/// <summary>
/// Tries to assign compound indexes to expressions if applicable...
/// </summary>
private static List <ProxyAndPredicate> AssignCompoundIndices(ProxyAndPredicate set,
IEnumerable <IIndex> indexes, IQueryStore queryStore)
{
var attribExprList = new OrderedList <string, ComparisonPredicate>();
var proxyPredicates = new List <ProxyAndPredicate>();
//For every expression in the set ready for assignment.
foreach (var expresson in set.TreePredicates)
{
var expression = (ComparisonPredicate)expresson;
if (expression.IsBinaryExpression)
{
continue;
}
attribExprList.Add(expression.AttributeNames[0], expression);
}
//Each compound index will create a new state of the expression.
foreach (var index in indexes)
{
int matchedNumber = 0;
var matchedAttribs = new List <string>();
//If keys (attributes list) does not contain the first prefix of the index
//Then the index is not usable.
if (attribExprList.ContainsKey(index.Attributes.Name))
{
matchedAttribs.Add(index.Attributes.Name);
matchedNumber += attribExprList[index.Attributes.Name].Count;
}
//if matched attributes are < 2 no need of compound assignment.
if (matchedAttribs.Count < 2)
{
continue;
}
//Assign each of them an index and get them to the predicate, and get the one with the lowest cost.
ComparisonPredicate cheapestExpression = attribExprList[matchedAttribs[0]][0];
IPredicate cheapestPredicate = cheapestExpression.AssignIndexPredicate(index, queryStore);
for (int i = 1; i < attribExprList[matchedAttribs[0]].Count; i++)
{
ComparisonPredicate tempExpression = attribExprList[matchedAttribs[0]][i];
IPredicate tempPredicate = tempExpression.AssignIndexPredicate(index, queryStore);
if (tempPredicate.Statistics[Statistic.ExpectedIO] <
cheapestPredicate.Statistics[Statistic.ExpectedIO])
{
cheapestExpression = tempExpression;
cheapestPredicate = tempPredicate;
}
}
//For filteration and adding rest of expressions to the index.
ITreePredicate assingedExpression = null;
if (!matchedNumber.Equals(2))
{
AndTreePredicate assingedAnd = new AndTreePredicate();
foreach (var attribute in matchedAttribs)
{
foreach (var expression in attribExprList[attribute])
{
if (expression != cheapestExpression)
{
assingedAnd.Add(expression);
}
}
}
assingedExpression = assingedAnd;
}
else
{
foreach (var expression in attribExprList[matchedAttribs[1]])
{
assingedExpression = expression;
}
}
FilterPredicate filterPredicate = new FilterPredicate(assingedExpression, index);
filterPredicate.AddChildPredicate(cheapestPredicate);
ProxyAndPredicate proxyAnd = (ProxyAndPredicate)set.Clone();
//Removing assigned expressions.
foreach (var attribute in matchedAttribs)
{
foreach (var expression in attribExprList[attribute])
{
proxyAnd.TreePredicates.Remove(expression);
}
}
proxyAnd.AddChildPredicate(new ProxyPredicate(filterPredicate, null));
proxyPredicates.Add(proxyAnd);
}
foreach (var proxyAnd in proxyPredicates)
{
//Recursive call for each ProxyAndPredicate.
if (proxyAnd.TreePredicates.Count > 1)
{
var values = AssignCompoundIndices(proxyAnd, indexes, queryStore);
foreach (var value in values)
{
proxyPredicates.Add(value);
}
}
}
return(proxyPredicates);
}
