/**
* This methods checks if rewrite can be applied using the index and also verifies all conditions
* of the operator tree.
*
* @param topOp - TableScanOperator for a single the operator tree branch
* @param indexes - Map of a table and list of indexes on it
* @return - true if rewrite can be applied on the current branch; false otherwise
* @throws SemanticException
*/
private boolean checkIfRewriteCanBeApplied(
TableScanOperator topOp, Table baseTable, Map<Table, List<Index>> indexes)
throws SemanticException {
boolean canApply = false;
// Context for checking if this optimization can be applied to the input query
RewriteCanApplyCtx canApplyCtx = RewriteCanApplyCtx.getInstance(parseContext);
Map<String, Operator<? extends Serializable>> topOps = parseContext.getTopOps();
canApplyCtx.setBaseTableName(baseTableName);
canApplyCtx.populateRewriteVars(topOp);
Map<Index, Set<String>> indexTableMap = getIndexToKeysMap(indexes.get(baseTable));
Iterator<Index> indexMapItr = indexTableMap.keySet().iterator();
Index index = null;
while (indexMapItr.hasNext()) {
// we rewrite the original query using the first valid index encountered
// this can be changed if we have a better mechanism to
// decide which index will produce a better rewrite
index = indexMapItr.next();
canApply = canApplyCtx.isIndexUsableForQueryBranchRewrite(index, indexTableMap.get(index));
if (canApply) {
canApply = checkIfAllRewriteCriteriaIsMet(canApplyCtx);
// break here if any valid index is found to apply rewrite
if (canApply) {
// check if aggregation function is set.
// If not, set it using the only indexed column
if (canApplyCtx.getAggFunction() == null) {
// strip of the start and end braces [...]
String aggregationFunction = indexTableMap.get(index).toString();
aggregationFunction =
aggregationFunction.substring(1, aggregationFunction.length() - 1);
canApplyCtx.setAggFunction("_count_of_" + aggregationFunction + "");
}
}
break;
}
}
indexTableName = index.getIndexTableName();
if (canApply && topOps.containsValue(topOp)) {
Iterator<String> topOpNamesItr = topOps.keySet().iterator();
while (topOpNamesItr.hasNext()) {
String topOpName = topOpNamesItr.next();
if (topOps.get(topOpName).equals(topOp)) {
tsOpToProcess.put(topOpName, canApplyCtx);
}
}
}
if (tsOpToProcess.size() == 0) {
canApply = false;
} else {
canApply = true;
}
return canApply;
}
