If you have really wide table with many thousands of columns and you want to drop / modify column.
For wide parts it working fine, but for compact clickhouse would try to allocate a lot of memory and going to be killed via OOM killer.



**Does it reproduce on recent release?**

Yes, 21.9

**How to reproduce**
```
clickhouse-client -mn --query="SELECT 'CREATE TABLE xxx_really_wide( ' || arrayStringConcat(groupArray('column_'|| toString(number) || ' Nullable(UInt32)'), ',') || ') ENGINE=MergeTree ORDER BY assumeNotNull(column_0)' FROM numbers(6000) FORMAT TSVRaw" | clickhouse-client -mn

clickhouse-client -mn --query="SELECT arrayStringConcat(replicate('1', range(6000)), ',') FROM numbers(300) FORMAT TSVRaw" | clickhouse-client -mn --query "INSERT INTO xxx_really_wide FORMAT CSV " --send_logs_level='trace'
```

```
SELECT *
FROM system.merges
FORMAT Vertical

Query id: d9751847-a689-49f0-aab3-f868d9c08e34

Row 1:
──────
database:                    default
table:                       xxx_really_wide
elapsed:                     84.8952157
progress:                    0
num_parts:                   1
source_part_names:           ['all_1_1_0']
result_part_name:            all_1_1_0_3
source_part_paths:           ['/var/lib/clickhouse/data/default/xxx_really_wide/all_1_1_0/']
result_part_path:            /var/lib/clickhouse/data/default/xxx_really_wide/all_1_1_0_3/
partition_id:                all
is_mutation:                 1
total_size_bytes_compressed: 456027
total_size_marks:            2
bytes_read_uncompressed:     0
rows_read:                   0
bytes_written_uncompressed:  0
rows_written:                0
columns_written:             0
memory_usage:                16836533272
thread_id:                   16171
merge_type:
merge_algorithm:

Row 2:
──────
database:                    default
table:                       xxx_really_wide
elapsed:                     84.8947852
progress:                    0
num_parts:                   1
source_part_names:           ['all_2_2_0']
result_part_name:            all_2_2_0_3
source_part_paths:           ['/var/lib/clickhouse/data/default/xxx_really_wide/all_2_2_0/']
result_part_path:            /var/lib/clickhouse/data/default/xxx_really_wide/all_2_2_0_3/
partition_id:                all
is_mutation:                 1
total_size_bytes_compressed: 468027
total_size_marks:            2
bytes_read_uncompressed:     0
rows_read:                   0
bytes_written_uncompressed:  0
rows_written:                0
columns_written:             0
memory_usage:                16706294896
thread_id:                   16174
merge_type:
merge_algorithm:
```

return std::make_shared<MaterializingTransform>(header);
    });
    return pipeline;
}
void MutationsInterpreter::validate()
{
    if (!select_interpreter)
        select_interpreter = std::make_unique<InterpreterSelectQuery>(mutation_ast, context, storage, metadata_snapshot, select_limits);
    const Settings & settings = context->getSettingsRef();
    
    
    if (startsWith(storage->getName(), "Replicated") && !settings.allow_nondeterministic_mutations)
    {
        for (const auto & command : commands)
        {
            const auto nondeterministic_func_data = findFirstNonDeterministicFunctionName(command, context);
            if (nondeterministic_func_data.subquery)
                throw Exception(ErrorCodes::BAD_ARGUMENTS, "ALTER UPDATE/ALTER DELETE statement with subquery may be nondeterministic, "
                                                           "see allow_nondeterministic_mutations setting");
            if (nondeterministic_func_data.nondeterministic_function_name)
                throw Exception(ErrorCodes::BAD_ARGUMENTS,
                    "ALTER UPDATE/ALTER DELETE statements must use only deterministic functions. "
                    "Function '{}' is non-deterministic", *nondeterministic_func_data.nondeterministic_function_name);
        }
    }
    QueryPlan plan;
    select_interpreter->buildQueryPlan(plan);
    auto pipeline = addStreamsForLaterStages(stages, plan);
}
QueryPipelineBuilder MutationsInterpreter::execute()