diff options
| -rw-r--r-- | src/mongo/db/exec/plan_cache_util.h | 2 | ||||
| -rw-r--r-- | src/mongo/db/query/plan_ranker_util.h | 28 | ||||
| -rw-r--r-- | src/mongo/db/query/plan_ranking_decision.h | 18 |
3 files changed, 13 insertions, 35 deletions
diff --git a/src/mongo/db/exec/plan_cache_util.h b/src/mongo/db/exec/plan_cache_util.h index 717f3c879ef..8f0260409d7 100644 --- a/src/mongo/db/exec/plan_cache_util.h +++ b/src/mongo/db/exec/plan_cache_util.h @@ -99,7 +99,7 @@ void updatePlanCache( // In "sometimes cache" mode, we cache unless we hit one of the special cases below. canCache = true; - if (ranking->tieForBest) { + if (ranking->tieForBest()) { // The winning plan tied with the runner-up and we're using "sometimes cache" mode. We // will not write a plan cache entry. canCache = false; diff --git a/src/mongo/db/query/plan_ranker_util.h b/src/mongo/db/query/plan_ranker_util.h index 58bcc16d3df..8818c47dd22 100644 --- a/src/mongo/db/query/plan_ranker_util.h +++ b/src/mongo/db/query/plan_ranker_util.h @@ -155,14 +155,6 @@ StatusWith<std::unique_ptr<PlanRankingDecision>> pickBestPlan( why->stats = StatsDetails{}; } - // Determine whether plans tied for the win. - if (scoresAndCandidateIndices.size() > 1U) { - double bestScore = scoresAndCandidateIndices[0].first; - double runnerUpScore = scoresAndCandidateIndices[1].first; - const double epsilon = 1e-10; - why->tieForBest = std::abs(bestScore - runnerUpScore) < epsilon; - } - // Update results in 'why' // Stats and scores in 'why' are sorted in descending order by score. auto&& stats = why->getStats<PlanStageStatsType>(); @@ -171,26 +163,6 @@ StatusWith<std::unique_ptr<PlanRankingDecision>> pickBestPlan( double score = scoresAndCandidateIndices[i].first; size_t candidateIndex = scoresAndCandidateIndices[i].second; - // We shouldn't cache the scores with the EOF bonus included, as this is just a - // tie-breaking measure for plan selection. Plans not run through the multi plan runner - // will not receive the bonus. - // - // An example of a bad thing that could happen if we stored scores with the EOF bonus - // included: - // - // Let's say Plan A hits EOF, is the highest ranking plan, and gets cached as such. On - // subsequent runs it will not receive the bonus. Eventually the plan cache feedback - // mechanism will evict the cache entry - the scores will appear to have fallen due to - // the missing EOF bonus. - // - // This raises the question, why don't we include the EOF bonus in scoring of cached plans - // as well? The problem here is that the cached plan runner always runs plans to completion - // before scoring. Queries that don't get the bonus in the multi plan runner might get the - // bonus after being run from the plan cache. - if (statTrees[candidateIndex]->common.isEOF) { - score -= eofBonus; - } - stats.candidatePlanStats.push_back(std::move(statTrees[candidateIndex])); why->scores.push_back(score); why->candidateOrder.push_back(candidateIndex); diff --git a/src/mongo/db/query/plan_ranking_decision.h b/src/mongo/db/query/plan_ranking_decision.h index b5c7cbf6f67..8e8543b98e3 100644 --- a/src/mongo/db/query/plan_ranking_decision.h +++ b/src/mongo/db/query/plan_ranking_decision.h @@ -137,6 +137,18 @@ struct PlanRankingDecision { return stdx::get<typename StatsToDetailMap<PlanStageStatsType>::Value>(stats); } + /* + * Returns true if there are at least two possible plans, and at least the top two plans + * have the same scores. + */ + bool tieForBest() const { + if (scores.size() > 1) { + const double epsilon = 1e-10; + return (std::abs(scores[0] - scores[1]) < epsilon); + } + return false; + } + // Execution stats details for each candidate plan. stdx::variant<StatsDetails, SBEStatsDetails> stats; @@ -158,11 +170,5 @@ struct PlanRankingDecision { // // Like 'candidateOrder', the contents of this array are indicies into the 'candidates' array. std::vector<size_t> failedCandidates; - - // Whether two plans tied for the win. - // - // Reading this flag is the only reliable way for callers to determine if there was a tie, - // because the scores kept inside the PlanRankingDecision do not incorporate the EOF bonus. - bool tieForBest = false; }; } // namespace mongo::plan_ranker |