4150 explain implementation checkpoint

1 files changed, 23 insertions, 0 deletions

diff --git a/jstests/explain6.js b/jstests/explain6.js
new file mode 100644
index 00000000000..cf9668c9dbb
--- /dev/null
+++ b/jstests/explain6.js
@@ -0,0 +1,23 @@
+// Test explain result count when a skip parameter is used.
+
+t = db.jstests_explain6;
+t.drop();
+
+t.save( {} );
+explain = t.find().skip( 1 ).explain( true );
+assert.eq( 0, explain.n );
+// With only one plan, the skip information is known for the plan.  This is an arbitrary
+// implementation detail, but it changes the way n is calculated.
+assert.eq( 0, explain.allPlans[ 0 ].n );
+
+t.ensureIndex( {a:1} );
+explain = t.find( {a:null,b:null} ).skip( 1 ).explain( true );
+assert.eq( 0, explain.n );
+// With multiple plans, the skip information is not known to the plan.
+assert.eq( 1, explain.allPlans[ 0 ].n );
+
+t.dropIndexes();
+explain = t.find().skip( 1 ).sort({a:1}).explain( true );
+// Skip is applied for an in memory sort.
+assert.eq( 0, explain.n );
+assert.eq( 1, explain.allPlans[ 0 ].n );