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https://github.com/ClickHouse/ClickHouse.git
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Less seeks in compressed buffers
This commit is contained in:
parent
dab4c60596
commit
8186339307
@ -2,6 +2,7 @@
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#include <IO/WriteHelpers.h>
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#include <Compression/LZ4_decompress_faster.h>
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#include <common/logger_useful.h>
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#include <utility>
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@ -30,7 +31,6 @@ void CachedCompressedReadBuffer::initInput()
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bool CachedCompressedReadBuffer::nextImpl()
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{
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/// Let's check for the presence of a decompressed block in the cache, grab the ownership of this block, if it exists.
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UInt128 key = cache->hash(path, file_pos);
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@ -60,6 +60,13 @@ bool CachedCompressedReadBuffer::nextImpl()
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working_buffer = Buffer(owned_cell->data.data(), owned_cell->data.data() + owned_cell->data.size() - owned_cell->additional_bytes);
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/// nextimpl_working_buffer_offset is set in the seek function (lazy seek). So we have to
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/// check that we are not seeking beyond working buffer.
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if (nextimpl_working_buffer_offset > working_buffer.size())
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throw Exception("Seek position is beyond the decompressed block"
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" (pos: " + toString(nextimpl_working_buffer_offset) + ", block size: " + toString(working_buffer.size()) + ")",
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ErrorCodes::SEEK_POSITION_OUT_OF_BOUND);
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file_pos += owned_cell->compressed_size;
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return true;
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@ -74,28 +81,32 @@ CachedCompressedReadBuffer::CachedCompressedReadBuffer(
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void CachedCompressedReadBuffer::seek(size_t offset_in_compressed_file, size_t offset_in_decompressed_block)
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{
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/// Nothing to do if we already at required position
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if (file_pos == offset_in_compressed_file
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&& (offset() == offset_in_decompressed_block ||
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nextimpl_working_buffer_offset == offset_in_decompressed_block))
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return;
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if (owned_cell &&
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offset_in_compressed_file == file_pos - owned_cell->compressed_size &&
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offset_in_decompressed_block <= working_buffer.size())
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{
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bytes += offset();
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pos = working_buffer.begin() + offset_in_decompressed_block;
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bytes -= offset();
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}
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else
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{
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LOG_INFO(&Poco::Logger::get("DEBUG"), "Adding offset {}", offset());
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/// Remember position in compressed file (will be moved in nextImpl)
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file_pos = offset_in_compressed_file;
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/// We will discard our working_buffer, but have to account rest bytes
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bytes += offset();
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nextImpl();
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if (offset_in_decompressed_block > working_buffer.size())
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throw Exception("Seek position is beyond the decompressed block"
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" (pos: " + toString(offset_in_decompressed_block) + ", block size: " + toString(working_buffer.size()) + ")",
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ErrorCodes::SEEK_POSITION_OUT_OF_BOUND);
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pos = working_buffer.begin() + offset_in_decompressed_block;
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bytes -= offset();
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/// No data, everything discarded
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pos = working_buffer.end();
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/// Remember required offset in decompressed block which will be set in
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/// the next ReadBuffer::next() call
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nextimpl_working_buffer_offset = offset_in_decompressed_block;
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}
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}
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@ -15,7 +15,7 @@ namespace DB
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* The external cache is passed as an argument to the constructor.
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* Allows you to increase performance in cases where the same blocks are often read.
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* Disadvantages:
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* - in case you need to read a lot of data in a row, but of them only a part is cached, you have to do seek-and.
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* - in case you need to read a lot of data in a row, but some of them only a part is cached, you have to do seek-and.
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*/
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class CachedCompressedReadBuffer : public CompressedReadBufferBase, public ReadBuffer
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{
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@ -25,6 +25,8 @@ private:
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std::unique_ptr<ReadBufferFromFileBase> file_in;
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const std::string path;
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/// Current position in file_in
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size_t file_pos;
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/// A piece of data from the cache, or a piece of read data that we put into the cache.
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@ -37,9 +39,15 @@ private:
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ReadBufferFromFileBase::ProfileCallback profile_callback;
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clockid_t clock_type {};
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/// Check comment in CompressedReadBuffer
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/* size_t nextimpl_working_buffer_offset; */
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public:
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CachedCompressedReadBuffer(const std::string & path, std::function<std::unique_ptr<ReadBufferFromFileBase>()> file_in_creator, UncompressedCache * cache_, bool allow_different_codecs_ = false);
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/// Seek is lazy. It doesn't move the position anywhere, just remember them and perform actual
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/// seek inside nextImpl.
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void seek(size_t offset_in_compressed_file, size_t offset_in_decompressed_block);
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void setProfileCallback(const ReadBufferFromFileBase::ProfileCallback & profile_callback_, clockid_t clock_type_ = CLOCK_MONOTONIC_COARSE)
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@ -33,6 +33,13 @@ bool CompressedReadBufferFromFile::nextImpl()
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decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
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/// nextimpl_working_buffer_offset is set in the seek function (lazy seek). So we have to
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/// check that we are not seeking beyond working buffer.
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if (nextimpl_working_buffer_offset > working_buffer.size())
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throw Exception("Required to move position beyond the decompressed block"
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" (pos: " + toString(nextimpl_working_buffer_offset) + ", block size: " + toString(working_buffer.size()) + ")",
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ErrorCodes::SEEK_POSITION_OUT_OF_BOUND);
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return true;
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}
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@ -67,33 +74,34 @@ CompressedReadBufferFromFile::CompressedReadBufferFromFile(
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void CompressedReadBufferFromFile::seek(size_t offset_in_compressed_file, size_t offset_in_decompressed_block)
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{
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/// Nothing to do if we already at required position
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if (file_in.getPosition() - size_compressed == offset_in_compressed_file && /// correct position in compressed file
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(offset() == offset_in_decompressed_block /// correct position in buffer or
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|| nextimpl_working_buffer_offset == offset_in_decompressed_block)) /// we will move our position to correct one
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return;
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/// Our seek is within working_buffer, so just move the position
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if (size_compressed &&
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offset_in_compressed_file == file_in.getPosition() - size_compressed &&
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offset_in_decompressed_block <= working_buffer.size())
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{
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bytes += offset();
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pos = working_buffer.begin() + offset_in_decompressed_block;
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/// `bytes` can overflow and get negative, but in `count()` everything will overflow back and get right.
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bytes -= offset();
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}
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else
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else /// Our seek outside working buffer, so perform "lazy seek"
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{
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/// Actually seek compressed file
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file_in.seek(offset_in_compressed_file, SEEK_SET);
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/// We will discard our working_buffer, but have to account rest bytes
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bytes += offset();
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nextImpl();
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if (offset_in_decompressed_block > working_buffer.size())
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throw Exception("Seek position is beyond the decompressed block"
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" (pos: " + toString(offset_in_decompressed_block) + ", block size: " + toString(working_buffer.size()) + ")",
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ErrorCodes::SEEK_POSITION_OUT_OF_BOUND);
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pos = working_buffer.begin() + offset_in_decompressed_block;
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bytes -= offset();
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/// No data, everything discarded
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pos = working_buffer.end();
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size_compressed = 0;
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/// Remember required offset in decompressed block which will be set in
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/// the next ReadBuffer::next() call
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nextimpl_working_buffer_offset = offset_in_decompressed_block;
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}
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}
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size_t CompressedReadBufferFromFile::readBig(char * to, size_t n)
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{
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size_t bytes_read = 0;
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@ -134,7 +142,11 @@ size_t CompressedReadBufferFromFile::readBig(char * to, size_t n)
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working_buffer = Buffer(memory.data(), &memory[size_decompressed]);
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decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
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pos = working_buffer.begin();
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/// Manually take nextimpl_working_buffer_offset into account, because we don't use
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/// nextImpl in this method.
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pos = working_buffer.begin() + nextimpl_working_buffer_offset;
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nextimpl_working_buffer_offset = 0;
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bytes_read += read(to + bytes_read, n - bytes_read);
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break;
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@ -28,6 +28,19 @@ private:
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ReadBufferFromFileBase & file_in;
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size_t size_compressed = 0;
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/// This field inherited from ReadBuffer. It's used to perform "lazy" seek, so in seek() call we:
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/// 1) actually seek only underlying compressed file_in to offset_in_compressed_file;
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/// 2) reset current working_buffer;
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/// 3) remember the position in decompressed block in nextimpl_working_buffer_offset.
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/// After following ReadBuffer::next() -> nextImpl call we will read new data into working_buffer and
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/// ReadBuffer::next() will move our position in the fresh working_buffer to nextimpl_working_buffer_offset and
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/// reset it to zero.
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///
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/// NOTE: We have independent readBig implementation, so we have to take
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/// nextimpl_working_buffer_offset into account there as well.
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///
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/* size_t nextimpl_working_buffer_offset; */
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bool nextImpl() override;
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void prefetch() override;
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@ -37,6 +50,9 @@ public:
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CompressedReadBufferFromFile(
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const std::string & path, const ReadSettings & settings, size_t estimated_size, bool allow_different_codecs_ = false);
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/// Seek is lazy in some sense. We move position in compressed file_in to offset_in_compressed_file, but don't
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/// read data into working_buffer and don't shit our position to offset_in_decompressed_block. Instead
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/// we store this offset inside nextimpl_working_buffer_offset.
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void seek(size_t offset_in_compressed_file, size_t offset_in_decompressed_block);
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size_t readBig(char * to, size_t n) override;
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@ -75,6 +75,7 @@ size_t MergeTreeReaderWide::readRows(size_t from_mark, bool continue_reading, si
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OffsetColumns offset_columns;
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std::unordered_map<String, ISerialization::SubstreamsCache> caches;
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std::unordered_set<std::string> prefetched_streams;
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if (disk->isRemote() ? settings.read_settings.remote_fs_prefetch : settings.read_settings.local_fs_prefetch)
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{
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/// Request reading of data in advance,
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@ -86,7 +87,7 @@ size_t MergeTreeReaderWide::readRows(size_t from_mark, bool continue_reading, si
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try
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{
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auto & cache = caches[column_from_part.getNameInStorage()];
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prefetch(column_from_part, from_mark, continue_reading, cache);
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prefetch(column_from_part, from_mark, continue_reading, cache, prefetched_streams);
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}
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catch (Exception & e)
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{
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@ -98,6 +99,7 @@ size_t MergeTreeReaderWide::readRows(size_t from_mark, bool continue_reading, si
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}
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auto name_and_type = columns.begin();
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for (size_t pos = 0; pos < num_columns; ++pos, ++name_and_type)
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{
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auto column_from_part = getColumnFromPart(*name_and_type);
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@ -114,7 +116,9 @@ size_t MergeTreeReaderWide::readRows(size_t from_mark, bool continue_reading, si
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size_t column_size_before_reading = column->size();
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auto & cache = caches[column_from_part.getNameInStorage()];
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readData(column_from_part, column, from_mark, continue_reading, max_rows_to_read, cache);
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readData(
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column_from_part, column, from_mark, continue_reading,
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max_rows_to_read, cache, /* was_prefetched =*/ !prefetched_streams.empty());
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/// For elements of Nested, column_size_before_reading may be greater than column size
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/// if offsets are not empty and were already read, but elements are empty.
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@ -190,11 +194,11 @@ void MergeTreeReaderWide::addStreams(const NameAndTypePair & name_and_type,
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static ReadBuffer * getStream(
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bool stream_for_prefix,
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bool seek_to_start,
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const ISerialization::SubstreamPath & substream_path,
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MergeTreeReaderWide::FileStreams & streams,
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const NameAndTypePair & name_and_type,
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size_t from_mark, bool continue_reading,
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size_t from_mark, bool seek_to_mark,
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ISerialization::SubstreamsCache & cache)
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{
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/// If substream have already been read.
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@ -209,9 +213,9 @@ static ReadBuffer * getStream(
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MergeTreeReaderStream & stream = *it->second;
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if (stream_for_prefix)
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if (seek_to_start)
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stream.seekToStart();
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else if (!continue_reading)
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else if (seek_to_mark)
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stream.seekToMark(from_mark);
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return stream.data_buffer;
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@ -222,15 +226,25 @@ void MergeTreeReaderWide::prefetch(
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const NameAndTypePair & name_and_type,
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size_t from_mark,
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bool continue_reading,
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ISerialization::SubstreamsCache & cache)
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ISerialization::SubstreamsCache & cache,
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std::unordered_set<std::string> & prefetched_streams)
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{
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const auto & name = name_and_type.name;
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auto & serialization = serializations[name];
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serialization->enumerateStreams([&](const ISerialization::SubstreamPath & substream_path)
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{
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if (ReadBuffer * buf = getStream(false, substream_path, streams, name_and_type, from_mark, continue_reading, cache))
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bool seek_to_start = deserialize_binary_bulk_state_map.count(name) == 0;
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String stream_name = ISerialization::getFileNameForStream(name_and_type, substream_path);
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if (!prefetched_streams.count(stream_name))
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{
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bool seek_to_mark = !continue_reading;
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if (ReadBuffer * buf = getStream(seek_to_start, substream_path, streams, name_and_type, from_mark, seek_to_mark, cache))
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buf->prefetch();
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prefetched_streams.insert(stream_name);
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}
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});
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}
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@ -238,7 +252,7 @@ void MergeTreeReaderWide::prefetch(
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void MergeTreeReaderWide::readData(
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const NameAndTypePair & name_and_type, ColumnPtr & column,
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size_t from_mark, bool continue_reading, size_t max_rows_to_read,
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ISerialization::SubstreamsCache & cache)
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ISerialization::SubstreamsCache & cache, bool was_prefetched)
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{
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double & avg_value_size_hint = avg_value_size_hints[name_and_type.name];
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ISerialization::DeserializeBinaryBulkSettings deserialize_settings;
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@ -251,14 +265,21 @@ void MergeTreeReaderWide::readData(
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{
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deserialize_settings.getter = [&](const ISerialization::SubstreamPath & substream_path)
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{
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return getStream(true, substream_path, streams, name_and_type, from_mark, continue_reading, cache);
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/// If data was already prefetched we don't need to seek to start
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bool seek_to_start = !was_prefetched;
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bool seek_to_mark = !was_prefetched && !continue_reading;
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return getStream(seek_to_start, substream_path, streams, name_and_type, from_mark, seek_to_mark, cache);
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};
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serialization->deserializeBinaryBulkStatePrefix(deserialize_settings, deserialize_binary_bulk_state_map[name]);
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}
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deserialize_settings.getter = [&](const ISerialization::SubstreamPath & substream_path)
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{
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return getStream(false, substream_path, streams, name_and_type, from_mark, continue_reading, cache);
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bool seek_to_mark = !was_prefetched && !continue_reading;
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return getStream(
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/* seek_to_start = */false, substream_path, streams, name_and_type, from_mark,
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seek_to_mark, cache);
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};
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deserialize_settings.continuous_reading = continue_reading;
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auto & deserialize_state = deserialize_binary_bulk_state_map[name];
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@ -46,14 +46,15 @@ private:
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void readData(
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const NameAndTypePair & name_and_type, ColumnPtr & column,
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size_t from_mark, bool continue_reading, size_t max_rows_to_read,
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ISerialization::SubstreamsCache & cache);
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ISerialization::SubstreamsCache & cache, bool was_prefetched);
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/// Make next readData more simple by calling 'prefetch' of all related ReadBuffers.
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/// Make next readData more simple by calling 'prefetch' of all related ReadBuffers (column streams).
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void prefetch(
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const NameAndTypePair & name_and_type,
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size_t from_mark,
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bool continue_reading,
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ISerialization::SubstreamsCache & cache);
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ISerialization::SubstreamsCache & cache,
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std::unordered_set<std::string> & prefetched_streams); /// if stream was already prefetched do nothing
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};
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}
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