Github user zellerh commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1051#discussion_r111432560
--- Diff: core/sql/optimizer/RelExpr.cpp ---
@@ -9055,19 +9056,33 @@ void Scan::setTableAttributes(CANodeId nodeId)
setBaseCardinality(MIN_ONE (tableDesc->getNATable()->getEstRowCount())) ;
}
-NABoolean Scan::updateableIndex(IndexDesc *idx)
+NABoolean Scan::updateableIndex(IndexDesc *idx, ValueIdSet& preds,
+ NABoolean & needsHalloweenProtection)
{
//
- // Returns TRUE if the index (idx) can be used for a scan during
- // an UPDATE. Halloween problem is protected with a sort using
- // Scan::requiresHalloweenForUpdateUsingIndexScan().
- // Returns FALSE only for certain embedded updates now.
+ // Returns TRUE if the index (idx) can be used for a scan during an
UPDATE.
+ // Returns TRUE with needsHalloweenProtection also set to TRUE, if the
index
+ // needs a blocking sort for Halloween protection
+ // Otherwise, returns FALSE to prevent use of this index.
+ // Using the index in this case requires Halloween protection, but is
likely
+ // inefficient since there are no useful preds on the index key columns,
so
+ // we don't add this index to list of candidates.
//
- if (!getGroupAttr()->isEmbeddedUpdate())
- return TRUE ;
-
+ // The conditions of when this index returns TRUE can also be expressed
as
+ // returns true for an index if it is
+ // a) a unique/clustering index or
+ // b) has a unique predicate on its key or
+ // c) has an equals or range predicate on all the index columns that
--- End diff --
Just updated the comment above to simplify the condition for when we need
Halloween protection. Checking for a unique key on _ixcols_ is not needed, all
we have to check are equality predicates on the updated columns.
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