remove redundant joins and anti-semijoins
RewritingSimplifier <T_Tile> .TrySimplifyJoinRewriting(ref rewritingSoFar, m_toAvoid, m_usedViews, m_qp);
// find rewriting for missing tuples, if any
T_Tile missingTuples = m_qp.AntiSemiJoin(m_toFill, rewritingSoFar);
if (!m_qp.IsEmpty(missingTuples))
{
T_Tile rewritingForMissingTuples;
if (false == RewritingPass <T_Tile> .RewriteQueryInternal(missingTuples, m_toAvoid, out rewritingForMissingTuples, m_views, new HashSet <T_Tile>(m_usedViews.Keys), m_qp))
{
rewriting = rewritingForMissingTuples;
return(false); // failure
}
else
{
// Although a more general optimization for UNIONs will handle this case,
// adding this check reduces the overall number of containment tests
if (m_qp.IsContainedIn(rewritingSoFar, rewritingForMissingTuples))
{
rewritingSoFar = rewritingForMissingTuples;
}
else
{
rewritingSoFar = m_qp.Union(rewritingSoFar, rewritingForMissingTuples);
}
}
}
// if we reached this point, we have a successful rewriting
rewriting = rewritingSoFar;
return(true);
}
