int idealOptimizable = firstLookOrder[joinPosition];
nextOptimizable = idealOptimizable;
int lookPos = numOptimizables;
int lastSwappedOpt = -1;
Optimizable nextOpt;
for (nextOpt = optimizableList.getOptimizable(nextOptimizable);
!(nextOpt.legalJoinOrder(assignedTableMap));
nextOpt = optimizableList.getOptimizable(nextOptimizable))
{
// Undo last swap, if we had one.
if (lastSwappedOpt >= 0) {
firstLookOrder[joinPosition] = idealOptimizable;
firstLookOrder[lookPos] = lastSwappedOpt;
}
if (lookPos > joinPosition + 1) {
// we still have other possibilities; get the next
// one by "swapping" it into the current position.
lastSwappedOpt = firstLookOrder[--lookPos];
firstLookOrder[joinPosition] = lastSwappedOpt;
firstLookOrder[lookPos] = idealOptimizable;
nextOptimizable = lastSwappedOpt;
}
else {
// we went through all of the available optimizables
// and none of them were legal in the current position;
// so we give up and fall back to normal processing.
// Note: we have to make sure we reload the best plans
// as we rewind since they may have been clobbered
// (as part of the current join order) before we got
// here.
if (joinPosition > 0) {
joinPosition--;
reloadBestPlan = true;
rewindJoinOrder();
}
permuteState = NO_JUMP;
break;
}
}
if (permuteState == NO_JUMP)
continue;
if (joinPosition == numOptimizables - 1) {
// we just set the final position within our
// "firstLookOrder" join order; now go ahead
// and search for the best join order, starting from
// the join order stored in "firstLookOrder". This
// is called walking "high" because we're searching
// the join orders that are at or "above" (after) the
// order found in firstLookOrder. Ex. if we had three
// optimizables and firstLookOrder was [1 2 0], then
// the "high" would be [1 2 0], [2 0 1] and [2 1 0];
// the "low" would be [0 1 2], [0 2 1], and [1 0 2].
// We walk the "high" first, then fall back and
// walk the "low".
permuteState = WALK_HIGH;
}
}
else
{
/* Find the next unused table at this join position */
nextOptimizable = proposedJoinOrder[joinPosition] + 1;
for ( ; nextOptimizable < numOptimizables; nextOptimizable++)
{
boolean found = false;
for (int posn = 0; posn < joinPosition; posn++)
{
/*
** Is this optimizable already somewhere
** in the join order?
*/
if (proposedJoinOrder[posn] == nextOptimizable)
{
found = true;
break;
}
}
/* Check to make sure that all of the next optimizable's
* dependencies have been satisfied.
*/
if (nextOptimizable < numOptimizables)
{
Optimizable nextOpt =
optimizableList.getOptimizable(nextOptimizable);
if (! (nextOpt.legalJoinOrder(assignedTableMap)))
{
if (optimizerTrace)
{
trace(SKIPPING_JOIN_ORDER, nextOptimizable, 0, 0.0, null);
}
/*
** If this is a user specified join order then it is illegal.
*/
if ( ! optimizableList.optimizeJoinOrder())
{
if (optimizerTrace)
{
trace(ILLEGAL_USER_JOIN_ORDER, 0, 0, 0.0, null);
}
throw StandardException.newException(SQLState.LANG_ILLEGAL_FORCED_JOIN_ORDER);
}
continue;
}
}
if (! found)
{
break;
}
}
}
/*
** We are going to try an optimizable at the current join order
** position. Is there one already at that position?
*/
if (proposedJoinOrder[joinPosition] >= 0)
{
/*
** We are either going to try another table at the current
** join order position, or we have exhausted all the tables
** at the current join order position. In either case, we
** need to pull the table at the current join order position
** and remove it from the join order.
*/
Optimizable pullMe =
optimizableList.getOptimizable(
proposedJoinOrder[joinPosition]);
/*
** Subtract the cost estimate of the optimizable being
** removed from the total cost estimate.
**
** The total cost is the sum of all the costs, but the total
** number of rows is the number of rows returned by the
** innermost optimizable.
*/
double prevRowCount;
double prevSingleScanRowCount;
int prevPosition = 0;
if (joinPosition == 0)
{
prevRowCount = outermostCostEstimate.rowCount();
prevSingleScanRowCount = outermostCostEstimate.singleScanRowCount();
}
else
{
prevPosition = proposedJoinOrder[joinPosition - 1];
CostEstimate localCE =
optimizableList.
getOptimizable(prevPosition).
getBestAccessPath().
getCostEstimate();
prevRowCount = localCE.rowCount();
prevSingleScanRowCount = localCE.singleScanRowCount();
}
/*
** If there is no feasible join order, the cost estimate
** in the best access path may never have been set.
** In this case, do not subtract anything from the
** current cost, since nothing was added to the current
** cost.
*/
double newCost = currentCost.getEstimatedCost();
double pullCost = 0.0;
CostEstimate pullCostEstimate =
pullMe.getBestAccessPath().getCostEstimate();
if (pullCostEstimate != null)
{
pullCost = pullCostEstimate.getEstimatedCost();
newCost -= pullCost;
/*
** It's possible for newCost to go negative here due to
** loss of precision.
*/
if (newCost < 0.0)
newCost = 0.0;
}
/* If we are choosing a new outer table, then
* we rest the starting cost to the outermostCost.
* (Thus avoiding any problems with floating point
* accuracy and going negative.)
*/
if (joinPosition == 0)
{
if (outermostCostEstimate != null)
{
newCost = outermostCostEstimate.getEstimatedCost();
}
else
{
newCost = 0.0;
}
}
currentCost.setCost(
newCost,
prevRowCount,
prevSingleScanRowCount);
/*
** Subtract from the sort avoidance cost if there is a
** required row ordering.
**
** NOTE: It is not necessary here to check whether the
** best cost was ever set for the sort avoidance path,
** because it considerSortAvoidancePath() would not be
** set if there cost were not set.
*/
if (requiredRowOrdering != null)
{
if (pullMe.considerSortAvoidancePath())
{
AccessPath ap = pullMe.getBestSortAvoidancePath();
double prevEstimatedCost = 0.0d;
/*
** Subtract the sort avoidance cost estimate of the
** optimizable being removed from the total sort
** avoidance cost estimate.
**
** The total cost is the sum of all the costs, but the
** total number of rows is the number of rows returned
** by the innermost optimizable.
*/
if (joinPosition == 0)
{
prevRowCount = outermostCostEstimate.rowCount();
prevSingleScanRowCount = outermostCostEstimate.singleScanRowCount();
/* If we are choosing a new outer table, then
* we rest the starting cost to the outermostCost.
* (Thus avoiding any problems with floating point
* accuracy and going negative.)
*/
prevEstimatedCost = outermostCostEstimate.getEstimatedCost();
}
else
{
CostEstimate localCE =
optimizableList.
getOptimizable(prevPosition).
getBestSortAvoidancePath().
getCostEstimate();
prevRowCount = localCE.rowCount();
prevSingleScanRowCount = localCE.singleScanRowCount();
prevEstimatedCost = currentSortAvoidanceCost.getEstimatedCost() -
ap.getCostEstimate().getEstimatedCost();
}
currentSortAvoidanceCost.setCost(
prevEstimatedCost,
prevRowCount,
prevSingleScanRowCount);
/*
** Remove the table from the best row ordering.
** It should not be necessary to remove it from
** the current row ordering, because it is
** maintained as we step through the access paths
** for the current Optimizable.
*/
bestRowOrdering.removeOptimizable(
pullMe.getTableNumber());
/*
** When removing a table from the join order,
** the best row ordering for the remaining outer tables
** becomes the starting point for the row ordering of
** the current table.
*/
bestRowOrdering.copy(currentRowOrdering);
}
}
/*
** Pull the predicates at from the optimizable and put
** them back in the predicate list.
**
** NOTE: This is a little inefficient because it pulls the
** single-table predicates, which are guaranteed to always
** be pushed to the same optimizable. We could make this
** leave the single-table predicates where they are.
*/
pullMe.pullOptPredicates(predicateList);
/*
** When we pull an Optimizable we need to go through and
** load whatever best path we found for that Optimizable
** with respect to this OptimizerImpl. The reason is that
** we could be pulling the Optimizable for the last time
** (before returning false), in which case we want it (the
** Optimizable) to be holding the best access path that it
** had at the time we found bestJoinOrder. This ensures
** that the access path which is generated and executed for
** the Optimizable matches the the access path decisions
** made by this OptimizerImpl for the best join order.
**
** NOTE: We we only reload the best plan if it's necessary
** to do so--i.e. if the best plans aren't already loaded.
** The plans will already be loaded if the last complete
** join order we had was the best one so far, because that
** means we called "rememberAsBest" on every Optimizable
** in the list and, as part of that call, we will run through
** and set trulyTheBestAccessPath for the entire subtree.
** So if we haven't tried any other plans since then,
** we know that every Optimizable (and its subtree) already
** has the correct best plan loaded in its trulyTheBest
** path field. It's good to skip the load in this case
** because 'reloading best plans' involves walking the
** entire subtree of _every_ Optimizable in the list, which
** can be expensive if there are deeply nested subqueries.
*/
if (reloadBestPlan)
pullMe.updateBestPlanMap(FromTable.LOAD_PLAN, this);
/* Mark current join position as unused */
proposedJoinOrder[joinPosition] = -1;
}
/* Have we exhausted all the optimizables at this join position? */
if (nextOptimizable >= numOptimizables)
{
/*
** If we're not optimizing the join order, remember the first
** join order.
*/
if ( ! optimizableList.optimizeJoinOrder())
{
// Verify that the user specified a legal join order
if ( ! optimizableList.legalJoinOrder(numTablesInQuery))
{
if (optimizerTrace)
{
trace(ILLEGAL_USER_JOIN_ORDER, 0, 0, 0.0, null);
}
throw StandardException.newException(SQLState.LANG_ILLEGAL_FORCED_JOIN_ORDER);
}
if (optimizerTrace)
{
trace(USER_JOIN_ORDER_OPTIMIZED, 0, 0, 0.0, null);
}
desiredJoinOrderFound = true;
}
if (permuteState == READY_TO_JUMP && joinPosition > 0 && joinPosition == numOptimizables-1)
{
permuteState = JUMPING;
/* A simple heuristics is that the row count we got indicates a potentially
* good join order. We'd like row count to get big as late as possible, so
* that less load is carried over.
*/
double rc[] = new double[numOptimizables];
for (int i = 0; i < numOptimizables; i++)
{
firstLookOrder[i] = i;
CostEstimate ce = optimizableList.getOptimizable(i).
getBestAccessPath().getCostEstimate();
if (ce == null)
{
permuteState = READY_TO_JUMP; //come again?
break;
}
rc[i] = ce.singleScanRowCount();
}
if (permuteState == JUMPING)
{
boolean doIt = false;
int temp;
for (int i = 0; i < numOptimizables; i++) //simple selection sort
{
int k = i;
for (int j = i+1; j < numOptimizables; j++)
if (rc[j] < rc[k]) k = j;
if (k != i)
{
rc[k] = rc[i]; //destroy the bridge
temp = firstLookOrder[i];
firstLookOrder[i] = firstLookOrder[k];
firstLookOrder[k] = temp;
doIt = true;
}
}
if (doIt)
{
joinPosition--;
rewindJoinOrder(); //jump from ground
continue;
}
else permuteState = NO_JUMP; //never
}
}
/*
** We have exhausted all the optimizables at this level.
** Go back up one level.
*/
/* Go back up one join position */
joinPosition--;
/* Clear the assigned table map for the previous position
* NOTE: We need to do this here to for the dependency tracking
*/
if (joinPosition >= 0)
{
Optimizable pullMe =
optimizableList.getOptimizable(
proposedJoinOrder[joinPosition]);
/*
** Clear the bits from the table at this join position.
** This depends on them having been set previously.
** NOTE: We need to do this here to for the dependency tracking
*/
assignedTableMap.xor(pullMe.getReferencedTableMap());
}
if (joinPosition < 0 && permuteState == WALK_HIGH) //reached peak
{
joinPosition = 0; //reset, fall down the hill
permuteState = WALK_LOW;
}
continue;
}
/*
** We have found another optimizable to try at this join position.
*/
proposedJoinOrder[joinPosition] = nextOptimizable;
if (permuteState == WALK_LOW)
{
boolean finishedCycle = true;
for (int i = 0; i < numOptimizables; i++)
{
if (proposedJoinOrder[i] < firstLookOrder[i])
{
finishedCycle = false;
break;
}
else if (proposedJoinOrder[i] > firstLookOrder[i]) //done
break;
}
if (finishedCycle)
{
// We just set proposedJoinOrder[joinPosition] above, so
// if we're done we need to put it back to -1 to indicate
// that it's an empty slot. Then we rewind and pull any
// other Optimizables at positions < joinPosition.
// Note: we have to make sure we reload the best plans
// as we rewind since they may have been clobbered
// (as part of the current join order) before we got
// here.
proposedJoinOrder[joinPosition] = -1;
joinPosition--;
if (joinPosition >= 0)
{
reloadBestPlan = true;
rewindJoinOrder();
joinPosition = -1;
}
permuteState = READY_TO_JUMP;
endOfRoundCleanup();
return false;
}
}
/* Re-init (clear out) the cost for the best access path
* when placing a table.
*/
optimizableList.getOptimizable(nextOptimizable).
getBestAccessPath().setCostEstimate((CostEstimate) null);
/* Set the assigned table map to be exactly the tables
* in the current join order.
*/
assignedTableMap.clearAll();
for (int index = 0; index <= joinPosition; index++)
{
assignedTableMap.or(optimizableList.getOptimizable(proposedJoinOrder[index]).getReferencedTableMap());
}
if (optimizerTrace)
{
trace(CONSIDERING_JOIN_ORDER, 0, 0, 0.0, null);
}
Optimizable nextOpt =
optimizableList.getOptimizable(nextOptimizable);
nextOpt.startOptimizing(this, currentRowOrdering);
pushPredicates(
optimizableList.getOptimizable(nextOptimizable),
assignedTableMap);