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225 lines
8.3 KiB
C++
225 lines
8.3 KiB
C++
#pragma once
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#include <DB/Storages/StorageDistributed.h>
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#include <DB/Parsers/formatAST.h>
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#include <DB/IO/WriteBufferFromFile.h>
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#include <DB/IO/CompressedWriteBuffer.h>
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#include <DB/DataStreams/NativeBlockOutputStream.h>
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#include <DB/Interpreters/InterpreterInsertQuery.h>
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#include <DB/Interpreters/Cluster.h>
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#include <DB/Common/Increment.h>
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#include <memory>
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#include <common/Revision.h>
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#include <iostream>
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#include <type_traits>
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namespace DB
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{
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/** Запись асинхронная - данные сначала записываются на локальную файловую систему, а потом отправляются на удалённые серверы.
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* Если Distributed таблица использует более одного шарда, то для того, чтобы поддерживалась запись,
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* при создании таблицы должен быть указан дополнительный параметр у ENGINE - ключ шардирования.
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* Ключ шардирования - произвольное выражение от столбцов. Например, rand() или UserID.
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* При записи блок данных разбивается по остатку от деления ключа шардирования на суммарный вес шардов,
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* и полученные блоки пишутся в сжатом Native формате в отдельные директории для отправки.
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* Для каждого адреса назначения (каждой директории с данными для отправки), в StorageDistributed создаётся отдельный поток,
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* который следит за директорией и отправляет данные. */
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class DistributedBlockOutputStream : public IBlockOutputStream
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{
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public:
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DistributedBlockOutputStream(StorageDistributed & storage, const ASTPtr & query_ast)
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: storage(storage), query_ast(query_ast)
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{
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}
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void write(const Block & block) override
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{
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if (storage.getShardingKeyExpr() && (storage.cluster.getShardsInfo().size() > 1))
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return writeSplit(block);
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writeImpl(block);
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}
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private:
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template <typename T>
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static std::vector<IColumn::Filter> createFiltersImpl(const size_t num_rows, const IColumn * column, const Cluster & cluster)
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{
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const auto total_weight = cluster.slot_to_shard.size();
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const auto num_shards = cluster.getShardsInfo().size();
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std::vector<IColumn::Filter> filters(num_shards);
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/** Деление отрицательного числа с остатком на положительное, в C++ даёт отрицательный остаток.
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* Для данной задачи это не подходит. Поэтому, будем обрабатывать знаковые типы как беззнаковые.
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* Это даёт уже что-то совсем не похожее на деление с остатком, но подходящее для данной задачи.
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*/
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using UnsignedT = typename std::make_unsigned<T>::type;
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/// const columns contain only one value, therefore we do not need to read it at every iteration
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if (column->isConst())
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{
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const auto data = typeid_cast<const ColumnConst<T> *>(column)->getData();
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const auto shard_num = cluster.slot_to_shard[static_cast<UnsignedT>(data) % total_weight];
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for (size_t i = 0; i < num_shards; ++i)
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filters[i].assign(num_rows, static_cast<UInt8>(shard_num == i));
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}
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else
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{
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const auto & data = typeid_cast<const ColumnVector<T> *>(column)->getData();
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for (size_t i = 0; i < num_shards; ++i)
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{
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filters[i].resize(num_rows);
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for (size_t j = 0; j < num_rows; ++j)
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filters[i][j] = cluster.slot_to_shard[static_cast<UnsignedT>(data[j]) % total_weight] == i;
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}
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}
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return filters;
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}
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std::vector<IColumn::Filter> createFilters(Block block)
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{
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using create_filters_sig = std::vector<IColumn::Filter>(size_t, const IColumn *, const Cluster &);
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/// hashmap of pointers to functions corresponding to each integral type
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static std::unordered_map<std::string, create_filters_sig *> creators{
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{ TypeName<UInt8>::get(), &createFiltersImpl<UInt8> },
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{ TypeName<UInt16>::get(), &createFiltersImpl<UInt16> },
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{ TypeName<UInt32>::get(), &createFiltersImpl<UInt32> },
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{ TypeName<UInt64>::get(), &createFiltersImpl<UInt64> },
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{ TypeName<Int8>::get(), &createFiltersImpl<Int8> },
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{ TypeName<Int16>::get(), &createFiltersImpl<Int16> },
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{ TypeName<Int32>::get(), &createFiltersImpl<Int32> },
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{ TypeName<Int64>::get(), &createFiltersImpl<Int64> },
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};
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storage.getShardingKeyExpr()->execute(block);
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const auto & key_column = block.getByName(storage.getShardingKeyColumnName());
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/// check that key column has valid type
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const auto it = creators.find(key_column.type->getName());
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return it != std::end(creators)
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? (*it->second)(block.rowsInFirstColumn(), key_column.column.get(), storage.cluster)
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: throw Exception{
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"Sharding key expression does not evaluate to an integer type",
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ErrorCodes::TYPE_MISMATCH
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};
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}
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void writeSplit(const Block & block)
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{
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const auto num_cols = block.columns();
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/// cache column pointers for later reuse
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std::vector<const IColumn*> columns(num_cols);
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for (size_t i = 0; i < columns.size(); ++i)
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columns[i] = block.getByPosition(i).column;
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auto filters = createFilters(block);
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const auto num_shards = storage.cluster.getShardsInfo().size();
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ssize_t size_hint = ((block.rowsInFirstColumn() + num_shards - 1) / num_shards) * 1.1; /// Число 1.1 выбрано наугад.
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for (size_t i = 0; i < num_shards; ++i)
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{
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auto target_block = block.cloneEmpty();
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for (size_t col = 0; col < num_cols; ++col)
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target_block.getByPosition(col).column = columns[col]->filter(filters[i], size_hint);
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if (target_block.rowsInFirstColumn())
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writeImpl(target_block, i);
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}
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}
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void writeImpl(const Block & block, const size_t shard_id = 0)
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{
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const auto & shard_info = storage.cluster.getShardsInfo()[shard_id];
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if (shard_info.getLocalNodeCount() > 0)
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writeToLocal(block, shard_info.getLocalNodeCount());
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/// dir_names is empty if shard has only local addresses
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if (!shard_info.dir_names.empty())
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writeToShard(block, shard_info.dir_names);
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}
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void writeToLocal(const Block & block, const size_t repeats)
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{
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InterpreterInsertQuery interp{query_ast, storage.context};
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auto block_io = interp.execute();
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block_io.out->writePrefix();
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for (size_t i = 0; i < repeats; ++i)
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block_io.out->write(block);
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block_io.out->writeSuffix();
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}
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void writeToShard(const Block & block, const std::vector<std::string> & dir_names)
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{
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/** tmp directory is used to ensure atomicity of transactions
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* and keep monitor thread out from reading incomplete data
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*/
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std::string first_file_tmp_path{};
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auto first = true;
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const auto & query_string = queryToString(query_ast);
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/// write first file, hardlink the others
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for (const auto & dir_name : dir_names)
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{
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const auto & path = storage.getPath() + dir_name + '/';
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/// ensure shard subdirectory creation and notify storage
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if (Poco::File(path).createDirectory())
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storage.requireDirectoryMonitor(dir_name);
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const auto & file_name = toString(Increment{path + "increment.txt"}.get(true)) + ".bin";
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const auto & block_file_path = path + file_name;
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/** on first iteration write block to a temporary directory for subsequent hardlinking to ensure
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* the inode is not freed until we're done */
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if (first)
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{
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first = false;
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const auto & tmp_path = path + "tmp/";
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Poco::File(tmp_path).createDirectory();
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const auto & block_file_tmp_path = tmp_path + file_name;
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first_file_tmp_path = block_file_tmp_path;
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WriteBufferFromFile out{block_file_tmp_path};
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CompressedWriteBuffer compress{out};
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NativeBlockOutputStream stream{compress, Revision::get()};
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writeStringBinary(query_string, out);
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stream.writePrefix();
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stream.write(block);
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stream.writeSuffix();
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}
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if (link(first_file_tmp_path.data(), block_file_path.data()))
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throwFromErrno("Could not link " + block_file_path + " to " + first_file_tmp_path);
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}
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/** remove the temporary file, enabling the OS to reclaim inode after all threads
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* have removed their corresponding files */
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Poco::File(first_file_tmp_path).remove();
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}
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StorageDistributed & storage;
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ASTPtr query_ast;
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};
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}
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