private void addResult(RexNode exp) {
// Cast of literal can't be reduced, so skip those (otherwise we'd
// go into an infinite loop as we add them back).
if (exp.getKind() == RexKind.Cast) {
RexCall cast = (RexCall) exp;
RexNode operand = cast.getOperands()[0];
if (operand instanceof RexLiteral) {
return;
}
}
constExprs.add(exp);
// In the case where the expression corresponds to a UDR argument,
// we need to preserve casts. Note that this only applies to
// the topmost argument, not expressions nested within the UDR
// call.
//
// REVIEW zfong 6/13/08 - Are there other expressions where we
// also need to preserve casts?
if (parentCallTypeStack.isEmpty()) {
addCasts.add(false);
} else {
addCasts.add(
parentCallTypeStack.get(parentCallTypeStack.size() - 1)
instanceof FarragoUserDefinedRoutine);
}
}
private void reduceNotNullableFilter(
RelOptRuleCall call, FilterRel filter, RexCall rexCall, boolean reverse) {
// If the expression is a IS [NOT] NULL on a non-nullable
// column, then we can either remove the filter or replace
// it with an EmptyRel.
SqlOperator op = rexCall.getOperator();
boolean alwaysTrue;
if (op == SqlStdOperatorTable.isNullOperator
|| op == SqlStdOperatorTable.isUnknownOperator) {
alwaysTrue = false;
} else if (op == SqlStdOperatorTable.isNotNullOperator) {
alwaysTrue = true;
} else {
return;
}
if (reverse) {
alwaysTrue = !alwaysTrue;
}
RexNode operand = rexCall.getOperands()[0];
if (operand instanceof RexInputRef) {
RexInputRef inputRef = (RexInputRef) operand;
if (!inputRef.getType().isNullable()) {
if (alwaysTrue) {
call.transformTo(filter.getChild());
} else {
call.transformTo(new EmptyRel(filter.getCluster(), filter.getRowType()));
}
}
}
}
private void analyzeCall(RexCall call, Constancy callConstancy) {
parentCallTypeStack.add(call.getOperator());
// visit operands, pushing their states onto stack
super.visitCall(call);
// look for NON_CONSTANT operands
int nOperands = call.getOperands().length;
List<Constancy> operandStack = stack.subList(stack.size() - nOperands, stack.size());
for (Constancy operandConstancy : operandStack) {
if (operandConstancy == Constancy.NON_CONSTANT) {
callConstancy = Constancy.NON_CONSTANT;
}
}
// Even if all operands are constant, the call itself may
// be non-deterministic.
if (!call.getOperator().isDeterministic()) {
callConstancy = Constancy.NON_CONSTANT;
} else if (call.getOperator().isDynamicFunction()) {
// We can reduce the call to a constant, but we can't
// cache the plan if the function is dynamic
preparingStmt.disableStatementCaching();
}
// Row operator itself can't be reduced to a literal, but if
// the operands are constants, we still want to reduce those
if ((callConstancy == Constancy.REDUCIBLE_CONSTANT)
&& (call.getOperator() instanceof SqlRowOperator)) {
callConstancy = Constancy.NON_CONSTANT;
}
if (callConstancy == Constancy.NON_CONSTANT) {
// any REDUCIBLE_CONSTANT children are now known to be maximal
// reducible subtrees, so they can be added to the result
// list
for (int iOperand = 0; iOperand < nOperands; ++iOperand) {
Constancy constancy = operandStack.get(iOperand);
if (constancy == Constancy.REDUCIBLE_CONSTANT) {
addResult(call.getOperands()[iOperand]);
}
}
// if this cast expression can't be reduced to a literal,
// then see if we can remove the cast
if (call.getOperator() == SqlStdOperatorTable.castFunc) {
reduceCasts(call);
}
}
// pop operands off of the stack
operandStack.clear();
// pop this parent call operator off the stack
parentCallTypeStack.remove(parentCallTypeStack.size() - 1);
// push constancy result for this call onto stack
stack.add(callConstancy);
}
// override RexShuttle
public RexNode visitCall(final RexCall call) {
int i = reducibleExps.indexOf(call);
if (i == -1) {
return super.visitCall(call);
}
RexNode replacement = reducedValues.get(i);
if (addCasts.get(i) && (replacement.getType() != call.getType())) {
// Handle change from nullable to NOT NULL by claiming
// that the result is still nullable, even though
// we know it isn't.
//
// Also, we cannot reduce CAST('abc' AS VARCHAR(4)) to 'abc'.
// If we make 'abc' of type VARCHAR(4), we may later encounter
// the same expression in a ProjectRel's digest where it has
// type VARCHAR(3), and that's wrong.
replacement = rexBuilder.makeCast(call.getType(), replacement);
}
return replacement;
}
public void onMatch(RelOptRuleCall call) {
FilterRel filter = (FilterRel) call.rels[0];
List<RexNode> expList = new ArrayList<RexNode>(Arrays.asList(filter.getChildExps()));
RexNode newConditionExp;
boolean reduced;
if (reduceExpressions(filter, expList)) {
assert (expList.size() == 1);
newConditionExp = expList.get(0);
reduced = true;
} else {
// No reduction, but let's still test the original
// predicate to see if it was already a constant,
// in which case we don't need any runtime decision
// about filtering.
newConditionExp = filter.getChildExps()[0];
reduced = false;
}
if (newConditionExp.isAlwaysTrue()) {
call.transformTo(filter.getChild());
} else if ((newConditionExp instanceof RexLiteral)
|| RexUtil.isNullLiteral(newConditionExp, true)) {
call.transformTo(new EmptyRel(filter.getCluster(), filter.getRowType()));
} else if (reduced) {
call.transformTo(CalcRel.createFilter(filter.getChild(), expList.get(0)));
} else {
if (newConditionExp instanceof RexCall) {
RexCall rexCall = (RexCall) newConditionExp;
boolean reverse = (rexCall.getOperator() == SqlStdOperatorTable.notOperator);
if (reverse) {
rexCall = (RexCall) rexCall.getOperands()[0];
}
reduceNotNullableFilter(call, filter, rexCall, reverse);
}
return;
}
// New plan is absolutely better than old plan.
call.getPlanner().setImportance(filter, 0.0);
}
private void reduceCasts(RexCall outerCast) {
RexNode[] operands = outerCast.getOperands();
if (operands.length != 1) {
return;
}
RelDataType outerCastType = outerCast.getType();
RelDataType operandType = operands[0].getType();
if (operandType.equals(outerCastType)) {
removableCasts.add(outerCast);
return;
}
// See if the reduction
// CAST((CAST x AS type) AS type NOT NULL)
// -> CAST(x AS type NOT NULL)
// applies. TODO jvs 15-Dec-2008: consider
// similar cases for precision changes.
if (!(operands[0] instanceof RexCall)) {
return;
}
RexCall innerCast = (RexCall) operands[0];
if (innerCast.getOperator() != SqlStdOperatorTable.castFunc) {
return;
}
if (innerCast.getOperands().length != 1) {
return;
}
RelDataTypeFactory typeFactory = preparingStmt.getFarragoTypeFactory();
RelDataType outerTypeNullable = typeFactory.createTypeWithNullability(outerCastType, true);
RelDataType innerTypeNullable = typeFactory.createTypeWithNullability(operandType, true);
if (outerTypeNullable != innerTypeNullable) {
return;
}
if (operandType.isNullable()) {
removableCasts.add(innerCast);
}
}
/**
* Reduces a list of expressions.
*
* @param rel Relational expression
* @param expList List of expressions, modified in place
* @return whether reduction found something to change, and succeeded
*/
static boolean reduceExpressions(RelNode rel, List<RexNode> expList) {
RexBuilder rexBuilder = rel.getCluster().getRexBuilder();
// Find reducible expressions.
FarragoSessionPlanner planner = (FarragoSessionPlanner) rel.getCluster().getPlanner();
FarragoSessionPreparingStmt preparingStmt = planner.getPreparingStmt();
List<RexNode> constExps = new ArrayList<RexNode>();
List<Boolean> addCasts = new ArrayList<Boolean>();
List<RexNode> removableCasts = new ArrayList<RexNode>();
findReducibleExps(preparingStmt, expList, constExps, addCasts, removableCasts);
if (constExps.isEmpty() && removableCasts.isEmpty()) {
return false;
}
// Remove redundant casts before reducing constant expressions.
// If the argument to the redundant cast is a reducible constant,
// reducing that argument to a constant first will result in not being
// able to locate the original cast expression.
if (!removableCasts.isEmpty()) {
List<RexNode> reducedExprs = new ArrayList<RexNode>();
List<Boolean> noCasts = new ArrayList<Boolean>();
for (RexNode exp : removableCasts) {
RexCall call = (RexCall) exp;
reducedExprs.add(call.getOperands()[0]);
noCasts.add(false);
}
RexReplacer replacer = new RexReplacer(rexBuilder, removableCasts, reducedExprs, noCasts);
replacer.apply(expList);
}
if (constExps.isEmpty()) {
return true;
}
// Compute the values they reduce to.
List<RexNode> reducedValues = new ArrayList<RexNode>();
ReentrantValuesStmt reentrantStmt =
new ReentrantValuesStmt(
preparingStmt.getRootStmtContext(), rexBuilder, constExps, reducedValues);
FarragoSession session = getSession(rel);
reentrantStmt.execute(session, true);
if (reentrantStmt.failed) {
return false;
}
// For ProjectRel, we have to be sure to preserve the result
// types, so always cast regardless of the expression type.
// For other RelNodes like FilterRel, in general, this isn't necessary,
// and the presence of casts could hinder other rules such as sarg
// analysis, which require bare literals. But there are special cases,
// like when the expression is a UDR argument, that need to be
// handled as special cases.
if (rel instanceof ProjectRel) {
for (int i = 0; i < reducedValues.size(); i++) {
addCasts.set(i, true);
}
}
RexReplacer replacer = new RexReplacer(rexBuilder, constExps, reducedValues, addCasts);
replacer.apply(expList);
return true;
}