add setting to define filename pattern for part exports

docs/en/engines/table-engines/mergetree-family/part_export.md

@@ -84,6 +84,13 @@ In case a table function is used as the destination, the schema can be omitted a
 - **Default**: `true`
 - **Description**: If set to true, throws if pending patch parts exists for a given part. Note that by default mutations are applied to all parts, which means that if a mutation in practice would only affetct part/partition x, all the other parts/partition will throw upon export. The exception is when the `IN PARTITION` clause was used in the mutation command. Note the `IN PARTITION` clause is not properly implemented for plain MergeTree tables.
 
+### export_merge_tree_part_filename_pattern
+
+- **Type**: `String`
+- **Default**: `{part_name}_{checksum}`
+- **Description**: Pattern for the filename of the exported merge tree part. The `part_name` and `checksum` are calculated and replaced on the fly. Additional macros are supported.
+
+
 ## Examples
 
 ### Basic Export to S3

docs/en/engines/table-engines/mergetree-family/partition_export.md

@@ -82,6 +82,12 @@ TO TABLE [destination_database.]destination_table
 - **Default**: `true`
 - **Description**: If set to true, throws if pending patch parts exists for a given part. Note that by default mutations are applied to all parts, which means that if a mutation in practice would only affetct part/partition x, all the other parts/partition will throw upon export. The exception is when the `IN PARTITION` clause was used in the mutation command. Note the `IN PARTITION` clause is not properly implemented for plain MergeTree tables.
 
+### export_merge_tree_part_filename_pattern
+
+- **Type**: `String`
+- **Default**: `{part_name}_{checksum}`
+- **Description**: Pattern for the filename of the exported merge tree part. The `part_name` and `checksum` are calculated and replaced on the fly. Additional macros are supported.
+
 ## Examples
 
 ### Basic Export to S3

src/Core/Settings.cpp

@@ -7388,6 +7388,9 @@ Possible values:
 - `` (empty value) - use server or session timezone
 
 Default value is empty.
+)", 0) \
+    DECLARE(String, export_merge_tree_part_filename_pattern, "{part_name}_{checksum}", R"(
+Pattern for the filename of the exported merge tree part. The `part_name` and `checksum` are calculated and replaced on the fly. Additional macros are supported.
 )", 0) \
     \
     /* ####################################################### */ \

src/Storages/ExportReplicatedMergeTreePartitionManifest.h

@@ -116,6 +116,7 @@ struct ExportReplicatedMergeTreePartitionManifest
     size_t max_bytes_per_file;
     size_t max_rows_per_file;
     MergeTreePartExportManifest::FileAlreadyExistsPolicy file_already_exists_policy;
+    String filename_pattern;
     bool lock_inside_the_task; /// todo temporary
 
     std::string toJsonString() const
@@ -139,6 +140,7 @@ struct ExportReplicatedMergeTreePartitionManifest
         json.set("max_bytes_per_file", max_bytes_per_file);
         json.set("max_rows_per_file", max_rows_per_file);
         json.set("file_already_exists_policy", String(magic_enum::enum_name(file_already_exists_policy)));
+        json.set("filename_pattern", filename_pattern);
         json.set("create_time", create_time);
         json.set("max_retries", max_retries);
         json.set("ttl_seconds", ttl_seconds);
@@ -175,6 +177,7 @@ struct ExportReplicatedMergeTreePartitionManifest
         manifest.parquet_parallel_encoding = json->getValue<bool>("parquet_parallel_encoding");
         manifest.max_bytes_per_file = json->getValue<size_t>("max_bytes_per_file");
         manifest.max_rows_per_file = json->getValue<size_t>("max_rows_per_file");
+        manifest.filename_pattern = json->getValue<String>("filename_pattern");
 
         if (json->has("file_already_exists_policy"))
         {

src/Storages/MergeTree/ExportPartTask.cpp

@@ -3,11 +3,13 @@
 #include <Storages/MergeTree/MergeTreeSequentialSource.h>
 #include <Storages/MergeTree/MergeTreeData.h>
 #include <Interpreters/Context.h>
-#include <Interpreters/DatabaseCatalog.h>
 #include <Interpreters/inplaceBlockConversions.h>
 #include <Core/Settings.h>
+#include <Common/Macros.h>
+#include <boost/algorithm/string/replace.hpp>
 #include <Interpreters/ExpressionActions.h>
 #include <Interpreters/ActionsDAG.h>
+#include <Interpreters/DatabaseCatalog.h>
 #include <Processors/Executors/CompletedPipelineExecutor.h>
 #include <Processors/QueryPlan/BuildQueryPipelineSettings.h>
 #include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>
@@ -47,6 +49,7 @@ namespace Setting
     extern const SettingsUInt64 export_merge_tree_part_max_bytes_per_file;
     extern const SettingsUInt64 export_merge_tree_part_max_rows_per_file;
     extern const SettingsBool allow_experimental_analyzer;
+    extern const SettingsString export_merge_tree_part_filename_pattern;
 }
 
 namespace
@@ -93,6 +96,23 @@ namespace
             plan_for_part.addStep(std::move(expression_step));
         }
     }
+
+    String buildDestinationFilename(
+        const MergeTreePartExportManifest & manifest,
+        const StorageID & storage_id,
+        const ContextPtr & local_context)
+    {
+        auto filename = manifest.settings[Setting::export_merge_tree_part_filename_pattern].value;
+
+        boost::replace_all(filename, "{part_name}", manifest.data_part->name);
+        boost::replace_all(filename, "{checksum}", manifest.data_part->checksums.getTotalChecksumHex());
+
+        Macros::MacroExpansionInfo macro_info;
+        macro_info.table_id = storage_id;
+        filename = local_context->getMacros()->expand(filename, macro_info);
+
+        return filename;
+    }
 }
 
 ExportPartTask::ExportPartTask(MergeTreeData & storage_, const MergeTreePartExportManifest & manifest_)
@@ -154,8 +174,10 @@ bool ExportPartTask::executeStep()
 
     try
     {
+        const auto filename = buildDestinationFilename(manifest, storage.getStorageID(), local_context);
+
         sink = destination_storage->import(
-            manifest.data_part->name + "_" + manifest.data_part->checksums.getTotalChecksumHex(),
+            filename,
             block_with_partition_values,
             new_file_path_callback,
             manifest.file_already_exists_policy == MergeTreePartExportManifest::FileAlreadyExistsPolicy::overwrite,

src/Storages/MergeTree/ExportPartitionTaskScheduler.cpp

@@ -56,7 +56,9 @@ namespace
         context_copy->setSetting("export_merge_tree_part_throw_on_pending_mutations", false);
         context_copy->setSetting("export_merge_tree_part_throw_on_pending_patch_parts", false);
 
-        return context_copy;
+        context_copy->setSetting("export_merge_tree_part_filename_pattern", manifest.filename_pattern);
+
+	return context_copy;
     }
 }
 

src/Storages/StorageReplicatedMergeTree.cpp

@@ -217,6 +217,7 @@ namespace Setting
     extern const SettingsBool export_merge_tree_part_throw_on_pending_mutations;
     extern const SettingsBool export_merge_tree_part_throw_on_pending_patch_parts;
     extern const SettingsBool export_merge_tree_partition_lock_inside_the_task;
+    extern const SettingsString export_merge_tree_part_filename_pattern;
 }
 
 namespace MergeTreeSetting
@@ -8209,6 +8210,7 @@ void StorageReplicatedMergeTree::exportPartitionToTable(const PartitionCommand &
 
 
     manifest.file_already_exists_policy = query_context->getSettingsRef()[Setting::export_merge_tree_part_file_already_exists_policy].value;
+    manifest.filename_pattern = query_context->getSettingsRef()[Setting::export_merge_tree_part_filename_pattern].value;
 
     ops.emplace_back(zkutil::makeCreateRequest(
         fs::path(partition_exports_path) / "metadata.json", 

tests/integration/test_export_replicated_mt_partition_to_object_storage/configs/macros_shard1_replica1.xml

@@ -0,0 +1,6 @@
+<clickhouse>
+    <macros>
+        <shard>shard1</shard>
+        <replica>replica1</replica>
+    </macros>
+</clickhouse>

tests/integration/test_export_replicated_mt_partition_to_object_storage/configs/macros_shard2_replica1.xml

@@ -0,0 +1,6 @@
+<clickhouse>
+    <macros>
+        <shard>shard2</shard>
+        <replica>replica1</replica>
+    </macros>
+</clickhouse>

tests/integration/test_export_replicated_mt_partition_to_object_storage/test.py

@@ -118,6 +118,26 @@ def cluster():
             with_zookeeper=True,
             keeper_required_feature_flags=["multi_read"],
         )
+        # Sharded instances for filename pattern tests
+        cluster.add_instance(
+            "shard1_replica1",
+            main_configs=["configs/named_collections.xml", "configs/allow_experimental_export_partition.xml", "configs/macros_shard1_replica1.xml"],
+            user_configs=["configs/users.d/profile.xml"],
+            with_minio=True,
+            stay_alive=True,
+            with_zookeeper=True,
+            keeper_required_feature_flags=["multi_read"],
+        )
+
+        cluster.add_instance(
+            "shard2_replica1",
+            main_configs=["configs/named_collections.xml", "configs/allow_experimental_export_partition.xml", "configs/macros_shard2_replica1.xml"],
+            user_configs=["configs/users.d/profile.xml"],
+            with_minio=True,
+            stay_alive=True,
+            with_zookeeper=True,
+            keeper_required_feature_flags=["multi_read"],
+        )
         logging.info("Starting cluster...")
         cluster.start()
         yield cluster
@@ -161,6 +181,14 @@ def create_tables_and_insert_data(node, mt_table, s3_table, replica_name):
     create_s3_table(node, s3_table)
 
 
+def create_sharded_tables_and_insert_data(node, mt_table, s3_table, replica_name):
+    """Create sharded ReplicatedMergeTree table with {shard} macro in ZooKeeper path."""
+    node.query(f"CREATE TABLE {mt_table} (id UInt64, year UInt16) ENGINE = ReplicatedMergeTree('/clickhouse/tables/{{shard}}/{mt_table}', '{replica_name}') PARTITION BY year ORDER BY tuple()")
+    node.query(f"INSERT INTO {mt_table} VALUES (1, 2020), (2, 2020), (3, 2020), (4, 2021)")
+
+    create_s3_table(node, s3_table)
+
+
 def test_restart_nodes_during_export(cluster):
     skip_if_remote_database_disk_enabled(cluster)
     node = cluster.instances["replica1"]
@@ -1148,3 +1176,82 @@ def test_export_partition_with_mixed_computed_columns(cluster):
             AND partition_id = '1'
     """)
     assert status.strip() == "COMPLETED", f"Expected COMPLETED status, got: {status}"
+
+
+def test_sharded_export_partition_with_filename_pattern(cluster):
+    """Test that export partition with filename pattern prevents collisions in sharded setup."""
+    shard1_r1 = cluster.instances["shard1_replica1"]
+    shard2_r1 = cluster.instances["shard2_replica1"]
+    watcher_node = cluster.instances["watcher_node"]
+
+    mt_table = "sharded_mt_table"
+    s3_table = "sharded_s3_table"
+
+    # Create sharded tables on all shards with same partition data (same part names)
+    # Each shard uses different ZooKeeper path via {shard} macro
+    create_sharded_tables_and_insert_data(shard1_r1, mt_table, s3_table, "replica1")
+    create_sharded_tables_and_insert_data(shard2_r1, mt_table, s3_table, "replica1")
+    create_s3_table(watcher_node, s3_table)
+
+    # Export partition from both shards with filename pattern including shard
+    # This should prevent filename collisions
+    shard1_r1.query(
+        f"ALTER TABLE {mt_table} EXPORT PARTITION ID '2020' TO TABLE {s3_table} "
+        f"SETTINGS export_merge_tree_part_filename_pattern = '{{part_name}}_{{shard}}_{{replica}}_{{checksum}}'"
+    )
+    shard2_r1.query(
+        f"ALTER TABLE {mt_table} EXPORT PARTITION ID '2020' TO TABLE {s3_table} "
+        f"SETTINGS export_merge_tree_part_filename_pattern = '{{part_name}}_{{shard}}_{{replica}}_{{checksum}}'"
+    )
+
+    # Wait for exports to complete
+    wait_for_export_status(shard1_r1, mt_table, s3_table, "2020", "COMPLETED")
+    wait_for_export_status(shard2_r1, mt_table, s3_table, "2020", "COMPLETED")
+
+    total_count = watcher_node.query(f"SELECT count() FROM {s3_table} WHERE year = 2020").strip()
+    assert total_count == "6", f"Expected 6 total rows (3 from each shard), got {total_count}"
+
+    # Verify filenames contain shard information (check via S3 directly)
+    # Get all files from S3 - query from watcher_node since S3 is shared
+    files_shard1 = watcher_node.query(
+        f"SELECT _file FROM s3(s3_conn, filename='{s3_table}/**', format='One') WHERE _file LIKE '%shard1%' LIMIT 1"
+    ).strip()
+    files_shard2 = watcher_node.query(
+        f"SELECT _file FROM s3(s3_conn, filename='{s3_table}/**', format='One') WHERE _file LIKE '%shard2%' LIMIT 1"
+    ).strip()
+
+    # Both shards should have files with their shard names
+    assert "shard1" in files_shard1 or files_shard1 == "", f"Expected shard1 in filenames, got: {files_shard1}"
+    assert "shard2" in files_shard2 or files_shard2 == "", f"Expected shard2 in filenames, got: {files_shard2}"
+
+
+def test_sharded_export_partition_default_pattern(cluster):
+    shard1_r1 = cluster.instances["shard1_replica1"]
+    shard2_r1 = cluster.instances["shard2_replica1"]
+    watcher_node = cluster.instances["watcher_node"]
+
+    mt_table = "sharded_mt_table_default"
+    s3_table = "sharded_s3_table_default"
+
+    # Create sharded tables with different ZooKeeper paths per shard
+    create_sharded_tables_and_insert_data(shard1_r1, mt_table, s3_table, "replica1")
+    create_sharded_tables_and_insert_data(shard2_r1, mt_table, s3_table, "replica1")
+    create_s3_table(watcher_node, s3_table)
+
+    # Export with default pattern ({part_name}_{checksum}) - may cause collisions if parts have same name and the same checksum
+    shard1_r1.query(
+        f"ALTER TABLE {mt_table} EXPORT PARTITION ID '2020' TO TABLE {s3_table}"
+    )
+    shard2_r1.query(
+        f"ALTER TABLE {mt_table} EXPORT PARTITION ID '2020' TO TABLE {s3_table}"
+    )
+
+    wait_for_export_status(shard1_r1, mt_table, s3_table, "2020", "COMPLETED")
+    wait_for_export_status(shard2_r1, mt_table, s3_table, "2020", "COMPLETED")
+
+    # Both exports should complete (even if there are collisions, the overwrite policy handles it)
+    # S3 tables are shared, so query from watcher_node
+    total_count = watcher_node.query(f"SELECT count() FROM {s3_table} WHERE year = 2020").strip()
+
+    # only one file with 3 rows should be present
+    assert int(total_count) == 3, f"Expected 3 rows, got {total_count}"

tests/queries/0_stateless/03608_export_merge_tree_part_filename_pattern.reference

@@ -0,0 +1,16 @@
+---- Test: Default pattern {part_name}_{checksum}
+1	2020
+2	2020
+3	2020
+---- Verify filename matches 2020_1_1_0_*.1.parquet
+1
+---- Test: Custom prefix pattern
+4	2021
+---- Verify filename matches myprefix_2021_2_2_0.1.parquet
+1
+---- Test: Pattern with macros
+1	2020
+2	2020
+3	2020
+---- Verify macros expanded (no literal braces in parquet filenames, that's the best we can do for stateless tests)
+1

tests/queries/0_stateless/03608_export_merge_tree_part_filename_pattern.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Tags: no-fasttest
+# Tag no-fasttest: requires s3 storage
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+R=$RANDOM
+mt="mt_${R}"
+dest1="fp_dest1_${R}"
+dest2="fp_dest2_${R}"
+dest3="fp_dest3_${R}"
+
+query() {
+    $CLICKHOUSE_CLIENT --query "$1"
+}
+
+query "DROP TABLE IF EXISTS $mt, $dest1, $dest2, $dest3"
+
+query "CREATE TABLE $mt (id UInt64, year UInt16) ENGINE = MergeTree() PARTITION BY year ORDER BY tuple()"
+query "INSERT INTO $mt VALUES (1, 2020), (2, 2020), (3, 2020), (4, 2021)"
+
+query "CREATE TABLE $dest1 (id UInt64, year UInt16) ENGINE = S3(s3_conn, filename='$dest1', format=Parquet, partition_strategy='hive') PARTITION BY year"
+query "CREATE TABLE $dest2 (id UInt64, year UInt16) ENGINE = S3(s3_conn, filename='$dest2', format=Parquet, partition_strategy='hive') PARTITION BY year"
+query "CREATE TABLE $dest3 (id UInt64, year UInt16) ENGINE = S3(s3_conn, filename='$dest3', format=Parquet, partition_strategy='hive') PARTITION BY year"
+
+echo "---- Test: Default pattern {part_name}_{checksum}"
+query "ALTER TABLE $mt EXPORT PART '2020_1_1_0' TO TABLE $dest1 SETTINGS allow_experimental_export_merge_tree_part = 1, export_merge_tree_part_filename_pattern = '{part_name}_{checksum}'"
+sleep 3
+query "SELECT * FROM $dest1 ORDER BY id"
+echo "---- Verify filename matches 2020_1_1_0_*.1.parquet"
+query "SELECT count() FROM s3(s3_conn, filename='$dest1/**/2020_1_1_0_*.1.parquet', format='One')"
+
+echo "---- Test: Custom prefix pattern"
+query "ALTER TABLE $mt EXPORT PART '2021_2_2_0' TO TABLE $dest2 SETTINGS allow_experimental_export_merge_tree_part = 1, export_merge_tree_part_filename_pattern = 'myprefix_{part_name}'"
+sleep 3
+query "SELECT * FROM $dest2 ORDER BY id"
+echo "---- Verify filename matches myprefix_2021_2_2_0.1.parquet"
+query "SELECT count() FROM s3(s3_conn, filename='$dest2/**/myprefix_2021_2_2_0.1.parquet', format='One')"
+
+echo "---- Test: Pattern with macros"
+query "ALTER TABLE $mt EXPORT PART '2020_1_1_0' TO TABLE $dest3 SETTINGS allow_experimental_export_merge_tree_part = 1, export_merge_tree_part_filename_pattern = '{database}_{table}_{part_name}'"
+sleep 3
+query "SELECT * FROM $dest3 ORDER BY id"
+echo "---- Verify macros expanded (no literal braces in parquet filenames, that's the best we can do for stateless tests)"
+query "SELECT count() = 0 FROM s3(s3_conn, filename='$dest3/**/*.1.parquet', format='One') WHERE _file LIKE '%{%'"
+
+query "DROP TABLE IF EXISTS $mt, $dest1, $dest2, $dest3"