Revert "SERVER-41279 Eliminate failed plans from consideration during query planning"

This reverts commit 6bba6446e632b557ccc03834d4d48e90336679fc.

1 files changed, 17 insertions, 35 deletions

diff --git a/src/mongo/db/query/plan_ranker.cpp b/src/mongo/db/query/plan_ranker.cpp
index 2970428be3b..ff2e636a28a 100644
--- a/src/mongo/db/query/plan_ranker.cpp
+++ b/src/mongo/db/query/plan_ranker.cpp
@@ -65,9 +65,10 @@ using std::endl;
 using std::vector;
 
 // static
-StatusWith<std::unique_ptr<PlanRankingDecision>> PlanRanker::pickBestPlan(
-    const vector<CandidatePlan>& candidates) {
+size_t PlanRanker::pickBestPlan(const vector<CandidatePlan>& candidates, PlanRankingDecision* why) {
     invariant(!candidates.empty());
+    invariant(why);
+
     // A plan that hits EOF is automatically scored above
     // its peers. If multiple plans hit EOF during the same
     // set of round-robin calls to work(), then all such plans
@@ -88,44 +89,28 @@ StatusWith<std::unique_ptr<PlanRankingDecision>> PlanRanker::pickBestPlan(
     // Holds (score, candidateInndex).
     // Used to derive scores and candidate ordering.
     vector<std::pair<double, size_t>> scoresAndCandidateindices;
-    vector<size_t> failed;
 
     // Compute score for each tree.  Record the best.
     for (size_t i = 0; i < statTrees.size(); ++i) {
-        if (!candidates[i].failed) {
-            LOG(5) << "Scoring plan " << i << ":" << endl
-                   << redact(candidates[i].solution->toString()) << "Stats:\n"
-                   << redact(Explain::statsToBSON(*statTrees[i]).jsonString(Strict, true));
-            LOG(2) << "Scoring query plan: " << Explain::getPlanSummary(candidates[i].root)
-                   << " planHitEOF=" << statTrees[i]->common.isEOF;
-
-            double score = scoreTree(statTrees[i].get());
-            LOG(5) << "score = " << score;
-            if (statTrees[i]->common.isEOF) {
-                LOG(5) << "Adding +" << eofBonus << " EOF bonus to score.";
-                score += 1;
-            }
-
-            scoresAndCandidateindices.push_back(std::make_pair(score, i));
-        } else {
-            failed.push_back(i);
-            LOG(2) << "Not scording plan: " << Explain::getPlanSummary(candidates[i].root)
-                   << " because the plan failed.";
+        LOG(5) << "Scoring plan " << i << ":" << endl
+               << redact(candidates[i].solution->toString()) << "Stats:\n"
+               << redact(Explain::statsToBSON(*statTrees[i]).jsonString(Strict, true));
+        LOG(2) << "Scoring query plan: " << Explain::getPlanSummary(candidates[i].root)
+               << " planHitEOF=" << statTrees[i]->common.isEOF;
+
+        double score = scoreTree(statTrees[i].get());
+        LOG(5) << "score = " << score;
+        if (statTrees[i]->common.isEOF) {
+            LOG(5) << "Adding +" << eofBonus << " EOF bonus to score.";
+            score += 1;
         }
-    }
-
-    // If there isn't a viable plan we should error.
-    if (scoresAndCandidateindices.size() == 0U) {
-        return {ErrorCodes::Error(31157),
-                "No viable plan was found because all candidate plans failed."};
+        scoresAndCandidateindices.push_back(std::make_pair(score, i));
     }
 
     // Sort (scores, candidateIndex). Get best child and populate candidate ordering.
     std::stable_sort(
         scoresAndCandidateindices.begin(), scoresAndCandidateindices.end(), scoreComparator);
 
-    auto why = std::make_unique<PlanRankingDecision>();
-
     // Determine whether plans tied for the win.
     if (scoresAndCandidateindices.size() > 1U) {
         double bestScore = scoresAndCandidateindices[0].first;
@@ -139,7 +124,6 @@ StatusWith<std::unique_ptr<PlanRankingDecision>> PlanRanker::pickBestPlan(
     why->stats.clear();
     why->scores.clear();
     why->candidateOrder.clear();
-    why->failedCandidates = std::move(failed);
     for (size_t i = 0; i < scoresAndCandidateindices.size(); ++i) {
         double score = scoresAndCandidateindices[i].first;
         size_t candidateIndex = scoresAndCandidateindices[i].second;
@@ -171,11 +155,9 @@ StatusWith<std::unique_ptr<PlanRankingDecision>> PlanRanker::pickBestPlan(
         why->scores.push_back(score);
         why->candidateOrder.push_back(candidateIndex);
     }
-    for (auto& i : why->failedCandidates) {
-        why->stats.push_back(std::move(statTrees[i]));
-    }
 
-    return StatusWith<std::unique_ptr<PlanRankingDecision>>(std::move(why));
+    size_t bestChild = scoresAndCandidateindices[0].second;
+    return bestChild;
 }
 
 // TODO: Move this out.  This is a signal for ranking but will become its own complicated