path: root/jstests/sharding/kill_pinned_cursor.js

/**
 * Run a query on a sharded cluster where one of the shards hangs. Running killCursors on the mongos
 * should always succeed.
 *
 * Uses getMore to pin an open cursor.
 * @tags: [
 *   requires_getmore,
 * ]
 */

(function() {
"use strict";

load("jstests/libs/curop_helpers.js");  // for waitForCurOpByFailPoint().

// This test manually simulates a session, which is not compatible with implicit sessions.
TestData.disableImplicitSessions = true;

const kFailPointName = "waitAfterPinningCursorBeforeGetMoreBatch";
const kFailpointOptions = {
    shouldCheckForInterrupt: true
};
const kCommandCommentString = "kill_pinned_cursor_js_test";

const st = new ShardingTest({shards: 2});
const kDBName = "test";
const mongosDB = st.s.getDB(kDBName);
const shard0DB = st.shard0.getDB(kDBName);
const shard1DB = st.shard1.getDB(kDBName);

let coll = mongosDB.jstest_kill_pinned_cursor;
coll.drop();

for (let i = 0; i < 10; i++) {
    assert.commandWorked(coll.insert({_id: i}));
}

st.shardColl(coll, {_id: 1}, {_id: 5}, {_id: 6}, kDBName, false);
st.ensurePrimaryShard(kDBName, st.shard0.name);

// The startParallelShell function will take the string it's given and serialize it into a
// string. This means that we can't pass it functions which capture variables. Instead we use
// the trick below, by putting the values for the variables we'd like to capture inside the
// string. Kudos to Dave Storch for coming up with this idea.
function makeParallelShellFunctionString(cursorId, getMoreErrCodes, useSession, sessionId) {
    let code = `const cursorId = ${cursorId.toString()};`;
    code += `const kDBName = "${kDBName}";`;
    code += `let collName = "${coll.getName()}";`;
    code += `const useSession = ${useSession};`;

    TestData.getMoreErrCodes = getMoreErrCodes;
    if (useSession) {
        TestData.sessionId = sessionId;
    }

    const runGetMore = function() {
        let getMoreCmd = {getMore: cursorId, collection: collName, batchSize: 4};

        if (useSession) {
            getMoreCmd.lsid = TestData.sessionId;
        }

        // We expect that the operation will get interrupted and fail.
        assert.commandFailedWithCode(db.runCommand(getMoreCmd), TestData.getMoreErrCodes);

        if (useSession) {
            assert.commandWorked(db.adminCommand({endSessions: [TestData.sessionId]}));
        }
    };

    code += `(${runGetMore.toString()})();`;
    return code;
}

// Tests that the various cursors involved in a sharded query can be killed, even when pinned.
//
// Sets up a sharded cursor, opens a mongos cursor, and uses failpoints to cause the mongos
// cursor to hang due to getMore commands hanging on each of the shards. Then invokes
// 'killFunc', and verifies the cursors on the shards and the mongos cursor get cleaned up.
//
// 'getMoreErrCodes' are the error codes with which we expect the getMore to fail (e.g. a
// killCursors command should cause getMore to fail with "CursorKilled", but killOp should cause
// a getMore to fail with "Interrupted").
function testShardedKillPinned(
    {killFunc: killFunc, getMoreErrCodes: getMoreErrCodes, useSession: useSession}) {
    let getMoreJoiner = null;
    let cursorId;
    let sessionId;

    try {
        // Set up the mongods to hang on a getMore request. ONLY set the failpoint on the
        // mongods. Setting the failpoint on the mongos will only cause it to spin, and not
        // actually send any requests out.
        assert.commandWorked(shard0DB.adminCommand(
            {configureFailPoint: kFailPointName, mode: "alwaysOn", data: kFailpointOptions}));
        assert.commandWorked(shard1DB.adminCommand(
            {configureFailPoint: kFailPointName, mode: "alwaysOn", data: kFailpointOptions}));

        // Run a find against mongos. This should open cursors on both of the shards.
        let findCmd = {find: coll.getName(), batchSize: 2, comment: kCommandCommentString};

        if (useSession) {
            // Manually start a session so it can be continued from inside a parallel shell.
            sessionId = assert.commandWorked(mongosDB.adminCommand({startSession: 1})).id;
            findCmd.lsid = sessionId;
        }

        let cmdRes = mongosDB.runCommand(findCmd);
        assert.commandWorked(cmdRes);
        cursorId = cmdRes.cursor.id;
        assert.neq(cursorId, NumberLong(0));

        const parallelShellFn =
            makeParallelShellFunctionString(cursorId, getMoreErrCodes, useSession, sessionId);
        getMoreJoiner = startParallelShell(parallelShellFn, st.s.port);

        // Wait until we know the mongod cursors are pinned.
        const curOpFilter = {"command.comment": kCommandCommentString};
        waitForCurOpByFailPoint(shard0DB, coll.getFullName(), kFailPointName, curOpFilter);
        waitForCurOpByFailPoint(shard1DB, coll.getFullName(), kFailPointName, curOpFilter);

        // Use the function provided by the caller to kill the sharded query.
        killFunc(cursorId);

        // The getMore should finish now that we've killed the cursor (even though the failpoint
        // is still enabled).
        getMoreJoiner();
        getMoreJoiner = null;

        // By now, the getMore run against the mongos has returned with an indication that the
        // cursor has been killed.  Verify that the cursor is really gone by running a
        // killCursors command, and checking that the cursor is reported as "not found".
        let killRes = mongosDB.runCommand({killCursors: coll.getName(), cursors: [cursorId]});
        assert.commandWorked(killRes);
        assert.eq(killRes.cursorsAlive, []);
        assert.eq(killRes.cursorsNotFound, [cursorId]);
        assert.eq(killRes.cursorsUnknown, []);

        // Eventually the cursors on the mongods should also be cleaned up. They should be
        // killed by mongos when the mongos cursor gets killed.
        function logActiveOpsAndIdleCursors(shardDB) {
            return () => "assert.soon failed: " +
                tojson(shardDB.getSiblingDB("admin")
                           .aggregate([{$currentOp: {idleCursors: true}}])
                           .toArray());
        }
        assert.soon(() => shard0DB.getSiblingDB("admin")
                              .aggregate([{$currentOp: {idleCursors: true}}, {$match: curOpFilter}])
                              .itcount() == 0,
                    logActiveOpsAndIdleCursors(shard0DB));
        assert.soon(() => shard1DB.getSiblingDB("admin")
                              .aggregate([{$currentOp: {idleCursors: true}}, {$match: curOpFilter}])
                              .itcount() == 0,
                    logActiveOpsAndIdleCursors(shard1DB));
    } finally {
        assert.commandWorked(
            shard0DB.adminCommand({configureFailPoint: kFailPointName, mode: "off"}));
        assert.commandWorked(
            shard1DB.adminCommand({configureFailPoint: kFailPointName, mode: "off"}));
        if (getMoreJoiner) {
            getMoreJoiner();
        }
    }
}

for (let useSession of [true, false]) {
    // Test that running 'killCursors' against a pinned mongos cursor (with pinned mongod
    // cursors) correctly cleans up all of the involved cursors.
    testShardedKillPinned({
        killFunc: function(mongosCursorId) {
            // Run killCursors against the mongos cursor. Verify that the cursor is reported as
            // killed successfully, and does not hang or return a "CursorInUse" error.
            let cmdRes =
                mongosDB.runCommand({killCursors: coll.getName(), cursors: [mongosCursorId]});
            assert.commandWorked(cmdRes);
            assert.eq(cmdRes.cursorsKilled, [mongosCursorId]);
            assert.eq(cmdRes.cursorsAlive, []);
            assert.eq(cmdRes.cursorsNotFound, []);
            assert.eq(cmdRes.cursorsUnknown, []);
        },
        getMoreErrCodes: ErrorCodes.CursorKilled,
        useSession: useSession
    });

    // Test that running killOp against one of the cursors pinned on mongod causes all involved
    // cursors to be killed.
    testShardedKillPinned({
        // This function ignores the mongos cursor id, since it instead uses currentOp to
        // obtain an op id to kill.
        killFunc: function() {
            let currentGetMoresArray = shard0DB.getSiblingDB("admin")
                                           .aggregate([
                                               {$currentOp: {}},
                                               {
                                                   $match: {
                                                       "command.getMore": {$exists: true},
                                                       "command.comment": kCommandCommentString
                                                   }
                                               }
                                           ])
                                           .toArray();
            assert.eq(1, currentGetMoresArray.length, currentGetMoresArray);
            let currentGetMore = currentGetMoresArray[0];
            let killOpResult = shard0DB.killOp(currentGetMore.opid);
            assert.commandWorked(killOpResult);
        },
        getMoreErrCodes: ErrorCodes.Interrupted,
        useSession: useSession
    });

    // Test that running killCursors against one of the cursors pinned on mongod causes all
    // involved cursors to be killed.
    testShardedKillPinned({
        // This function ignores the mongos cursor id, since it instead uses currentOp to
        // obtain the cursor id of one of the shard cursors.
        killFunc: function() {
            let currentGetMoresArray = shard0DB.getSiblingDB("admin")
                                           .aggregate([
                                               {$currentOp: {}},
                                               {
                                                   $match: {
                                                       "command.getMore": {$exists: true},
                                                       "command.comment": kCommandCommentString
                                                   }
                                               }
                                           ])
                                           .toArray();
            assert.eq(1, currentGetMoresArray.length, currentGetMoresArray);
            let currentGetMore = currentGetMoresArray[0];
            let shardCursorId = currentGetMore.command.getMore;
            let cmdRes =
                shard0DB.runCommand({killCursors: coll.getName(), cursors: [shardCursorId]});
            assert.commandWorked(cmdRes);
            assert.eq(cmdRes.cursorsKilled, [shardCursorId]);
            assert.eq(cmdRes.cursorsAlive, []);
            assert.eq(cmdRes.cursorsNotFound, []);
            assert.eq(cmdRes.cursorsUnknown, []);
        },
        getMoreErrCodes: ErrorCodes.CursorKilled,
        useSession: useSession
    });
}

// Test that running killSessions on the session which is running the getMore causes the
// cursor to be killed.
testShardedKillPinned({
    // This function ignores the mongos cursor id, since it instead uses listLocalSessions
    // to obtain the session id of the session running the getMore.
    killFunc: function() {
        // Must sort by 'lastUse' because there may be sessions left over on the server from
        // the previous runs. We will only call killSessions on the most recently used one.
        const localSessions = mongosDB
                                  .aggregate([
                                      {$listLocalSessions: {allUsers: true}},
                                      {$sort: {"lastUse": -1}},
                                  ])
                                  .toArray();

        const sessionUUID = localSessions[0]._id.id;
        assert.commandWorked(mongosDB.runCommand({killSessions: [{id: sessionUUID}]}));
    },
    // Killing a session on mongos kills all matching remote cursors (through KillCursors) then
    // all matching local operations (through KillOp), so the getMore can fail with either
    // CursorKilled or Interrupted depending on which response is returned first.
    getMoreErrCodes: [ErrorCodes.CursorKilled, ErrorCodes.Interrupted],
    useSession: true,
});

st.stop();
})();