scylladb/test/alternator/test_tablets.py

# Copyright 2024-present ScyllaDB
#
# SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0

# Tests for the Scylla-only "tablets" feature.
#
# Ideally, tablets are just an implementation detail (replacing the
# old vnodes), that the DynamoDB API user would not even be aware
# of. So there should be very few, if any, tests in this file.
# However, temporarily - while the tablets feature is only partially
# working, it is useful
# to have here a few tests that clarify the situation and how to
# override it. Most of these tests, or perhaps even this entire file,
# will probably go away eventually.

import pytest
import boto3
from botocore.exceptions import ClientError

from .util import new_test_table, wait_for_gsi, random_string, full_scan, full_query, multiset, scylla_config_read, scylla_config_temporary

# All tests in this file are scylla-only
@pytest.fixture(scope="function", autouse=True)
def all_tests_are_scylla_only(scylla_only):
    pass

# Utility function for checking if a given table is using tablets
# or not. We rely on some knowledge of Alternator internals:
# 1. For table with name X, Scylla creates a keyspace called alternator_X
# 2. We can read a CQL system table using the ".scylla.alternator." prefix.
def uses_tablets(dynamodb, table):
    info = dynamodb.Table('.scylla.alternator.system_schema.scylla_keyspaces')
    try:
        response = info.query(
            KeyConditions={'keyspace_name': {
                    'AttributeValueList': ['alternator_'+table.name],
                    'ComparisonOperator':  'EQ'}})
    except dynamodb.meta.client.exceptions.ResourceNotFoundException:
        # The internal Scylla table doesn't even exist, either this isn't
        # Scylla or it's older Scylla and doesn't use tablets.
        return False
    if not 'Items' in response or not response['Items']:
        return False
    if 'initial_tablets' in response['Items'][0] and response['Items'][0]['initial_tablets']:
        return True
    return False

# Utility function for checking whether using tablets by a given table
# is in-line with the global Scylla configuration flag regarding tablets.
def assert_tablets_usage_follows_config(dynamodb, table):
    tablets_default = scylla_config_read(dynamodb, 'tablets_mode_for_new_keyspaces')
    if tablets_default in ("\"enabled\"", "\"enforced\"", None):
        assert uses_tablets(dynamodb, table)
    else:
        assert not uses_tablets(dynamodb, table)

# New Alternator tables are created with tablets or vnodes, according to the
# "tablets_mode_for_new_keyspaces" configuration flag.
def test_default_tablets(dynamodb):
    schema = {
        'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
        'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]}
    with new_test_table(dynamodb, **schema) as table:
        assert_tablets_usage_follows_config(dynamodb, table)

# Tests for the initial_tablets tag named "system:initial_tablets".
# This tag was earlier called "experimental:initial_tablets".
# Ref. #26211
initial_tablets_tag = 'system:initial_tablets'

# Check that a table created with a number as initial_tablets will use 
# tablets. Different numbers have different meanings (0 asked to use
# default number, any other number overrides the default) but they
# all enable tablets.
def test_initial_tablets_int(dynamodb):
    for value in ['0', '4']:
        schema = {
            'Tags': [{'Key': initial_tablets_tag, 'Value': value}],
            'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
            'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]}
        with new_test_table(dynamodb, **schema) as table:
            assert uses_tablets(dynamodb, table)

# Check that a table created with a non-number (e.g., the string "none")
# as initial_tablets, will not use tablets.
def test_initial_tablets_not_int(dynamodb):
    schema = {
        'Tags': [{'Key': initial_tablets_tag, 'Value': 'none'}],
        'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
        'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]}
    with new_test_table(dynamodb, **schema) as table:
        assert not uses_tablets(dynamodb, table)

# Usage of tablets is determined by the configuration flag
# "tablets_mode_for_new_keyspaces", as well as by the per-table
# "system:initial_tablets" tag. The tag overrides the configuration,
# except when the configuration flag's value is "enforced" -
# then if the tag asks for vnodes, an error is generated.
def test_tablets_tag_vs_config(dynamodb):
    schema = {
        'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
        'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]
    }
    schema_tablets = {**schema, 'Tags': [{'Key': initial_tablets_tag, 'Value': '0'}]}
    schema_vnodes = {**schema, 'Tags': [{'Key': initial_tablets_tag, 'Value': 'none'}]}
    # With tablets_mode_for_new_keyspaces=enabled, tablets are used unless
    # the user explicitly asks for vnodes (schema_vnodes).
    with scylla_config_temporary(dynamodb, 'tablets_mode_for_new_keyspaces', 'enabled'):
        with new_test_table(dynamodb, **schema) as table:
            assert uses_tablets(dynamodb, table)
        with new_test_table(dynamodb, **schema_tablets) as table:
            assert uses_tablets(dynamodb, table)
        with new_test_table(dynamodb, **schema_vnodes) as table:
            assert not uses_tablets(dynamodb, table)
    # With tablets_mode_for_new_keyspaces=disabled, vnodes are used unless
    # the user explicitly asks tablets (schema_tablets)
    with scylla_config_temporary(dynamodb, 'tablets_mode_for_new_keyspaces', 'disabled'):
        with new_test_table(dynamodb, **schema) as table:
            assert not uses_tablets(dynamodb, table)
        with new_test_table(dynamodb, **schema_tablets) as table:
            assert uses_tablets(dynamodb, table)
        with new_test_table(dynamodb, **schema_vnodes) as table:
            assert not uses_tablets(dynamodb, table)
    # With tablets_mode_for_new_keyspaces=enforced, tablets are used except
    # when the user requests vnodes, which is a ValidationException.
    with scylla_config_temporary(dynamodb, 'tablets_mode_for_new_keyspaces', 'enforced'):
        with new_test_table(dynamodb, **schema) as table:
            assert uses_tablets(dynamodb, table)
        with new_test_table(dynamodb, **schema_tablets) as table:
            assert uses_tablets(dynamodb, table)
        with pytest.raises(ClientError, match='ValidationException.*tablets'):
            with new_test_table(dynamodb, **schema_vnodes) as table:
                pass

# Before Alternator Streams is supported with tablets (#23838), let's verify
# that enabling Streams results in an orderly error. This test should be
# deleted when #23838 is fixed.
def test_streams_enable_error_with_tablets(dynamodb):
    # Test attempting to create a table already with streams
    with pytest.raises(ClientError, match='ValidationException.*tablets'):
        with new_test_table(dynamodb,
            Tags=[{'Key': initial_tablets_tag, 'Value': '4'}],
            StreamSpecification={'StreamEnabled': True, 'StreamViewType': 'KEYS_ONLY'},
            KeySchema=[ { 'AttributeName': 'p', 'KeyType': 'HASH' }, ],
            AttributeDefinitions=[ { 'AttributeName': 'p', 'AttributeType': 'S' } ]) as table:
            pass
    # Test attempting to add a stream to an existing table
    with new_test_table(dynamodb,
        Tags=[{'Key': initial_tablets_tag, 'Value': '4'}],
        KeySchema=[ { 'AttributeName': 'p', 'KeyType': 'HASH' }, ],
        AttributeDefinitions=[ { 'AttributeName': 'p', 'AttributeType': 'S' } ]) as table:
        with pytest.raises(ClientError, match='ValidationException.*tablets'):
            table.update(StreamSpecification={'StreamEnabled': True, 'StreamViewType': 'KEYS_ONLY'});

# For a while (see #18068) it was possible to create an Alternator table with
# tablets enabled and choose LWT for write isolation (always_use_lwt)
# but the writes themselves failed. This test verifies that this is no longer
# the case, and the LWT writes succeed even when tablets are used.
def test_alternator_tablets_and_lwt(dynamodb):
    schema = {
        'Tags': [
            {'Key': initial_tablets_tag, 'Value': '0'},
            {'Key': 'system:write_isolation', 'Value': 'always_use_lwt'}],
        'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
        'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]}
    with new_test_table(dynamodb, **schema) as table:
        assert_tablets_usage_follows_config(dynamodb, table)
        # This put_item() failed before #18068 was fixed:
        table.put_item(Item={'p': 'hello'})
        assert table.get_item(Key={'p': 'hello'}, ConsistentRead=True)['Item'] == {'p': 'hello'}

# An Alternator table created with tablets and with a write isolation
# mode that doesn't use LWT ("forbid_rmw") works normally, even
# before #18068 is fixed.
def test_alternator_tablets_without_lwt(dynamodb):
    schema = {
        'Tags': [
            {'Key': initial_tablets_tag, 'Value': '0'},
            {'Key': 'system:write_isolation', 'Value': 'forbid_rmw'}],
        'KeySchema': [ { 'AttributeName': 'p', 'KeyType': 'HASH' } ],
        'AttributeDefinitions': [ { 'AttributeName': 'p', 'AttributeType': 'S' }]}
    with new_test_table(dynamodb, **schema) as table:
        assert_tablets_usage_follows_config(dynamodb, table)
        table.put_item(Item={'p': 'hello'})
        assert table.get_item(Key={'p': 'hello'})['Item'] == {'p': 'hello'}