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46 lines
1.3 KiB
C++
46 lines
1.3 KiB
C++
#pragma once
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#include "config.h"
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#include <Storages/IStorage.h>
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namespace DB
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{
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struct ExternalDataSourceConfiguration;
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/// Storages MySQL and PostgreSQL use ConnectionPoolWithFailover and support multiple replicas.
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/// This class unites multiple storages with replicas into multiple shards with replicas.
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/// A query to external database is passed to one replica on each shard, the result is united.
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/// Replicas on each shard have the same priority, traversed replicas are moved to the end of the queue.
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/// Similar approach is used for URL storage.
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class StorageExternalDistributed final : public DB::IStorage
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{
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public:
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StorageExternalDistributed(
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const StorageID & table_id_,
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std::unordered_set<StoragePtr> && shards_,
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const ColumnsDescription & columns_,
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const ConstraintsDescription & constraints_,
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const String & comment);
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std::string getName() const override { return "ExternalDistributed"; }
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void read(
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QueryPlan & query_plan,
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const Names & column_names,
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const StorageSnapshotPtr & storage_snapshot,
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SelectQueryInfo & query_info,
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ContextPtr context,
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QueryProcessingStage::Enum processed_stage,
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size_t max_block_size,
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size_t num_streams) override;
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private:
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using Shards = std::unordered_set<StoragePtr>;
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Shards shards;
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};
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}
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