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// Test to make sure that a reverse cursor can correctly handle empty extents (SERVER-6980)
// Create a collection with three small extents
db.jstests_reversecursor.drop();
db.runCommand({"create": "jstests_reversecursor", $nExtents: [4096, 4096, 4096]});
// Function to check whether all three extents are non empty
function extentsSpanned() {
var extents = db.jstests_reversecursor.validate(true).extents;
return (extents[0].firstRecord != "null" && extents[1].firstRecord != "null" &&
extents[2].firstRecord != "null");
}
// Insert enough documents to span all three extents
a = 0;
while (!extentsSpanned()) {
db.jstests_reversecursor.insert({a: a++});
}
// Delete all the elements in the middle
db.jstests_reversecursor.remove({a: {$gt: 0, $lt: a - 1}});
// Make sure the middle extent is empty and that both end extents are not empty
assert.eq(db.jstests_reversecursor.validate(true).extents[1].firstRecord, "null");
assert.eq(db.jstests_reversecursor.validate(true).extents[1].lastRecord, "null");
assert.neq(db.jstests_reversecursor.validate(true).extents[0].firstRecord, "null");
assert.neq(db.jstests_reversecursor.validate(true).extents[0].lastRecord, "null");
assert.neq(db.jstests_reversecursor.validate(true).extents[2].firstRecord, "null");
assert.neq(db.jstests_reversecursor.validate(true).extents[2].lastRecord, "null");
// Make sure that we get the same number of elements for both the forward and reverse cursors
assert.eq(db.jstests_reversecursor.find().sort({$natural: 1}).toArray().length, 2);
assert.eq(db.jstests_reversecursor.find().sort({$natural: -1}).toArray().length, 2);
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