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// Check explain() results reported for a sharded cluster, in particular nscannedObjects.
// SERVER-4161
s = new ShardingTest( "explain1" , 2 , 2 );
// Tests can be invalidated by the balancer.
s.stopBalancer()
db = s.getDB( "test" );
s.adminCommand( { enablesharding : "test" } );
s.adminCommand( { shardcollection : "test.foo" , key : { _id : 1 } } );
t = db.foo;
for( i = 0; i < 10; ++i ) {
t.save( { a:i } );
}
// Without an index.
explain = t.find( { a:{ $gte:5 } } ).explain();
assert.eq( explain.cursor, 'BasicCursor' );
assert.eq( explain.n, 5 );
assert.eq( explain.nscanned, 10 );
assert.eq( explain.nscannedObjects, 10 );
// With an index.
t.ensureIndex( { a:1 } );
explain = t.find( { a:{ $gte:5 } } ).explain();
assert.eq( explain.cursor, 'BtreeCursor a_1' );
assert.eq( explain.n, 5 );
assert.eq( explain.nscanned, 5 );
assert.eq( explain.nscannedObjects, 5 );
// With a covered index.
t.ensureIndex( { a:1 } );
explain = t.find( { a:{ $gte:5 } }, { _id:0, a:1 } ).explain();
assert.eq( explain.cursor, 'BtreeCursor a_1' );
assert.eq( explain.n, 5 );
assert.eq( explain.nscanned, 5 );
assert.eq( explain.nscannedObjects, 5 ); // Covered indexes do not work with sharding.
s.stop();
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