mongo/jstests/core/txns/transactions_write_conflicts.js

/**
 * Verify that transactions correctly abort for all possible types of write conflicts.
 *
 * BACKGROUND:
 *
 * Snapshot isolation guarantees that every transaction, conceptually, runs against its own,
 * consistent "snapshot" of the database, which reflects the effects of all previously committed
 * transactions. Every transaction performs its reads and writes against this snapshot, adjusting
 * for the effects of any writes executed inside the transaction. Snapshot isolation enforces a
 * policy for serializing writes between transactions known as the "First Updater Wins" rule.
 * Intuitively, this rule states that concurrent transactions are not allowed to write to the same
 * document. It enforces this via an optimistic concurrency control mechanism, as opposed to a
 * pessimistic one i.e. locking the document. If two concurrent transactions T1 and T2 write to the
 * same document, only the first writer will succeed. So, for example, if transaction T2 tries to
 * write to a document already written to by T1 this will cause T2's write to fail with a
 * "WriteConflict" error, and transaction T2 will be aborted.
 *
 * In MongoDB, a "write" by a transaction is any insert, update, or delete to a document. This means
 * that all of these operation types can produce write conflicts with each other as a result of
 * running in concurrent transactions. The test cases below illustrate the possible write conflict
 * types for both single and multi-document writes.
 *
 * Note that two transactions can be "concurrent" even if they don't necessarily execute on
 * different threads within the server. Transactions under snapshot isolation are defined to be
 * "concurrent" if their transactional lifetimes overlap. The lifetime of a transaction is the
 * interval [Start(T), Commit(T)], where Start(T) is the read timestamp of transaction (the
 * timestamp of the snapshot it executes against) and Commit(T) is the timestamp of the
 * transaction's commit operation. In the tests below, we use two separate sessions so we can
 * arbitrarily interleave operations between two different transactions, simulating the execution of
 * two "truly" concurrent transactions.
 *
 *  @tags: [
 *    uses_transactions,
 *  ]
 */
import {WriteConflictHelpers} from "jstests/core/txns/libs/write_conflicts.js";

const dbName = "test";
const collName = "transactions_write_conflicts";

const testDB = db.getSiblingDB(dbName);
const coll = testDB[collName];

// Clean up and create test collection.
testDB.runCommand({drop: collName, writeConcern: {w: "majority"}});
testDB.runCommand({create: coll.getName(), writeConcern: {w: "majority"}});

/***********************************************************************************************
 * Single document write conflicts.
 **********************************************************************************************/

jsTestLog("Test single document write conflicts.");

print("insert-insert conflict.");
let t1Op = {insert: collName, documents: [{_id: 1, t1: 1}]};
let t2Op = {insert: collName, documents: [{_id: 1, t2: 1}]};
let expectedDocs1 = [{_id: 1, t1: 1}];
WriteConflictHelpers.writeConflictTest(coll, t1Op, t2Op, expectedDocs1, WriteConflictHelpers.T1StartsFirstAndWins);
let expectedDocs2 = [{_id: 1, t2: 1}];
WriteConflictHelpers.writeConflictTest(coll, t1Op, t2Op, expectedDocs2, WriteConflictHelpers.T2StartsSecondAndWins);

print("update-update conflict");
let initOp = {insert: collName, documents: [{_id: 1}]}; // the document to update.
t1Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t1: 1}}}],
};
t2Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t2: 1}}}],
};
expectedDocs1 = [{_id: 1, t1: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1, t2: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("upsert-upsert conflict");
t1Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t1: 1}}, upsert: true}],
};
t2Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t2: 1}}, upsert: true}],
};
expectedDocs1 = [{_id: 1, t1: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1, t2: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("delete-delete conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}],
}; // the document to delete.
t1Op = {
    delete: collName,
    deletes: [{q: {_id: 1}, limit: 1}],
};
t2Op = {
    delete: collName,
    deletes: [{q: {_id: 1}, limit: 1}],
};
expectedDocs1 = [];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("update-delete conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}],
}; // the document to delete/update.
t1Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t1: 1}}}],
};
t2Op = {
    delete: collName,
    deletes: [{q: {_id: 1}, limit: 1}],
};
expectedDocs1 = [{_id: 1, t1: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("delete-update conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}],
}; // the document to delete/update.
t1Op = {
    delete: collName,
    deletes: [{q: {_id: 1}, limit: 1}],
};
t2Op = {
    update: collName,
    updates: [{q: {_id: 1}, u: {$set: {t2: 1}}}],
};
expectedDocs1 = [];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1, t2: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

/***********************************************************************************************
 * Multi-document and predicate based write conflicts.
 **********************************************************************************************/

jsTestLog("Test multi-document and predicate based write conflicts.");

print("batch insert-batch insert conflict");
t1Op = {
    insert: collName,
    documents: [{_id: 1}, {_id: 2}, {_id: 3}],
};
t2Op = {
    insert: collName,
    documents: [{_id: 2}, {_id: 3}, {_id: 4}],
};
expectedDocs1 = [{_id: 1}, {_id: 2}, {_id: 3}];
WriteConflictHelpers.writeConflictTest(coll, t1Op, t2Op, expectedDocs1, WriteConflictHelpers.T1StartsFirstAndWins);
expectedDocs2 = [{_id: 2}, {_id: 3}, {_id: 4}];
WriteConflictHelpers.writeConflictTest(coll, t1Op, t2Op, expectedDocs2, WriteConflictHelpers.T2StartsSecondAndWins);

print("multiupdate-multiupdate conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}, {_id: 2}, {_id: 3}, {_id: 4}], // the documents to update/delete.
};
// Predicate intersection: [{_id: 2}, {_id: 3}]
t1Op = {
    update: collName,
    updates: [{q: {_id: {$lte: 3}}, u: {$set: {t1: 1}}, multi: true}],
};
t2Op = {
    update: collName,
    updates: [{q: {_id: {$gte: 2}}, u: {$set: {t2: 1}}, multi: true}],
};
expectedDocs1 = [{_id: 1, t1: 1}, {_id: 2, t1: 1}, {_id: 3, t1: 1}, {_id: 4}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1}, {_id: 2, t2: 1}, {_id: 3, t2: 1}, {_id: 4, t2: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("multiupdate-multidelete conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}, {_id: 2}, {_id: 3}, {_id: 4}], // the documents to update/delete.
};
// Predicate intersection: [{_id: 2}, {_id: 3}]
t1Op = {
    update: collName,
    updates: [{q: {_id: {$lte: 3}}, u: {$set: {t1: 1}}, multi: true}],
};
t2Op = {
    delete: collName,
    deletes: [{q: {_id: {$gte: 2}}, limit: 0}],
};
expectedDocs1 = [{_id: 1, t1: 1}, {_id: 2, t1: 1}, {_id: 3, t1: 1}, {_id: 4}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("multidelete-multiupdate conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}, {_id: 2}, {_id: 3}, {_id: 4}], // the documents to update/delete.
};
// Predicate intersection: [{_id: 2}, {_id: 3}]
t1Op = {
    delete: collName,
    deletes: [{q: {_id: {$lte: 3}}, limit: 0}],
};
t2Op = {
    update: collName,
    updates: [{q: {_id: {$gte: 2}}, u: {$set: {t2: 1}}, multi: true}],
};
expectedDocs1 = [{_id: 4}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1}, {_id: 2, t2: 1}, {_id: 3, t2: 1}, {_id: 4, t2: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);

print("multidelete-multidelete conflict");
initOp = {
    insert: collName,
    documents: [{_id: 1}, {_id: 2}, {_id: 3}, {_id: 4}], // the documents to delete.
};
// Predicate intersection: [{_id: 2}, {_id: 3}]
t1Op = {
    delete: collName,
    deletes: [{q: {_id: {$lte: 3}}, limit: 0}],
};
t2Op = {
    delete: collName,
    deletes: [{q: {_id: {$gte: 2}}, limit: 0}],
};
expectedDocs1 = [{_id: 4}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs1,
    WriteConflictHelpers.T1StartsFirstAndWins,
    initOp,
);
expectedDocs2 = [{_id: 1}];
WriteConflictHelpers.writeConflictTest(
    coll,
    t1Op,
    t2Op,
    expectedDocs2,
    WriteConflictHelpers.T2StartsSecondAndWins,
    initOp,
);