1 files changed, 80 insertions, 0 deletions
diff --git a/jstests/libs/analyze_plan.js b/jstests/libs/analyze_plan.js
new file mode 100644
index 00000000000..9c2ebffd890
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+++ b/jstests/libs/analyze_plan.js
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+// Contains helpers for checking, based on the explain output, properties of a
+// plan. For instance, there are helpers for checking whether a plan is a collection
+// scan or whether the plan is covered (index only).
+
+/**
+ * Given the root stage of explain's BSON representation of a query plan ('root'),
+ * returns true if the plan has a stage called 'stage'.
+ */
+function planHasStage(root, stage) {
+    if (root.stage === stage) {
+        return true;
+    }
+    else if ("inputStage" in root) {
+        return planHasStage(root.inputStage, stage);
+    }
+    else if ("inputStages" in root) {
+        for (var i = 0; i < root.inputStages.length; i++) {
+            if (planHasStage(root.inputStages[i], stage)) {
+                return true;
+            }
+        }
+    }
+
+    return false;
+}
+
+/**
+ * A query is covered iff it does *not* have a FETCH stage or a COLLSCAN.
+ *
+ * Given the root stage of explain's BSON representation of a query plan ('root'),
+ * returns true if the plan is index only. Otherwise returns false.
+ */
+function isIndexOnly(root) {
+    return !planHasStage(root, "FETCH") && !planHasStage(root, "COLLSCAN");
+}
+
+/**
+ * Returns true if the BSON representation of a plan rooted at 'root' is using
+ * an index scan, and false otherwise.
+ */
+function isIxscan(root) {
+    return planHasStage(root, "IXSCAN");
+}
+
+/**
+ * Returns true if the BSON representation of a plan rooted at 'root' is using
+ * the idhack fast path, and false otherwise.
+ */
+function isIdhack(root) {
+    return planHasStage(root, "IDHACK");
+}
+
+/**
+ * Returns true if the BSON representation of a plan rooted at 'root' is using
+ * a collection scan, and false otherwise.
+ */
+function isCollscan(root) {
+    return planHasStage(root, "COLLSCAN");
+}
+
+/**
+ * Get the number of chunk skips for the BSON exec stats tree rooted at 'root'.
+ */
+function getChunkSkips(root) {
+    if (root.stage === "SHARDING_FILTER") {
+        return root.chunkSkips;
+    }
+    else if ("inputStage" in root) {
+        return getChunkSkips(root.inputStage);
+    }
+    else if ("inputStages" in root) {
+        var skips = 0;
+        for (var i = 0; i < root.inputStages.length; i++) {
+            skips += getChunkSkips(root.inputStages[0]);
+        }
+        return skips;
+    }
+
+    return 0;
+}