ClickHouse/dbms/src/Storages/StorageBuffer.cpp

#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/InterpreterInsertQuery.h>
#include <Interpreters/InterpreterAlterQuery.h>
#include <DataStreams/IProfilingBlockInputStream.h>
#include <Databases/IDatabase.h>
#include <Storages/StorageBuffer.h>
#include <Parsers/ASTInsertQuery.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTExpressionList.h>
#include <Common/setThreadName.h>
#include <Common/CurrentMetrics.h>
#include <common/logger_useful.h>
#include <Poco/Ext/ThreadNumber.h>

#include <ext/range.hpp>


namespace ProfileEvents
{
    extern const Event StorageBufferFlush;
    extern const Event StorageBufferErrorOnFlush;
    extern const Event StorageBufferPassedAllMinThresholds;
    extern const Event StorageBufferPassedTimeMaxThreshold;
    extern const Event StorageBufferPassedRowsMaxThreshold;
    extern const Event StorageBufferPassedBytesMaxThreshold;
}

namespace CurrentMetrics
{
    extern const Metric StorageBufferRows;
    extern const Metric StorageBufferBytes;
}


namespace DB
{

namespace ErrorCodes
{
    extern const int INFINITE_LOOP;
    extern const int BLOCKS_HAS_DIFFERENT_STRUCTURE;
}


StoragePtr StorageBuffer::create(const std::string & name_, NamesAndTypesListPtr columns_,
    const NamesAndTypesList & materialized_columns_,
    const NamesAndTypesList & alias_columns_,
    const ColumnDefaults & column_defaults_,
    Context & context_,
    size_t num_shards_, const Thresholds & min_thresholds_, const Thresholds & max_thresholds_,
    const String & destination_database_, const String & destination_table_)
{
    return make_shared(
        name_, columns_, materialized_columns_, alias_columns_, column_defaults_,
        context_, num_shards_, min_thresholds_, max_thresholds_, destination_database_, destination_table_);
}


StorageBuffer::StorageBuffer(const std::string & name_, NamesAndTypesListPtr columns_,
    const NamesAndTypesList & materialized_columns_,
    const NamesAndTypesList & alias_columns_,
    const ColumnDefaults & column_defaults_,
    Context & context_,
    size_t num_shards_, const Thresholds & min_thresholds_, const Thresholds & max_thresholds_,
    const String & destination_database_, const String & destination_table_)
    : IStorage{materialized_columns_, alias_columns_, column_defaults_},
    name(name_), columns(columns_), context(context_),
    num_shards(num_shards_), buffers(num_shards_),
    min_thresholds(min_thresholds_), max_thresholds(max_thresholds_),
    destination_database(destination_database_), destination_table(destination_table_),
    no_destination(destination_database.empty() && destination_table.empty()),
    log(&Logger::get("StorageBuffer (" + name + ")")),
    flush_thread(&StorageBuffer::flushThread, this)
{
}


/// Reads from one buffer (from one block) under its mutex.
class BufferBlockInputStream : public IProfilingBlockInputStream
{
public:
    BufferBlockInputStream(const Names & column_names_, StorageBuffer::Buffer & buffer_)
        : column_names(column_names_.begin(), column_names_.end()), buffer(buffer_) {}

    String getName() const { return "Buffer"; }

    String getID() const
    {
        std::stringstream res;
        res << "Buffer(" << &buffer;

        for (const auto & name : column_names)
            res << ", " << name;

        res << ")";
        return res.str();
    }

protected:
    Block readImpl()
    {
        Block res;

        if (has_been_read)
            return res;
        has_been_read = true;

        std::lock_guard<std::mutex> lock(buffer.mutex);

        if (!buffer.data.rows())
            return res;

        for (const auto & name : column_names)
        {
            auto & col = buffer.data.getByName(name);
            res.insert(ColumnWithTypeAndName(col.column->clone(), col.type, name));
        }

        return res;
    }

private:
    NameSet column_names;
    StorageBuffer::Buffer & buffer;
    bool has_been_read = false;
};


BlockInputStreams StorageBuffer::read(
    const Names & column_names,
    ASTPtr query,
    const Context & context,
    const Settings & settings,
    QueryProcessingStage::Enum & processed_stage,
    size_t max_block_size,
    unsigned threads)
{
    processed_stage = QueryProcessingStage::FetchColumns;

    BlockInputStreams streams_from_dst;

    if (!no_destination)
    {
        auto destination = context.getTable(destination_database, destination_table);

        if (destination.get() == this)
            throw Exception("Destination table is myself. Read will cause infinite loop.", ErrorCodes::INFINITE_LOOP);

        /** Turn off the optimization "transfer to PREWHERE",
          *  since Buffer does not support PREWHERE.
          */
        Settings modified_settings = settings;
        modified_settings.optimize_move_to_prewhere = false;

        streams_from_dst = destination->read(column_names, query, context, modified_settings, processed_stage, max_block_size, threads);
    }

    BlockInputStreams streams_from_buffers;
    streams_from_buffers.reserve(num_shards);
    for (auto & buf : buffers)
        streams_from_buffers.push_back(std::make_shared<BufferBlockInputStream>(column_names, buf));

    /** If the sources from the table were processed before some non-initial stage of query execution,
      * then sources from the buffers must also be wrapped in the processing pipeline before the same stage.
      */
    if (processed_stage > QueryProcessingStage::FetchColumns)
        for (auto & stream : streams_from_buffers)
            stream = InterpreterSelectQuery(query, context, processed_stage, 0, stream).execute().in;

    streams_from_dst.insert(streams_from_dst.end(), streams_from_buffers.begin(), streams_from_buffers.end());
    return streams_from_dst;
}


static void appendBlock(const Block & from, Block & to)
{
    if (!to)
        throw Exception("Cannot append to empty block", ErrorCodes::LOGICAL_ERROR);

    from.checkNumberOfRows();
    to.checkNumberOfRows();

    size_t rows = from.rows();
    size_t bytes = from.bytes();

    CurrentMetrics::add(CurrentMetrics::StorageBufferRows, rows);
    CurrentMetrics::add(CurrentMetrics::StorageBufferBytes, bytes);

    size_t old_rows = to.rows();

    try
    {
        for (size_t column_no = 0, columns = to.columns(); column_no < columns; ++column_no)
        {
            const IColumn & col_from = *from.safeGetByPosition(column_no).column.get();
            IColumn & col_to = *to.safeGetByPosition(column_no).column.get();

            if (col_from.getName() != col_to.getName())
                throw Exception("Cannot append block to another: different type of columns at index " + toString(column_no)
                    + ". Block 1: " + from.dumpStructure() + ". Block 2: " + to.dumpStructure(), ErrorCodes::BLOCKS_HAS_DIFFERENT_STRUCTURE);

            col_to.insertRangeFrom(col_from, 0, rows);
        }
    }
    catch (...)
    {
        /// Rollback changes.
        try
        {
            /// Avoid "memory limit exceeded" exceptions during rollback.
            TemporarilyDisableMemoryTracker temporarily_disable_memory_tracker;

            for (size_t column_no = 0, columns = to.columns(); column_no < columns; ++column_no)
            {
                ColumnPtr & col_to = to.safeGetByPosition(column_no).column;
                if (col_to->size() != old_rows)
                    col_to = col_to->cut(0, old_rows);
            }
        }
        catch (...)
        {
            /// In case when we cannot rollback, do not leave incorrect state in memory.
            std::terminate();
        }

        throw;
    }
}


class BufferBlockOutputStream : public IBlockOutputStream
{
public:
    BufferBlockOutputStream(StorageBuffer & storage_) : storage(storage_) {}

    void write(const Block & block) override
    {
        if (!block)
            return;

        size_t rows = block.rows();
        if (!rows)
            return;

        StoragePtr destination;
        if (!storage.no_destination)
        {
            destination = storage.context.tryGetTable(storage.destination_database, storage.destination_table);

            if (destination)
            {
                if (destination.get() == &storage)
                    throw Exception("Destination table is myself. Write will cause infinite loop.", ErrorCodes::INFINITE_LOOP);

                /// Check table structure.
                try
                {
                    destination->check(block, true);
                }
                catch (Exception & e)
                {
                    e.addMessage("(when looking at destination table " + storage.destination_database + "." + storage.destination_table + ")");
                    throw;
                }
            }
        }

        size_t bytes = block.bytes();

        /// If the block already exceeds the maximum limit, then we skip the buffer.
        if (rows > storage.max_thresholds.rows || bytes > storage.max_thresholds.bytes)
        {
            if (!storage.no_destination)
            {
                LOG_TRACE(storage.log, "Writing block with " << rows << " rows, " << bytes << " bytes directly.");
                storage.writeBlockToDestination(block, destination);
             }
            return;
        }

        /// We distribute the load on the shards by the stream number.
        const auto start_shard_num = Poco::ThreadNumber::get() % storage.num_shards;

        /// We loop through the buffers, trying to lock mutex. No more than one lap.
        auto shard_num = start_shard_num;

        StorageBuffer::Buffer * least_busy_buffer = nullptr;
        std::unique_lock<std::mutex> least_busy_lock;
        size_t least_busy_shard_rows = 0;

        for (size_t try_no = 0; try_no < storage.num_shards; ++try_no)
        {
            std::unique_lock<std::mutex> lock(storage.buffers[shard_num].mutex, std::try_to_lock_t());

            if (lock.owns_lock())
            {
                size_t num_rows = storage.buffers[shard_num].data.rows();
                if (!least_busy_buffer || num_rows < least_busy_shard_rows)
                {
                    least_busy_buffer = &storage.buffers[shard_num];
                    least_busy_lock = std::move(lock);
                    least_busy_shard_rows = num_rows;
                }
            }

            shard_num = (shard_num + 1) % storage.num_shards;
        }

        /// If you still can not lock anything at once, then we'll wait on mutex.
        if (!least_busy_buffer)
            insertIntoBuffer(block, storage.buffers[start_shard_num], std::unique_lock<std::mutex>(storage.buffers[start_shard_num].mutex));
        else
            insertIntoBuffer(block, *least_busy_buffer, std::move(least_busy_lock));
    }
private:
    StorageBuffer & storage;

    void insertIntoBuffer(const Block & block, StorageBuffer::Buffer & buffer, std::unique_lock<std::mutex> && lock)
    {
        time_t current_time = time(0);

        /// Sort the columns in the block. This is necessary to make it easier to concatenate the blocks later.
        Block sorted_block = block.sortColumns();

        if (!buffer.data)
        {
            buffer.data = sorted_block.cloneEmpty();
        }
        else if (storage.checkThresholds(buffer, current_time, sorted_block.rows(), sorted_block.bytes()))
        {
            /** If, after inserting the buffer, the constraints are exceeded, then we will reset the buffer.
              * This also protects against unlimited consumption of RAM, since if it is impossible to write to the table,
              *  an exception will be thrown, and new data will not be added to the buffer.
              */

            lock.unlock();
            storage.flushBuffer(buffer, true);
            lock.lock();
        }

        if (!buffer.first_write_time)
            buffer.first_write_time = current_time;

        appendBlock(sorted_block, buffer.data);
    }
};


BlockOutputStreamPtr StorageBuffer::write(ASTPtr query, const Settings & settings)
{
    return std::make_shared<BufferBlockOutputStream>(*this);
}


void StorageBuffer::shutdown()
{
    shutdown_event.set();

    if (flush_thread.joinable())
        flush_thread.join();

    try
    {
        optimize({}, {}, context.getSettings());
    }
    catch (...)
    {
        tryLogCurrentException(__PRETTY_FUNCTION__);
    }
}


/** NOTE If you do OPTIMIZE after insertion,
  * it does not guarantee, that all data will be in destination table at the time of next SELECT just after OPTIMIZE.
  *
  * Because in case if there was already running flushBuffer method,
  *  then call to flushBuffer inside OPTIMIZE will see empty buffer and return quickly,
  *  but at the same time, the already running flushBuffer method possibly is not finished,
  *  so next SELECT will observe missing data.
  *
  * This kind of race condition make very hard to implement proper tests.
  */
bool StorageBuffer::optimize(const String & partition, bool final, const Settings & settings)
{
    if (!partition.empty())
        throw Exception("Partition cannot be specified when optimizing table of type Buffer", ErrorCodes::NOT_IMPLEMENTED);

    if (final)
        throw Exception("FINAL cannot be specified when optimizing table of type Buffer", ErrorCodes::NOT_IMPLEMENTED);

    flushAllBuffers(false);
    return true;
}


bool StorageBuffer::checkThresholds(const Buffer & buffer, time_t current_time, size_t additional_rows, size_t additional_bytes) const
{
    time_t time_passed = 0;
    if (buffer.first_write_time)
        time_passed = current_time - buffer.first_write_time;

    size_t rows = buffer.data.rows() + additional_rows;
    size_t bytes = buffer.data.bytes() + additional_bytes;

    return checkThresholdsImpl(rows, bytes, time_passed);
}


bool StorageBuffer::checkThresholdsImpl(size_t rows, size_t bytes, time_t time_passed) const
{
    if (time_passed > min_thresholds.time && rows > min_thresholds.rows && bytes > min_thresholds.bytes)
    {
        ProfileEvents::increment(ProfileEvents::StorageBufferPassedAllMinThresholds);
        return true;
    }

    if (time_passed > max_thresholds.time)
    {
        ProfileEvents::increment(ProfileEvents::StorageBufferPassedTimeMaxThreshold);
        return true;
    }

    if (rows > max_thresholds.rows)
    {
        ProfileEvents::increment(ProfileEvents::StorageBufferPassedRowsMaxThreshold);
        return true;
    }

    if (bytes > max_thresholds.bytes)
    {
        ProfileEvents::increment(ProfileEvents::StorageBufferPassedBytesMaxThreshold);
        return true;
    }

    return false;
}


void StorageBuffer::flushAllBuffers(const bool check_thresholds)
{
    for (auto & buf : buffers)
        flushBuffer(buf, check_thresholds);
}


void StorageBuffer::flushBuffer(Buffer & buffer, bool check_thresholds)
{
    Block block_to_write;
    time_t current_time = time(0);

    size_t rows = 0;
    size_t bytes = 0;
    time_t time_passed = 0;

    {
        std::lock_guard<std::mutex> lock(buffer.mutex);

        block_to_write = buffer.data.cloneEmpty();

        rows = buffer.data.rows();
        bytes = buffer.data.bytes();
        if (buffer.first_write_time)
            time_passed = current_time - buffer.first_write_time;

        if (check_thresholds)
        {
            if (!checkThresholdsImpl(rows, bytes, time_passed))
                return;
        }
        else
        {
            if (rows == 0)
                return;
        }

        buffer.data.swap(block_to_write);
        buffer.first_write_time = 0;

        CurrentMetrics::sub(CurrentMetrics::StorageBufferRows, block_to_write.rows());
        CurrentMetrics::sub(CurrentMetrics::StorageBufferBytes, block_to_write.bytes());

        ProfileEvents::increment(ProfileEvents::StorageBufferFlush);

        LOG_TRACE(log, "Flushing buffer with " << rows << " rows, " << bytes << " bytes, age " << time_passed << " seconds.");

        if (no_destination)
            return;

        /** For simplicity, buffer is locked during write.
          * We could unlock buffer temporary, but it would lead to too much difficulties:
          * - data, that is written, will not be visible for SELECTs;
          * - new data could be appended to buffer, and in case of exception, we must merge it with old data, that has not been written;
          * - this could lead to infinite memory growth.
          */
        try
        {
            writeBlockToDestination(block_to_write, context.tryGetTable(destination_database, destination_table));
        }
        catch (...)
        {
            ProfileEvents::increment(ProfileEvents::StorageBufferErrorOnFlush);

            /// Return the block to its place in the buffer.

            CurrentMetrics::add(CurrentMetrics::StorageBufferRows, block_to_write.rows());
            CurrentMetrics::add(CurrentMetrics::StorageBufferBytes, block_to_write.bytes());

            buffer.data.swap(block_to_write);

            if (!buffer.first_write_time)
                buffer.first_write_time = current_time;

            /// After a while, the next write attempt will happen.
            throw;
        }
    }
}


void StorageBuffer::writeBlockToDestination(const Block & block, StoragePtr table)
{
    if (no_destination || !block)
        return;

    if (!table)
    {
        LOG_ERROR(log, "Destination table " << destination_database << "." << destination_table << " doesn't exist. Block of data is discarded.");
        return;
    }

    auto insert = std::make_shared<ASTInsertQuery>();

    insert->database = destination_database;
    insert->table = destination_table;

    /** We will insert columns that are the intersection set of columns of the buffer table and the subordinate table.
      * This will support some of the cases (but not all) when the table structure does not match.
      */
    Block structure_of_destination_table = table->getSampleBlock();
    Names columns_intersection;
    columns_intersection.reserve(block.columns());
    for (size_t i : ext::range(0, structure_of_destination_table.columns()))
    {
        auto dst_col = structure_of_destination_table.getByPosition(i);
        if (block.has(dst_col.name))
        {
            if (block.getByName(dst_col.name).type->getName() != dst_col.type->getName())
            {
                LOG_ERROR(log, "Destination table " << destination_database << "." << destination_table
                    << " have different type of column " << dst_col.name << ". Block of data is discarded.");
                return;
            }

            columns_intersection.push_back(dst_col.name);
        }
    }

    if (columns_intersection.empty())
    {
        LOG_ERROR(log, "Destination table " << destination_database << "." << destination_table << " have no common columns with block in buffer. Block of data is discarded.");
        return;
    }

    if (columns_intersection.size() != block.columns())
        LOG_WARNING(log, "Not all columns from block in buffer exist in destination table "
            << destination_database << "." << destination_table << ". Some columns are discarded.");

    auto list_of_columns = std::make_shared<ASTExpressionList>();
    insert->columns = list_of_columns;
    list_of_columns->children.reserve(columns_intersection.size());
    for (const String & column : columns_intersection)
        list_of_columns->children.push_back(std::make_shared<ASTIdentifier>(StringRange(), column, ASTIdentifier::Column));

    InterpreterInsertQuery interpreter{insert, context};

    auto block_io = interpreter.execute();
    block_io.out->writePrefix();
    block_io.out->write(block);
    block_io.out->writeSuffix();
}


void StorageBuffer::flushThread()
{
    setThreadName("BufferFlush");

    do
    {
        try
        {
            flushAllBuffers(true);
        }
        catch (...)
        {
            tryLogCurrentException(__PRETTY_FUNCTION__);
        }
    } while (!shutdown_event.tryWait(1000));
}


void StorageBuffer::alter(const AlterCommands & params, const String & database_name, const String & table_name, const Context & context)
{
    for (const auto & param : params)
        if (param.type == AlterCommand::MODIFY_PRIMARY_KEY)
            throw Exception("Storage engine " + getName() + " doesn't support primary key.", ErrorCodes::NOT_IMPLEMENTED);

    auto lock = lockStructureForAlter();

    /// So that no blocks of the old structure remain.
    optimize({}, {}, context.getSettings());

    params.apply(*columns, materialized_columns, alias_columns, column_defaults);

    context.getDatabase(database_name)->alterTable(
        context, table_name,
        *columns, materialized_columns, alias_columns, column_defaults, {});
}

}