// We are in the join operator now.
SkewJoinOptProcCtx ctx = (SkewJoinOptProcCtx) procCtx;
parseContext = ctx.getpGraphContext();
JoinOperator joinOp = (JoinOperator)nd;
// This join has already been processed
if (ctx.getDoneJoins().contains(joinOp)) {
return null;
}
ctx.getDoneJoins().add(joinOp);
Operator<? extends OperatorDesc> currOp = joinOp;
boolean processSelect = false;
// Is there a select following
// Clone the select also. It is useful for a follow-on optimization where the union
// followed by a select star is completely removed.
if ((joinOp.getChildOperators().size() == 1) &&
(joinOp.getChildOperators().get(0) instanceof SelectOperator)) {
currOp = joinOp.getChildOperators().get(0);
processSelect = true;
}
List<TableScanOperator> tableScanOpsForJoin = new ArrayList<TableScanOperator>();
if (!getTableScanOpsForJoin(joinOp, tableScanOpsForJoin)) {
return null;
}
if ((tableScanOpsForJoin == null) || (tableScanOpsForJoin.isEmpty())) {
return null;
}
// Get the skewed values in all the tables
Map<List<ExprNodeDesc>, List<List<String>>> skewedValues =
getSkewedValues(joinOp, tableScanOpsForJoin);
// If there are no skewed values, nothing needs to be done
if (skewedValues == null || skewedValues.size() == 0) {
return null;
}
// After this optimization, the tree should be like:
// TS -> (FIL "skewed rows") * -> RS -
// \
// -> JOIN
// / \
// TS -> (FIL "skewed rows") * -> RS - \
// \
// -> UNION -> ..
// /
// TS -> (FIL "no skewed rows") * -> RS - /
// \ /
// -> JOIN
// /
// TS -> (FIL "no skewed rows") * -> RS -
//
// Create a clone of the operator
Operator<? extends OperatorDesc> currOpClone;
try {
currOpClone = currOp.clone();
insertRowResolvers(currOp, currOpClone, ctx);
} catch (CloneNotSupportedException e) {
LOG.debug("Operator tree could not be cloned");
return null;
}
// have to create a QBJoinTree for the cloned join operator
QBJoinTree originJoinTree = parseContext.getJoinContext().get(joinOp);
QBJoinTree newJoinTree;
try {
newJoinTree = originJoinTree.clone();
} catch (CloneNotSupportedException e) {
LOG.debug("QBJoinTree could not be cloned: ", e);
return null;
}
JoinOperator joinOpClone;
if (processSelect) {
joinOpClone = (JoinOperator)(currOpClone.getParentOperators().get(0));
} else {
joinOpClone = (JoinOperator)currOpClone;
}