1 files changed, 132 insertions, 0 deletions
diff --git a/jstests/replsets/explain_slaveok.js b/jstests/replsets/explain_slaveok.js
new file mode 100644
index 00000000000..311a374fc97
--- /dev/null
+++ b/jstests/replsets/explain_slaveok.js
@@ -0,0 +1,132 @@
+// Test the explain command on the primary and on secondaries:
+//
+// 1) Explain of read operations should work on the secondaries iff slaveOk is set.
+//
+// 2) Explain of write operations should
+//     --fail on secondaries, even if slaveOk is set,
+//     --succeed on primary without applying any writes.
+
+var name = "explain_slaveok";
+
+print("Start replica set with two nodes");
+var replTest = new ReplSetTest({name: name, nodes: 2});
+var nodes = replTest.startSet();
+replTest.initiate();
+var primary = replTest.getMaster();
+
+// Insert a document and let it sync to the secondary.
+print("Initial sync");
+primary.getDB("test").explain_slaveok.insert({a: 1});
+replTest.awaitReplication();
+
+// Check that the document is present on the primary.
+assert.eq(1, primary.getDB("test").explain_slaveok.findOne({a: 1})["a"]);
+
+// We shouldn't be able to read from the secondary with slaveOk off.
+var secondary = replTest.getSecondary();
+secondary.getDB("test").getMongo().setSlaveOk(false);
+assert.throws(function() {
+    secondary.getDB("test").explain_slaveok.findOne({a: 1});
+});
+
+// With slaveOk on, we should be able to read from the secondary.
+secondary.getDB("test").getMongo().setSlaveOk(true);
+assert.eq(1, secondary.getDB("test").explain_slaveok.findOne({a: 1})["a"]);
+
+//
+// Test explains on primary.
+//
+
+// Explain a count on the primary.
+var explainOut = primary.getDB("test").runCommand({
+    explain: {
+        count: "explain_slaveok",
+        query: {a: 1}
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandWorked(explainOut, "explain read op on primary");
+
+// Explain an update on the primary.
+explainOut = primary.getDB("test").runCommand({
+    explain: {
+        update: "explain_slaveok",
+        updates: [
+            {q: {a: 1}, u: {$set: {a: 5}}}
+        ]
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandWorked(explainOut, "explain write op on primary");
+
+// Plan should have an update stage at its root, reporting that it would
+// modify a single document.
+var stages = explainOut.executionStats.executionStages;
+assert.eq("UPDATE", stages.stage);
+assert.eq(1, stages.nWouldModify);
+
+// Confirm that the document did not actually get modified on the primary
+// or on the secondary.
+assert.eq(1, primary.getDB("test").explain_slaveok.findOne({a: 1})["a"]);
+secondary.getDB("test").getMongo().setSlaveOk(true);
+assert.eq(1, secondary.getDB("test").explain_slaveok.findOne({a: 1})["a"]);
+
+//
+// Test explains on secondary.
+//
+
+// Explain a count on the secondary with slaveOk off. Should fail because
+// slaveOk is required for explains on a secondary.
+secondary.getDB("test").getMongo().setSlaveOk(false);
+explainOut = secondary.getDB("test").runCommand({
+    explain: {
+        count: "explain_slaveok",
+        query: {a: 1}
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandFailed(explainOut, "explain read op on secondary, slaveOk false");
+
+// Explain of count should succeed once slaveOk is true.
+secondary.getDB("test").getMongo().setSlaveOk(true);
+explainOut = secondary.getDB("test").runCommand({
+    explain: {
+        count: "explain_slaveok",
+        query: {a: 1}
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandWorked(explainOut, "explain read op on secondary, slaveOk true");
+
+// Explain an update on the secondary with slaveOk off. Should fail because
+// slaveOk is required for explains on a secondary.
+secondary.getDB("test").getMongo().setSlaveOk(false);
+explainOut = secondary.getDB("test").runCommand({
+    explain: {
+        update: "explain_slaveok",
+        updates: [
+            {q: {a: 1}, u: {$set: {a: 5}}}
+        ]
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandFailed(explainOut, "explain write op on secondary, slaveOk false");
+
+// Explain of the update should also fail with slaveOk on.
+secondary.getDB("test").getMongo().setSlaveOk(true);
+explainOut = secondary.getDB("test").runCommand({
+    explain: {
+        update: "explain_slaveok",
+        updates: [
+            {q: {a: 1}, u: {$set: {a: 5}}}
+        ]
+    },
+    verbosity: "executionStats"
+});
+printjson(explainOut);
+assert.commandFailed(explainOut, "explain write op on secondary, slaveOk true");