Support specifying settings for Distributed engine in config (like for MergeTree)

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>

programs/server/config.xml

@@ -1401,6 +1401,13 @@
     </replicated_merge_tree>
     -->
 
+    <!-- Settings to fine tune Distributed tables. See documentation in source code, in DistributedSettings.h -->
+    <!--
+    <distributed>
+        <flush_on_detach>false</flush_on_detach>
+    </distributed>
+    -->
+
     <!-- Protection from accidental DROP.
          If size of a MergeTree table is greater than max_table_size_to_drop (in bytes) than table could not be dropped with any DROP query.
          If you want do delete one table and don't want to change clickhouse-server config, you could create special file <clickhouse-path>/flags/force_drop_table and make DROP once.

src/Interpreters/Context.cpp

@@ -29,6 +29,7 @@
 #include <Storages/MergeTree/ReplicatedFetchList.h>
 #include <Storages/MergeTree/MergeTreeData.h>
 #include <Storages/MergeTree/MergeTreeSettings.h>
+#include <Storages/Distributed/DistributedSettings.h>
 #include <Storages/CompressionCodecSelector.h>
 #include <Storages/StorageS3Settings.h>
 #include <Disks/DiskLocal.h>
@@ -111,6 +112,7 @@
 #include <Parsers/FunctionParameterValuesVisitor.h>
 #include <Parsers/ASTSelectWithUnionQuery.h>
 #include <Interpreters/InterpreterSelectWithUnionQuery.h>
+#include <base/defines.h>
 
 
 namespace fs = std::filesystem;
@@ -352,6 +354,7 @@ struct ContextSharedPart : boost::noncopyable
 
     std::optional<MergeTreeSettings> merge_tree_settings TSA_GUARDED_BY(mutex);   /// Settings of MergeTree* engines.
     std::optional<MergeTreeSettings> replicated_merge_tree_settings TSA_GUARDED_BY(mutex);   /// Settings of ReplicatedMergeTree* engines.
+    std::optional<DistributedSettings> distributed_settings TSA_GUARDED_BY(mutex);
     std::atomic_size_t max_table_size_to_drop = 50000000000lu; /// Protects MergeTree tables from accidental DROP (50GB by default)
     std::atomic_size_t max_partition_size_to_drop = 50000000000lu; /// Protects MergeTree partitions from accidental DROP (50GB by default)
     /// No lock required for format_schema_path modified only during initialization
@@ -4092,6 +4095,21 @@ const MergeTreeSettings & Context::getReplicatedMergeTreeSettings() const
     return *shared->replicated_merge_tree_settings;
 }
 
+const DistributedSettings & Context::getDistributedSettings() const
+{
+    std::lock_guard lock(shared->mutex);
+
+    if (!shared->distributed_settings)
+    {
+        const auto & config = shared->getConfigRefWithLock(lock);
+        DistributedSettings distributed_settings;
+        distributed_settings.loadFromConfig("distributed", config);
+        shared->distributed_settings.emplace(distributed_settings);
+    }
+
+    return *shared->distributed_settings;
+}
+
 const StorageS3Settings & Context::getStorageS3Settings() const
 {
     std::lock_guard lock(shared->mutex);

src/Interpreters/Context.h

@@ -113,6 +113,7 @@ class BlobStorageLog;
 class IAsynchronousReader;
 class IOUringReader;
 struct MergeTreeSettings;
+struct DistributedSettings;
 struct InitialAllRangesAnnouncement;
 struct ParallelReadRequest;
 struct ParallelReadResponse;
@@ -1073,6 +1074,7 @@ public:
 
     const MergeTreeSettings & getMergeTreeSettings() const;
     const MergeTreeSettings & getReplicatedMergeTreeSettings() const;
+    const DistributedSettings & getDistributedSettings() const;
     const StorageS3Settings & getStorageS3Settings() const;
 
     /// Prevents DROP TABLE if its size is greater than max_size (50GB by default, max_size=0 turn off this check)

src/Storages/Distributed/DistributedSettings.cpp

@@ -15,6 +15,27 @@ namespace ErrorCodes
 
 IMPLEMENT_SETTINGS_TRAITS(DistributedSettingsTraits, LIST_OF_DISTRIBUTED_SETTINGS)
 
+void DistributedSettings::loadFromConfig(const String & config_elem, const Poco::Util::AbstractConfiguration & config)
+{
+    if (!config.has(config_elem))
+        return;
+
+    Poco::Util::AbstractConfiguration::Keys config_keys;
+    config.keys(config_elem, config_keys);
+
+    try
+    {
+        for (const String & key : config_keys)
+            set(key, config.getString(config_elem + "." + key));
+    }
+    catch (Exception & e)
+    {
+        if (e.code() == ErrorCodes::UNKNOWN_SETTING)
+            e.addMessage("in Distributed config");
+        throw;
+    }
+}
+
 void DistributedSettings::loadFromQuery(ASTStorage & storage_def)
 {
     if (storage_def.settings)

src/Storages/Distributed/DistributedSettings.h

@@ -37,6 +37,7 @@ DECLARE_SETTINGS_TRAITS(DistributedSettingsTraits, LIST_OF_DISTRIBUTED_SETTINGS)
   */
 struct DistributedSettings : public BaseSettings<DistributedSettingsTraits>
 {
+    void loadFromConfig(const String & config_elem, const Poco::Util::AbstractConfiguration & config);
     void loadFromQuery(ASTStorage & storage_def);
 };
 

src/Storages/StorageDistributed.cpp

@@ -1922,7 +1922,7 @@ void registerStorageDistributed(StorageFactory & factory)
         }
 
         /// TODO: move some arguments from the arguments to the SETTINGS.
-        DistributedSettings distributed_settings;
+        DistributedSettings distributed_settings = context->getDistributedSettings();
         if (args.storage_def->settings)
         {
             distributed_settings.loadFromQuery(*args.storage_def);

tests/integration/test_distributed_config/configs/overrides.xml

@@ -0,0 +1,5 @@
+<clickhouse>
+    <distributed>
+        <flush_on_detach>0</flush_on_detach>
+    </distributed>
+</clickhouse>

tests/integration/test_distributed_config/test.py

@@ -0,0 +1,49 @@
+import pytest
+from helpers.cluster import ClickHouseCluster
+import logging
+
+cluster = ClickHouseCluster(__file__)
+node = cluster.add_instance("node", main_configs=["configs/overrides.xml"])
+
+
+@pytest.fixture(scope="module")
+def start_cluster():
+    try:
+        logging.info("Starting cluster...")
+        cluster.start()
+        logging.info("Cluster started")
+
+        yield cluster
+    finally:
+        cluster.shutdown()
+
+
+def test_distibuted_settings(start_cluster):
+    node.query("")
+    node.query(
+        """
+        CREATE TABLE data_1 (key Int) ENGINE Memory();
+        CREATE TABLE dist_1 as data_1 ENGINE Distributed(default, default, data_1) SETTINGS flush_on_detach = true;
+        SYSTEM STOP DISTRIBUTED SENDS dist_1;
+        INSERT INTO dist_1 SETTINGS prefer_localhost_replica=0 VALUES (1);
+        DETACH TABLE dist_1;
+    """
+    )
+    assert "flush_on_detach = 1" in node.query("SHOW CREATE dist_1")
+    # flush_on_detach=true, so data_1 should have 1 row
+    assert int(node.query("SELECT count() FROM data_1")) == 1
+
+    node.query(
+        """
+        CREATE TABLE data_2 (key Int) ENGINE Memory();
+        CREATE TABLE dist_2 as data_2 ENGINE Distributed(default, default, data_2);
+        SYSTEM STOP DISTRIBUTED SENDS dist_2;
+        INSERT INTO dist_2 SETTINGS prefer_localhost_replica=0 VALUES (2);
+        DETACH TABLE dist_2;
+    """
+    )
+    ## Settings are not added to CREATE (only specific one, like index_granularity for MergeTree)
+    # assert "flush_on_detach = 0" in node.query("SHOW CREATE dist_2")
+
+    # But settins are applied (flush_on_detach=false in config, so data_2 should not have any rows)
+    assert int(node.query("SELECT count() FROM data_2")) == 0