Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1306#discussion_r152352674
--- Diff: core/sql/optimizer/IndexDesc.cpp ---
@@ -802,10 +802,30 @@ IndexProperty::compareIndexPromise(const
IndexProperty *ixProp) const
const IndexDesc * index = getIndexDesc();
const IndexDesc * otherIndex = ixProp->getIndexDesc();
- if ( ((IndexColumn
*)(index->getIndexKey()[0]).getItemExpr())->getDefinition() !=
- ((IndexColumn
*)(otherIndex->getIndexKey()[0]).getItemExpr())->getDefinition() )
-
- return INCOMPATIBLE;
+
+ // If the two indexes have differing leading columns, consider them
incompatible.
+ // For this check, we ignore the "_SALT_" column if both are salted.
+ CollIndex columnToCheck = 0;
+ NABoolean done = FALSE;
+ while (!done)
+ {
+ if (columnToCheck >= index->getIndexKey().entries())
+ return INCOMPATIBLE; // must be one of the indexes is just
"_SALT_" (seems unlikely actually)
+ else if (columnToCheck >= otherIndex->getIndexKey().entries())
+ return INCOMPATIBLE; // must be one of the indexes is just
"_SALT_" (seems unlikely actually)
+ else
+ {
+ IndexColumn * indexCol = (IndexColumn
*)(index->getIndexKey()[columnToCheck]).getItemExpr();
+ IndexColumn * otherIndexCol = (IndexColumn
*)(otherIndex->getIndexKey()[columnToCheck]).getItemExpr();
+ if ( indexCol->getNAColumn()->isSaltColumn() &&
+ otherIndexCol->getNAColumn()->isSaltColumn() )
--- End diff --
It depends. Suppose the DIVISION BY clause is on C. Should we think of ix1
as an index on C, A or just on A? If I have a query, select c from table where
c = value, then ix1 and ix2 are compatible for that query. Today,
IndexProperty::compareIndexPromise doesn't take the select predicates into
account; it is just looking for the "best" index on C. (And on A. And on B.)
---
