mongo/jstests/noPassthrough/read_majority.js

load('jstests/libs/analyze_plan.js');

(function() {
"use strict";

// This test needs its own mongod since the snapshot names must be in increasing order and once you
// have a majority commit point it is impossible to go back to not having one.
var testServer = MongoRunner.runMongod({setParameter: 'testingSnapshotBehaviorInIsolation=true'});
var db = testServer.getDB("test");
var t = db.readMajority;

function assertNoReadMajoritySnapshotAvailable() {
    var res = t.runCommand('find',
                           {batchSize: 2, readConcern: {level: "majority"}, maxTimeMS: 1000});
    assert.commandFailed(res);
    assert.eq(res.code, ErrorCodes.ExceededTimeLimit);
}

function getReadMajorityCursor() {
    var res = t.runCommand('find', {batchSize: 2, readConcern: {level: "majority"}});
    assert.commandWorked(res);
    return new DBCommandCursor(db.getMongo(), res, 2);
}

function getReadMajorityAggCursor() {
    var res = t.runCommand('aggregate', {cursor:{batchSize: 2}, readConcern: {level: "majority"}});
    assert.commandWorked(res);
    return new DBCommandCursor(db.getMongo(), res, 2);
}

function getExplainPlan(query) {
    var res = db.runCommand({explain: {find: t.getName(), filter: query}});
    return assert.commandWorked(res).queryPlanner.winningPlan;
}

//
// Actual Test
//

if (!db.serverStatus().storageEngine.supportsCommittedReads) {
    print("Skipping read_majority.js since storageEngine doesn't support it.");
    return;
}

// Ensure killOp will work on an op that is waiting for snapshots to be created
var blockedReader = startParallelShell(
        "db.readMajority.runCommand('find', {batchSize: 2, readConcern: {level: 'majority'}});",
        testServer.port);

assert.soon(function() {
    var curOps = db.currentOp(true);
    jsTestLog("curOp output: " + tojson(curOps));
    for (var i in curOps.inprog) {
        var op = curOps.inprog[i];
        if (op.op === 'query' && op.ns === "test.$cmd" && op.query.find === 'readMajority') {
            db.killOp(op.opid);
            return true;
        }
    }
    return false;
}, "could not kill an op that was waiting for a snapshot", 60 * 1000);
blockedReader();

var snapshot1 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assert.commandWorked(db.runCommand({create: "readMajority"}));
var snapshot2 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;

for (var i = 0; i < 10; i++) { assert.writeOK(t.insert({_id: i, version: 3})); }

assertNoReadMajoritySnapshotAvailable();

var snapshot3 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;

assertNoReadMajoritySnapshotAvailable();

assert.writeOK(t.update({}, {$set: {version: 4}}, false, true));
var snapshot4 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;

// Collection didn't exist in snapshot 1.
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot1}));
assertNoReadMajoritySnapshotAvailable();

// Collection existed but was empty in snapshot 2.
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot2}));
assert.eq(getReadMajorityCursor().itcount(), 0);
assert.eq(getReadMajorityAggCursor().itcount(), 0);

// In snapshot 3 the collection was filled with {version: 3} documents.
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot3}));
assert.eq(getReadMajorityAggCursor().itcount(), 10);
getReadMajorityAggCursor().forEach(function(doc) {
    // Note: agg uses internal batching so can't reliably test flipping snapshot. However, it uses
    // the same mechanism as find, so if one works, both should.
    assert.eq(doc.version, 3)
});

assert.eq(getReadMajorityCursor().itcount(), 10);
var cursor = getReadMajorityCursor(); // Note: uses batchsize=2.
assert.eq(cursor.next().version, 3);
assert.eq(cursor.next().version, 3);
assert(!cursor.objsLeftInBatch());

// In snapshot 4 the collection was filled with {version: 3} documents.
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot4}));

// This triggers a getMore which sees the new version.
assert.eq(cursor.next().version, 4);
assert.eq(cursor.next().version, 4);

// Adding an index bumps the min snapshot for a collection as of SERVER-20260. This may change to
// just filter that index out from query planning as part of SERVER-20439.
t.ensureIndex({version: 1});
assertNoReadMajoritySnapshotAvailable();

// To use the index, a snapshot created after the index was completed must be marked committed.
var newSnapshot = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assertNoReadMajoritySnapshotAvailable();
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": newSnapshot}));
assert.eq(getReadMajorityCursor().itcount(), 10);
assert.eq(getReadMajorityAggCursor().itcount(), 10);
assert(isIxscan(getExplainPlan({version: 1})));

// Dropping an index does bump the min snapshot.
t.dropIndex({version: 1});
assertNoReadMajoritySnapshotAvailable();

// To use the collection again, a snapshot created after the dropIndex must be marked committed.
newSnapshot = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assertNoReadMajoritySnapshotAvailable();
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": newSnapshot}));
assert.eq(getReadMajorityCursor().itcount(), 10);

// Reindex bumps the min snapshot.
t.reIndex();
assertNoReadMajoritySnapshotAvailable();
newSnapshot = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assertNoReadMajoritySnapshotAvailable();
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": newSnapshot}));
assert.eq(getReadMajorityCursor().itcount(), 10);

// Repair bumps the min snapshot.
db.repairDatabase();
assertNoReadMajoritySnapshotAvailable();
newSnapshot = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assertNoReadMajoritySnapshotAvailable();
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": newSnapshot}));
assert.eq(getReadMajorityCursor().itcount(), 10);
assert.eq(getReadMajorityAggCursor().itcount(), 10);

// Dropping the collection is visible in the committed snapshot, even though it hasn't been marked
// committed yet. This is allowed by the current specification even though it violates strict
// read-committed semantics since we don't guarantee them on metadata operations.
t.drop();
assert.eq(getReadMajorityCursor().itcount(), 0);
assert.eq(getReadMajorityAggCursor().itcount(), 0);

// Creating a new collection with the same name hides the collection until that operation is in the
// committed view.
t.insert({_id:0, version: 8});
assertNoReadMajoritySnapshotAvailable();
newSnapshot = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
assertNoReadMajoritySnapshotAvailable();
assert.commandWorked(db.adminCommand({"setCommittedSnapshot": newSnapshot}));
assert.eq(getReadMajorityCursor().itcount(), 1);
assert.eq(getReadMajorityAggCursor().itcount(), 1);

// Commands that only support read concern 'local', (such as ping) must work when it is explicitly
// specified and fail when 'majority' is specified.
assert.commandWorked(db.adminCommand({ping: 1, readConcern: {level: 'local'}}));
var res = assert.commandFailed(db.adminCommand({ping: 1, readConcern: {level: 'majority'}}));
assert.eq(res.code, ErrorCodes.InvalidOptions);

// Agg $out also doesn't support read concern majority.
assert.commandWorked(t.runCommand('aggregate', {pipeline: [{$out: 'out'}],
                                                readConcern: {level: 'local'}}));
var res = assert.commandFailed(t.runCommand('aggregate', {pipeline: [{$out: 'out'}],
                                                          readConcern: {level: 'majority'}}));
assert.eq(res.code, ErrorCodes.InvalidOptions);

MongoRunner.stopMongod(testServer);
}());