Allow to change storage_policy to not less rich one

dbms/src/Storages/MergeTree/MergeTreeData.cpp

@@ -682,6 +682,57 @@ void MergeTreeData::setTTLExpressions(const ColumnsDescription::ColumnTTLs & new
 }
 
 
+void MergeTreeData::setStoragePolicy(const String & new_storage_policy_name, bool only_check)
+{
+    const auto old_storage_policy = getStoragePolicy();
+    const auto & new_storage_policy = global_context.getStoragePolicySelector()[new_storage_policy_name];
+
+    std::unordered_set<String> new_volume_names;
+    for (const auto & volume : new_storage_policy->getVolumes())
+        new_volume_names.insert(volume->getName());
+
+    for (const auto & volume : old_storage_policy->getVolumes())
+    {
+        if (new_volume_names.count(volume->getName()) == 0)
+            throw Exception("New storage policy shall contain volumes of old one", ErrorCodes::LOGICAL_ERROR);
+
+        std::unordered_set<String> new_disk_names;
+        for (const auto & disk : new_storage_policy->getVolumeByName(volume->getName())->disks)
+            new_disk_names.insert(disk->getName());
+
+        for (const auto & disk : volume->disks)
+            if (new_disk_names.count(disk->getName()) == 0)
+                throw Exception("New storage policy shall contain disks of old one", ErrorCodes::LOGICAL_ERROR);
+    }
+
+    std::unordered_set<String> all_diff_disk_names;
+    for (const auto & disk : new_storage_policy->getDisks())
+        all_diff_disk_names.insert(disk->getName());
+    for (const auto & disk : old_storage_policy->getDisks())
+        all_diff_disk_names.erase(disk->getName());
+
+    for (const String & disk_name : all_diff_disk_names)
+    {
+        const auto & path = getFullPathOnDisk(new_storage_policy->getDiskByName(disk_name));
+        if (Poco::File(path).exists())
+            throw Exception("New storage policy contain disks which already contain data of a table with the same name", ErrorCodes::LOGICAL_ERROR);
+    }
+
+    if (!only_check)
+    {
+        for (const String & disk_name : all_diff_disk_names)
+        {
+            const auto & path = getFullPathOnDisk(new_storage_policy->getDiskByName(disk_name));
+            Poco::File(path).createDirectories();
+            Poco::File(path + "detached").createDirectory();
+        }
+
+        storage_policy = new_storage_policy;
+        /// TODO: Query lock is fine but what about background moves??? And downloading of parts?
+    }
+}
+
+
 void MergeTreeData::MergingParams::check(const NamesAndTypesList & columns) const
 {
     if (!sign_column.empty() && mode != MergingParams::Collapsing && mode != MergingParams::VersionedCollapsing)
@@ -1479,6 +1530,9 @@ void MergeTreeData::checkAlterIsPossible(const AlterCommands & commands, const S
                 throw Exception{"Setting '" + changed_setting.name + "' is readonly for storage '" + getName() + "'",
                                  ErrorCodes::READONLY_SETTING};
             }
+
+            if (changed_setting.name == "storage_policy")
+                setStoragePolicy(changed_setting.value.safeGet<String>(), /* only_check = */ true);
         }
     }
 
@@ -1815,6 +1869,10 @@ void MergeTreeData::changeSettings(
         copy.applyChanges(new_changes);
         storage_settings.set(std::make_unique<const MergeTreeSettings>(copy));
         settings_ast = new_settings;
+
+        for (const auto & change : new_changes)
+            if (change.name == "storage_policy")
+                setStoragePolicy(change.value.safeGet<String>());
     }
 }
 

dbms/src/Storages/MergeTree/MergeTreeData.h

@@ -899,6 +899,8 @@ class MergeTreeData : public IStorage
     void setTTLExpressions(const ColumnsDescription::ColumnTTLs & new_column_ttls,
                            const ASTPtr & new_ttl_table_ast, bool only_check = false);
 
+    void setStoragePolicy(const String & new_storage_policy_name, bool only_check = false);
+
     /// Expression for column type conversion.
     /// If no conversions are needed, out_expression=nullptr.
     /// out_rename_map maps column files for the out_expression onto new table files.

dbms/src/Storages/MergeTree/MergeTreeSettings.h

@@ -105,7 +105,7 @@ struct MergeTreeSettings : public SettingsCollection<MergeTreeSettings>
     /// We check settings after storage creation
     static bool isReadonlySetting(const String & name)
     {
-        return name == "index_granularity" || name == "index_granularity_bytes" || name == "storage_policy";
+        return name == "index_granularity" || name == "index_granularity_bytes";
     }
 };
 

dbms/tests/integration/test_multiple_disks/configs/config.d/storage_configuration.xml

@@ -30,6 +30,17 @@
             </volumes>
         </small_jbod_with_external>
 
+        <one_more_small_jbod_with_external>
+            <volumes>
+                <m>
+                    <disk>jbod1</disk>
+                </m>
+                <e>
+                    <disk>external</disk>
+                </e>
+            </volumes>
+        </one_more_small_jbod_with_external>
+
         <!-- store on JBOD by default (round-robin), store big parts on external -->
         <jbods_with_external>
             <volumes>

dbms/tests/integration/test_multiple_disks/test.py

@@ -84,6 +84,22 @@ def test_system_tables(start_cluster):
             "max_data_part_size": "0",
             "move_factor": 0.1,
         },
+        {
+            "policy_name": "one_more_small_jbod_with_external",
+            "volume_name": "m",
+            "volume_priority": "1",
+            "disks": ["jbod1"],
+            "max_data_part_size": "0",
+            "move_factor": 0.1,
+        },
+        {
+            "policy_name": "one_more_small_jbod_with_external",
+            "volume_name": "e",
+            "volume_priority": "2",
+            "disks": ["external"],
+            "max_data_part_size": "0",
+            "move_factor": 0.1,
+        },
         {
             "policy_name": "jbods_with_external",
             "volume_name": "main",
@@ -223,6 +239,40 @@ def test_query_parser(start_cluster):
         node1.query("DROP TABLE IF EXISTS table_with_normal_policy")
 
 
+@pytest.mark.parametrize("name,engine", [
+    ("test_alter_policy","MergeTree()"),
+    ("replicated_test_alter_policy","ReplicatedMergeTree('/clickhouse/test_alter_policy', '1')",),
+])
+def test_alter_policy(start_cluster, name, engine):
+    try:
+        node1.query("""
+            CREATE TABLE {name} (
+                d UInt64
+            ) ENGINE = {engine}
+            ORDER BY d
+            SETTINGS storage_policy='small_jbod_with_external'
+        """.format(name=name, engine=engine))
+
+        assert node1.query("""SELECT storage_policy FROM system.tables WHERE name = '{name}'""".format(name=name)) == "small_jbod_with_external\n"
+
+        with pytest.raises(QueryRuntimeException):
+            node1.query("""ALTER TABLE {name} MODIFY SETTING storage_policy='one_more_small_jbod_with_external'""".format(name=name))
+
+        assert node1.query("""SELECT storage_policy FROM system.tables WHERE name = '{name}'""".format(name=name)) == "small_jbod_with_external\n"
+
+        node1.query("""ALTER TABLE {name} MODIFY SETTING storage_policy='jbods_with_external'""".format(name=name))
+
+        assert node1.query("""SELECT storage_policy FROM system.tables WHERE name = '{name}'""".format(name=name)) == "jbods_with_external\n"
+
+        with pytest.raises(QueryRuntimeException):
+            node1.query("""ALTER TABLE {name} MODIFY SETTING storage_policy='small_jbod_with_external'""".format(name=name))
+
+        assert node1.query("""SELECT storage_policy FROM system.tables WHERE name = '{name}'""".format(name=name)) == "jbods_with_external\n"
+
+    finally:
+        node1.query("DROP TABLE IF EXISTS {name}".format(name=name))
+
+
 def get_random_string(length):
     return ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(length))