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44 lines
1.3 KiB
C++
44 lines
1.3 KiB
C++
#pragma once
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#include <ext/shared_ptr_helper.h>
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#include <optional>
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#include <Storages/IStorage.h>
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namespace DB
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{
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/** Implements a table engine for the system table "zeros".
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* The table contains the only column zero UInt8.
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* From this table, you can read non-materialized zeros.
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*
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* You could also specify a limit (how many zeros to give).
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* If multithreaded is specified, zeros will be generated in several streams.
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*/
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class StorageSystemZeros final : public ext::shared_ptr_helper<StorageSystemZeros>, public IStorage
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{
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friend struct ext::shared_ptr_helper<StorageSystemZeros>;
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public:
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std::string getName() const override { return "SystemZeros"; }
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Pipes read(
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const Names & column_names,
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const SelectQueryInfo & query_info,
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const Context & context,
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QueryProcessingStage::Enum processed_stage,
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size_t max_block_size,
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unsigned num_streams) override;
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bool hasEvenlyDistributedRead() const override { return true; }
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private:
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bool multithreaded;
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std::optional<UInt64> limit;
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protected:
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/// If even_distribution is true, numbers are distributed evenly between streams.
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/// Otherwise, streams concurrently increment atomic.
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StorageSystemZeros(const StorageID & table_id_, bool multithreaded_, std::optional<UInt64> limit_ = std::nullopt);
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};
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}
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