ClickHouse/src/IO/MMapReadBufferFromFileWithCache.cpp

#include <IO/MMapReadBufferFromFileWithCache.h>


namespace DB
{

namespace
{
    /// TODO: Move to a better place, make configurable.
    MappedFileCache cache(1000);
}


namespace ErrorCodes
{
    extern const int ARGUMENT_OUT_OF_BOUND;
    extern const int CANNOT_SEEK_THROUGH_FILE;
}


void MMapReadBufferFromFileWithCache::init()
{
    size_t length = mapped->getLength();
    BufferBase::set(mapped->getData(), length, 0);

    size_t page_size = static_cast<size_t>(::getPageSize());
    ReadBuffer::padded = (length % page_size) > 0 && (length % page_size) <= (page_size - 15);
}


MMapReadBufferFromFileWithCache::MMapReadBufferFromFileWithCache(
    const std::string & file_name, size_t offset, size_t length)
{
    mapped = cache.getOrSet(cache.hash(file_name, offset, length), [&]
    {
        return std::make_shared<MappedFile>(file_name, offset, length);
    }).first;

    init();
}

MMapReadBufferFromFileWithCache::MMapReadBufferFromFileWithCache(
    const std::string & file_name, size_t offset)
{
    mapped = cache.getOrSet(cache.hash(file_name, offset, -1), [&]
    {
        return std::make_shared<MappedFile>(file_name, offset);
    }).first;

    init();
}


std::string MMapReadBufferFromFileWithCache::getFileName() const
{
    return mapped->getFileName();
}

off_t MMapReadBufferFromFileWithCache::getPosition()
{
    return count();
}

off_t MMapReadBufferFromFileWithCache::seek(off_t offset, int whence)
{
    off_t new_pos;
    if (whence == SEEK_SET)
        new_pos = offset;
    else if (whence == SEEK_CUR)
        new_pos = count() + offset;
    else
        throw Exception("MMapReadBufferFromFileWithCache::seek expects SEEK_SET or SEEK_CUR as whence", ErrorCodes::ARGUMENT_OUT_OF_BOUND);

    working_buffer = internal_buffer;
    if (new_pos < 0 || new_pos > off_t(working_buffer.size()))
        throw Exception("Cannot seek through file " + getFileName()
            + " because seek position (" + toString(new_pos) + ") is out of bounds [0, " + toString(working_buffer.size()) + "]",
            ErrorCodes::CANNOT_SEEK_THROUGH_FILE);

    position() = working_buffer.begin() + new_pos;
    return new_pos;
}

}