ClickHouse/src/Storages/MergeTree/MergeTreeReverseSelectProcessor.cpp

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#include <Storages/MergeTree/MergeTreeReverseSelectProcessor.h>
namespace DB
{
namespace ErrorCodes
{
extern const int MEMORY_LIMIT_EXCEEDED;
}
bool MergeTreeReverseSelectProcessor::getNewTaskImpl()
try
{
if (chunks.empty() && all_mark_ranges.empty())
return false;
/// We have some blocks to return in buffer.
/// Return true to continue reading, but actually don't create a task.
if (all_mark_ranges.empty())
return true;
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if (!reader)
initializeReaders();
/// Read ranges from right to left.
MarkRanges mark_ranges_for_task = { all_mark_ranges.back() };
all_mark_ranges.pop_back();
auto size_predictor = (preferred_block_size_bytes == 0) ? nullptr
: getSizePredictor(data_part, task_columns, sample_block);
task = std::make_unique<MergeTreeReadTask>(
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data_part, mark_ranges_for_task, part_index_in_query, ordered_names, column_name_set,
task_columns, prewhere_info && prewhere_info->remove_prewhere_column,
std::move(size_predictor));
return true;
}
catch (...)
{
/// Suspicion of the broken part. A part is added to the queue for verification.
if (getCurrentExceptionCode() != ErrorCodes::MEMORY_LIMIT_EXCEEDED)
storage.reportBrokenPart(data_part);
throw;
}
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MergeTreeBaseSelectProcessor::BlockAndRowCount MergeTreeReverseSelectProcessor::readFromPart()
{
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BlockAndRowCount res;
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if (!chunks.empty())
{
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res = std::move(chunks.back());
chunks.pop_back();
return res;
}
if (!task->range_reader.isInitialized())
initializeRangeReaders(*task);
while (!task->isFinished())
{
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auto chunk = readFromPartImpl();
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chunks.push_back(std::move(chunk));
}
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if (chunks.empty())
return {};
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res = std::move(chunks.back());
chunks.pop_back();
return res;
}
}