[Draft] Export MergeTree part to Parquet

src/Interpreters/InterpreterAlterQuery.cpp

@@ -479,6 +479,11 @@ AccessRightsElements InterpreterAlterQuery::getRequiredAccessForCommand(const AS
             }
             break;
         }
+        case ASTAlterCommand::EXPORT_PART:
+        {
+            required_access.emplace_back(AccessType::ALTER_MOVE_PARTITION, database, table);
+            break;
+        }
         case ASTAlterCommand::REPLACE_PARTITION:
         {
             required_access.emplace_back(AccessType::SELECT, command.from_database, command.from_table);

src/Parsers/ASTAlterQuery.cpp

@@ -343,6 +343,12 @@ void ASTAlterCommand::formatImpl(WriteBuffer & ostr, const FormatSettings & sett
             ostr << quoteString(move_destination_name);
         }
     }
+    else if (type == ASTAlterCommand::EXPORT_PART)
+    {
+        ostr << (settings.hilite ? hilite_keyword : "") << "EXPORT " << (part ? "PART " : "PARTITION ")
+             << (settings.hilite ? hilite_none : "");
+        partition->formatImpl(ostr, settings, state, frame);
+    }
     else if (type == ASTAlterCommand::REPLACE_PARTITION)
     {
         ostr << (settings.hilite ? hilite_keyword : "") << (replace ? "REPLACE" : "ATTACH") << " PARTITION "

src/Parsers/ASTAlterQuery.h

@@ -71,6 +71,7 @@ class ASTAlterCommand : public IAST
         FREEZE_ALL,
         UNFREEZE_PARTITION,
         UNFREEZE_ALL,
+        EXPORT_PART,
 
         DELETE,
         UPDATE,

src/Parsers/CommonParsers.h

@@ -325,6 +325,7 @@ namespace DB
     MR_MACROS(MONTHS, "MONTHS") \
     MR_MACROS(MOVE_PART, "MOVE PART") \
     MR_MACROS(MOVE_PARTITION, "MOVE PARTITION") \
+    MR_MACROS(EXPORT_PART, "EXPORT PART") \
     MR_MACROS(MOVE, "MOVE") \
     MR_MACROS(MS, "MS") \
     MR_MACROS(MUTATION, "MUTATION") \

src/Parsers/ParserAlterQuery.cpp

@@ -82,6 +82,7 @@ bool ParserAlterCommand::parseImpl(Pos & pos, ASTPtr & node, Expected & expected
     ParserKeyword s_forget_partition(Keyword::FORGET_PARTITION);
     ParserKeyword s_move_partition(Keyword::MOVE_PARTITION);
     ParserKeyword s_move_part(Keyword::MOVE_PART);
+    ParserKeyword s_export_part(Keyword::EXPORT_PART);
     ParserKeyword s_drop_detached_partition(Keyword::DROP_DETACHED_PARTITION);
     ParserKeyword s_drop_detached_part(Keyword::DROP_DETACHED_PART);
     ParserKeyword s_fetch_partition(Keyword::FETCH_PARTITION);
@@ -554,6 +555,31 @@ bool ParserAlterCommand::parseImpl(Pos & pos, ASTPtr & node, Expected & expected
                     command->move_destination_name = ast_space_name->as<ASTLiteral &>().value.safeGet<const String &>();
                 }
             }
+            else if (s_export_part.ignore(pos, expected))
+            {
+                if (!parser_string_and_substituion.parse(pos, command_partition, expected))
+                    return false;
+
+                command->type = ASTAlterCommand::EXPORT_PART;
+                command->part = true;
+
+//                if (s_to_disk.ignore(pos, expected))
+//                    command->move_destination_type = DataDestinationType::DISK;
+//                else if (s_to_volume.ignore(pos, expected))
+//                    command->move_destination_type = DataDestinationType::VOLUME;
+//                else if (s_to_shard.ignore(pos, expected))
+//                {
+//                    command->move_destination_type = DataDestinationType::SHARD;
+//                }
+//                else
+//                    return false;
+//
+//                ASTPtr ast_space_name;
+//                if (!parser_string_literal.parse(pos, ast_space_name, expected))
+//                    return false;
+//
+//                command->move_destination_name = ast_space_name->as<ASTLiteral &>().value.safeGet<const String &>();
+            }
             else if (s_add_constraint.ignore(pos, expected))
             {
                 if (s_if_not_exists.ignore(pos, expected))

src/Storages/MergeTree/MergeTreeData.cpp

@@ -85,6 +85,7 @@
 #include <Storages/StorageReplicatedMergeTree.h>
 #include <Storages/VirtualColumnUtils.h>
 #include <Storages/MergeTree/MergeTreeIndexGranularityAdaptive.h>
+#include <Storages/MergeTree/exportMTPartToParquet.h>
 
 #include <boost/range/algorithm_ext/erase.hpp>
 #include <boost/algorithm/string/join.hpp>
@@ -5594,6 +5595,21 @@ Pipe MergeTreeData::alterPartition(
             }
             break;
 
+            case PartitionCommand::EXPORT_PART:
+            {
+                if (command.part)
+                {
+                    auto part_name = command.partition->as<ASTLiteral &>().value.safeGet<String>();
+                    auto data_part = getPartIfExists(part_name, {DataPartStates::value_type::Active});
+
+                    if (!data_part)
+                        throw Exception(ErrorCodes::NO_SUCH_DATA_PART, "No part {} in committed state", part_name);
+
+                    exportMTPartToParquet(*this, data_part, query_context);
+                }
+                break;
+            }
+
             case PartitionCommand::DROP_DETACHED_PARTITION:
                 dropDetached(command.partition, command.part, query_context);
                 break;

src/Storages/MergeTree/exportMTPartToParquet.cpp

@@ -0,0 +1,84 @@
+#include <Storages/MergeTree/exportMTPartToParquet.h>
+#include <Processors/QueryPlan/QueryPlan.h>
+#include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>
+#include <Storages/MergeTree/MergeTreeSequentialSource.h>
+#include <Processors/Formats/Impl/ParquetBlockOutputFormat.h>
+#include <QueryPipeline/QueryPipelineBuilder.h>
+#include <Processors/Executors/PullingPipelineExecutor.h>
+#include <Processors/Executors/PushingPipelineExecutor.h>
+#include <Formats/FormatFactory.h>
+
+
+namespace DB
+{
+
+void exportMTPartToParquet(const MergeTreeData & data, const MergeTreeData::DataPartPtr & data_part, ContextPtr context)
+{
+    auto metadata_snapshot = data.getInMemoryMetadataPtr();
+    Names columns_to_read = metadata_snapshot->getColumns().getNamesOfPhysical();
+    StorageSnapshotPtr storage_snapshot = data.getStorageSnapshot(metadata_snapshot, context);
+
+    MergeTreeData::IMutationsSnapshot::Params params
+    {
+        .metadata_version = metadata_snapshot->getMetadataVersion(),
+        .min_part_metadata_version = data_part->getMetadataVersion(),
+    };
+
+    auto mutations_snapshot = data.getMutationsSnapshot(params);
+
+    auto alter_conversions = MergeTreeData::getAlterConversionsForPart(
+        data_part,
+        mutations_snapshot,
+        metadata_snapshot,
+        context);
+
+    QueryPlan plan;
+
+    // todoa arthur
+    MergeTreeSequentialSourceType read_type = MergeTreeSequentialSourceType::Merge;
+
+    bool apply_deleted_mask = true;
+    bool read_with_direct_io = false;
+    bool prefetch = false;
+
+    createReadFromPartStep(
+        read_type,
+        plan,
+        data,
+        storage_snapshot,
+        data_part,
+        alter_conversions,
+        columns_to_read,
+        nullptr,
+        apply_deleted_mask,
+        std::nullopt,
+        read_with_direct_io,
+        prefetch,
+        context,
+        getLogger("abcde"));
+
+    auto pipeline_settings = BuildQueryPipelineSettings::fromContext(context);
+    auto optimization_settings = QueryPlanOptimizationSettings::fromContext(context);
+    auto builder = plan.buildQueryPipeline(optimization_settings, pipeline_settings);
+
+    QueryPipeline pipeline = QueryPipelineBuilder::getPipeline(std::move(*builder));
+    auto header_block = pipeline.getHeader();
+
+    auto out_file_name = data_part->name + ".parquet";
+
+    auto out_file = std::make_shared<WriteBufferFromFile>(out_file_name);
+    auto parquet_output = FormatFactory::instance().getOutputFormat("Parquet", *out_file, header_block, context);
+    PullingPipelineExecutor executor(pipeline);
+
+    Block block;
+    while (executor.pull(block))
+    {
+        parquet_output->write(block);
+    }
+
+    parquet_output->finalize();
+
+    out_file->finalize();
+}
+
+}

src/Storages/MergeTree/exportMTPartToParquet.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <Storages/MergeTree/MergeTreeData.h>
+
+namespace DB
+{
+
+void exportMTPartToParquet(const MergeTreeData & data, const MergeTreeData::DataPartPtr & data_part, ContextPtr context);
+
+}

src/Storages/PartitionCommands.cpp

@@ -51,6 +51,14 @@ std::optional<PartitionCommand> PartitionCommand::parse(const ASTAlterCommand *
         res.part = command_ast->part;
         return res;
     }
+    if (command_ast->type == ASTAlterCommand::EXPORT_PART)
+    {
+        PartitionCommand res;
+        res.type = EXPORT_PART;
+        res.partition = command_ast->partition->clone();
+        res.part = command_ast->part;
+        return res;
+    }
     if (command_ast->type == ASTAlterCommand::MOVE_PARTITION)
     {
         PartitionCommand res;

src/Storages/PartitionCommands.h

@@ -33,6 +33,7 @@ struct PartitionCommand
         UNFREEZE_ALL_PARTITIONS,
         UNFREEZE_PARTITION,
         REPLACE_PARTITION,
+        EXPORT_PART,
     };
 
     Type type = UNKNOWN;