scylladb/test/cqlpy/test_lwt.py

# Copyright 2020-present ScyllaDB
#
# SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0

#############################################################################
# Various tests for Light-Weight Transactions (LWT) support in Scylla.
# Note that we have many more LWT tests in the cql-repl framework:
# ../cql/lwt*_test.cql, ../cql/cassandra_cql_test.cql.
#############################################################################

import re
import pytest
from cassandra.protocol import InvalidRequest

from .util import new_test_table, unique_key_int

@pytest.fixture(scope="module")
# FIXME: LWT is not supported with tablets yet. See #18066
def table1(cql, test_keyspace_vnodes):
    schema='p int, c int, r int, s int static, PRIMARY KEY(p, c)'
    with new_test_table(cql, test_keyspace_vnodes, schema) as table:
        yield table

# An LWT UPDATE whose condition uses non-static columns begins by reading
# the clustering row which must be specified by the WHERE. If there is a
# static column in the partition, it is read as well. The value of the all
# these columns - regular and static - is then passed to the condition.
# As discovered in issue #10081, if the row determined by WHERE does NOT
# exist, Scylla still needs to read the static column, but forgets to do so.
# this test reproduces this issue.
def test_lwt_missing_row_with_static(cql, table1):
    p = unique_key_int()
    # Insert into partition p just the static column - and no clustering rows.
    cql.execute(f'INSERT INTO {table1}(p, s) values ({p}, 1)')
    # Now, do an update with WHERE p={p} AND c=1. This clustering row does
    # *not* exist, so we expect to see r=null - and s=1 from before.
    r = list(cql.execute(f'UPDATE {table1} SET s=2,r=1 WHERE p={p} AND c=1 IF s=1 and r=null'))
    assert len(r) == 1
    assert r[0].applied == True
    # At this point we should have one row, for c=1 
    assert list(cql.execute(f'SELECT * FROM {table1} WHERE p={p}')) == [(p, 1, 2, 1)]

# The fact that to reproduce #10081 above we needed the condition (IF) to
# mention a non-static column as well, suggests that Scylla has a different code
# path for the case that the condition has *only* static columns. In fact,
# in that case, the WHERE doesn't even need to specify the clustering key -
# the partition key should be enough. The following test confirms that this
# is indeed the case.
def test_lwt_static_condition(cql, table1):
    p = unique_key_int()
    cql.execute(f'INSERT INTO {table1}(p, s) values ({p}, 1)')
    # When the condition only mentions static (partition-wide) columns,
    # it is allowed not to specify the clustering key in the WHERE:
    r = list(cql.execute(f'UPDATE {table1} SET s=2 WHERE p={p} IF s=1'))
    assert len(r) == 1
    assert r[0].applied == True
    assert list(cql.execute(f'SELECT * FROM {table1} WHERE p={p}')) == [(p, None, 2, None)]
    # When the condition also mentions a non-static column, WHERE must point
    # to a clustering column, i.e., mention the clustering key. If the
    # clustering key is missing, we get an InvalidRequest error, where the
    # message is slightly different between Scylla and Cassandra ("Missing
    # mandatory PRIMARY KEY part c" and "Some clustering keys are missing: c",
    # respectively.
    with pytest.raises(InvalidRequest, match=re.compile('missing', re.IGNORECASE)):
        cql.execute(f'UPDATE {table1} SET s=2 WHERE p={p} IF r=1')

# Generate an LWT update where there is no value for the partition key,
# as the WHERE restricts it using `p = {p} AND p = {p+1}`.
# Such queries are rejected.
def test_lwt_empty_partition_range(cql, table1):
    with pytest.raises(InvalidRequest):
        cql.execute(f"UPDATE {table1} SET r = 9000 WHERE p = 1 AND p = 1000 AND c = 2 IF r = 3")

# Generate an LWT update where there is no value for the clustering key,
# as the WHERE restricts it using `c = 2 AND c = 3`.
# Such queries are rejected.
def test_lwt_empty_clustering_range(cql, table1):
    with pytest.raises(InvalidRequest):
        cql.execute(f"UPDATE {table1} SET r = 9000 WHERE p = 1  AND c = 2 AND c = 2000 IF r = 3")

# In an LWT batch, if one of the condition fails the entire batch is not
# applied. All conditions in a batch use the same values before the batch,
# so if a batch has both a IF EXISTS and IF NOT EXISTS on the same row, they
# can't possibly both be true, so this batch is guaranteed to fail
# regardless of the data. Cassandra detects this specific conflict, and
# prints an error instead of silently failing the batch, but in ScyllaDB
# we considered this check to be inconsistent and unhelpful, and
# decided not to implement it, and this case is treated as a normal batch
# failure (not all conditions are true), not an error. See discussion in #13011.
# The test is marked scylla_only because it will fail on Cassandra which will
# report an error, not a batch failure.
def test_lwt_with_batch_conflict_1(cql, table1, scylla_only):
    p = unique_key_int()
    rs = cql.execute(f'BEGIN BATCH DELETE FROM {table1} WHERE p={p} AND c=1 IF EXISTS; INSERT INTO {table1}(p,c,r) VALUES ({p},1,2) IF NOT EXISTS; APPLY BATCH;')
    # Cassandra fails with: "Cannot mix IF EXISTS and IF NOT EXISTS conditions for the same row"
    for r in rs:
        assert r.applied == False

# However, Cassandra does not detect every case of a conflict between
# different conditions in a batch. For example, trying both "IF r=1"
# and "IF r=2" returns a not-applied - not an error message.
def test_lwt_with_batch_conflict_2(cql, table1):
    p = unique_key_int()
    rs = list(cql.execute(f'BEGIN BATCH UPDATE {table1} SET r=10 WHERE p={p} AND c=1 IF r=1; UPDATE {table1} SET r=20 WHERE p={p} AND c=1 IF r=2;  APPLY BATCH;'))
    # Note that as a documented difference between Scylla and Cassandra,
    # Cassandra returns just one applied=False in the result r, while
    # Scylla returns a separate row for each of the two conditions.
    for r in rs:
        assert r.applied == False

# Moreover, there are cases where Cassandra prevents mixing
# IF EXISTS with different conditions such as IF r=1, despite
# the fact that the conditions are not contradictory.
def test_lwt_with_batch_conflict_3(cql, table1, scylla_only):
    p = unique_key_int()
    cql.execute(f'INSERT INTO {table1}(p,c,r) VALUES ({p},1,1)')
    rs = cql.execute(f'BEGIN BATCH UPDATE {table1} SET r=10 WHERE p={p} AND c=1 IF r=1; UPDATE {table1} SET r=20 WHERE p={p} AND c=1 IF EXISTS;  APPLY BATCH;')
    # Cassandra fails with: "Cannot mix IF conditions and IF EXISTS for the same row"
    for r in rs:
        assert r.applied == True

# During a static column update, the clustering key is not required in the WHERE clause.
# A batch composed of a query that updates a static column and a query that inserts
# a new row is allowed and will be applied successfully.
def test_lwt_with_batch_conflict_4(cql, table1):
    p = unique_key_int()
    cql.execute(f'INSERT INTO {table1}(p,c,r,s) VALUES ({p},1,1,1)')
    rs = cql.execute(f'BEGIN BATCH UPDATE {table1} SET s=NULL WHERE p={p} IF EXISTS; INSERT INTO {table1}(p,c,r) VALUES ({p},2,2) IF NOT EXISTS; APPLY BATCH;')
    for r in rs:
        assert r.applied == True

# However, even for static columns, mixing IF EXISTS and other conditions
# is disallowed in Cassandra.
def test_lwt_with_batch_conflict_5(cql, table1, scylla_only):
    p = unique_key_int()
    cql.execute(f'INSERT INTO {table1}(p,c,r,s) VALUES ({p},1,1,1)')
    rs = cql.execute(f'BEGIN BATCH UPDATE {table1} SET s=NULL WHERE p={p} IF EXISTS; UPDATE {table1} SET s=NULL WHERE p={p} IF s = 1; APPLY BATCH;')
    # Cassandra fails with: "Cannot mix IF conditions and IF NOT EXISTS for the same row"
    # The fact that "IF NOT EXISTS" is used in the error message is a bit misleading,
    # but that's what Cassandra returns
    for r in rs:
        assert r.applied == True


# Test NOT IN condition in LWT IF clause
#
# Cassandra rejects this with "line 1:84 no viable alternative at input 'NOT' (...AND c=1 IF r [NOT]...)"",
# indicating its grammar only supports this for WHERE, not IF.
def test_lwt_not_in(cql, table1, cassandra_bug):
    p = unique_key_int()
    cql.execute(f'INSERT INTO {table1}(p, c, r) values ({p}, 1, 1)')
    rs = list(cql.execute(f'UPDATE {table1} SET r=2 WHERE p={p} AND c=1 IF r NOT IN (1, 2)'))
    for r in rs:
        assert r.applied == False
    # Check that we look at the entire list, not just the first element
    rs = list(cql.execute(f'UPDATE {table1} SET r=2 WHERE p={p} AND c=1 IF r NOT IN (2, 1)'))
    for r in rs:
        assert r.applied == False
    rs = list(cql.execute(f'UPDATE {table1} SET r=2 WHERE p={p} AND c=1 IF r NOT IN (7, 8)'))
    for r in rs:
        assert r.applied == True
    # LWT IF conditions don't treat NULL as a special value
    rs = list(cql.execute(f'UPDATE {table1} SET r=NULL WHERE p={p} AND c=1 IF r NOT IN (NULL, 7, 8)'))
    for r in rs:
        assert r.applied == True
    # Similar, but now show that NULL input fails the condition
    rs = list(cql.execute(f'UPDATE {table1} SET r=NULL WHERE p={p} AND c=1 IF r NOT IN (NULL, 7, 8)'))
    for r in rs:
        assert r.applied == False