mirror of
https://github.com/ClickHouse/ClickHouse.git
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98 lines
3.2 KiB
C++
98 lines
3.2 KiB
C++
#pragma once
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#include <Columns/IColumn.h>
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#include <QueryPipeline/QueryPipeline.h>
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#include <vector>
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#include <atomic>
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namespace DB
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{
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class IDictionarySource;
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using DictionarySourcePtr = std::shared_ptr<IDictionarySource>;
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/** Data-provider interface for external dictionaries,
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* abstracts out the data source (file, MySQL, ClickHouse, external program, network request et cetera)
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* from the presentation and memory layout (the dictionary itself).
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*/
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class IDictionarySource
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{
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public:
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/// Returns a pipe with all the data available from this source.
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virtual QueryPipeline loadAll() = 0;
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/// Returns a pipe with updated data available from this source.
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virtual QueryPipeline loadUpdatedAll() = 0;
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/**
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* result_size_hint - approx number of rows in the stream.
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* Returns a pipe with all the data available from this source.
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*
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* NOTE: result_size_hint may be changed during you are reading (usually it
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* will be non zero for the first block and zero for others, since it uses
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* Progress::total_rows_approx,) from the pipe, and may be called
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* in parallel, so you should use something like this:
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*
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* ...
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* std::atomic<uint64_t> new_size = 0;
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*
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* QueryPipeline pipeline;
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* pipeline.init(source->loadAll(&new_size));
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* PullingPipelineExecutor executor;
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*
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* Block block;
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* while (executor.pull(block))
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* {
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* if (new_size)
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* {
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* size_t current_new_size = new_size.exchange(0);
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* if (current_new_size)
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* resize(current_new_size);
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* }
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* else
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* {
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* resize(block.rows());
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* }
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* }
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*
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* ...
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*/
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virtual QueryPipeline loadAllWithSizeHint(std::atomic<size_t> * /* result_size_hint */)
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{
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return loadAll();
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}
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/** Indicates whether this source supports "random access" loading of data
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* loadId and loadIds can only be used if this function returns true.
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*/
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virtual bool supportsSelectiveLoad() const = 0;
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/** Returns an input stream with the data for a collection of identifiers.
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* It must be guaranteed, that 'ids' array will live at least until all data will be read from returned stream.
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*/
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virtual QueryPipeline loadIds(const std::vector<UInt64> & ids) = 0;
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/** Returns an input stream with the data for a collection of composite keys.
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* `requested_rows` contains indices of all rows containing unique keys.
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* It must be guaranteed, that 'requested_rows' array will live at least until all data will be read from returned stream.
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*/
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virtual QueryPipeline loadKeys(const Columns & key_columns, const std::vector<size_t> & requested_rows) = 0;
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/// indicates whether the source has been modified since last load* operation
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virtual bool isModified() const = 0;
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/// Returns true if update field is defined
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virtual bool hasUpdateField() const = 0;
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virtual DictionarySourcePtr clone() const = 0;
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/// returns an informal string describing the source
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virtual std::string toString() const = 0;
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virtual ~IDictionarySource() = default;
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};
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}
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