SERVER-14123 prevent the explain BSONObj from growing too large

Author: dstorch

src/mongo/db/query/explain_plan.cpp

@@ -455,8 +455,18 @@ namespace mongo {
         }
     }
 
-    void statsToBSON(const PlanStageStats& stats, BSONObjBuilder* bob) {
+    void statsToBSON(const PlanStageStats& stats,
+                     BSONObjBuilder* bob,
+                     BSONObjBuilder* topLevelBob) {
         invariant(bob);
+        invariant(topLevelBob);
+
+        // Stop as soon as the BSON object we're building exceeds 10 MB.
+        static const int kMaxStatsBSONSize = 10 * 1024 * 1024;
+        if (topLevelBob->len() > kMaxStatsBSONSize) {
+            bob->append("warning", "stats tree exceeded 10 MB");
+            return;
+        }
 
         // Common details.
         bob->append("type", stageTypeString(stats.stageType));
@@ -521,9 +531,12 @@ namespace mongo {
             // TODO: how much do we really want here?  we should separate runtime stats vs. tree
             // structure (soln tostring).
             bob->append("keyPattern", spec->keyPattern.toString());
-            bob->append("boundsVerbose", spec->indexBoundsVerbose);
             bob->appendNumber("isMultiKey", spec->isMultiKey);
 
+            // The verbose bounds can get large. Truncate to 1 MB.
+            static const int kMaxVerboseBoundsSize = 1024 * 1024;
+            bob->append("boundsVerbose", spec->indexBoundsVerbose.substr(0, kMaxVerboseBoundsSize));
+
             bob->appendNumber("yieldMovedCursor", spec->yieldMovedCursor);
             bob->appendNumber("dupsTested", spec->dupsTested);
             bob->appendNumber("dupsDropped", spec->dupsDropped);
@@ -566,11 +579,15 @@ namespace mongo {
         BSONArrayBuilder childrenBob(bob->subarrayStart("children"));
         for (size_t i = 0; i < stats.children.size(); ++i) {
             BSONObjBuilder childBob(childrenBob.subobjStart());
-            statsToBSON(*stats.children[i], &childBob);
+            statsToBSON(*stats.children[i], &childBob, topLevelBob);
         }
         childrenBob.doneFast();
     }
 
+    void statsToBSON(const PlanStageStats& stats, BSONObjBuilder* bob) {
+        statsToBSON(stats, bob, bob);
+    }
+
     BSONObj statsToBSON(const PlanStageStats& stats) {
         BSONObjBuilder bob;
         statsToBSON(stats, &bob);

src/mongo/db/query/explain_plan.h

@@ -85,6 +85,10 @@ namespace mongo {
      */
     void getPlanInfo(const QuerySolution& soln, PlanInfo** infoOut);
 
+    void statsToBSON(const PlanStageStats& stats,
+                     BSONObjBuilder* bob,
+                     BSONObjBuilder* topLevelBob);
+
     void statsToBSON(const PlanStageStats& stats, BSONObjBuilder* bob);
 
     BSONObj statsToBSON(const PlanStageStats& stats);

src/mongo/db/query/index_bounds.cpp

@@ -222,9 +222,19 @@ namespace mongo {
 
                     fieldBuilder.append(
                         static_cast<BSONArray>(intervalBuilder.arr().clientReadable()));
+
+                    // If the bounds object gets too large, truncate it.
+                    static const int kMaxBoundsSize = 1024 * 1024;
+                    if (builder.len() > kMaxBoundsSize) {
+                        intervalBuilder.doneFast();
+                        fieldBuilder.append(BSON("warning" << "bounds obj exceeds 1 MB"));
+                        fieldBuilder.doneFast();
+                        return builder.obj();
+                    }
                 }
             }
         }
+
         return builder.obj();
     }