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48 lines
1.9 KiB
C++
48 lines
1.9 KiB
C++
/*
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* Copyright (C) 2022-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.1
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*/
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#pragma once
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#include <memory>
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#include "query/query-request.hh"
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class mutation_reader;
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namespace query {
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struct max_result_size;
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}
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/// A reader that emits partitions in native reverse order.
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///
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/// 1. The reader's schema() method will return a reversed schema (see
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/// \ref schema::make_reversed()).
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/// 2. Static row is still emitted first.
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/// 3. Clustering elements are emitted in reverse order.
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/// 3. Range tombstones changes' tombstones are shifted by one to the left to
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/// account for the implicit null tombstone at the start of the stream moving
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/// from start to end (due to reversing).
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/// Ordering of partitions themselves remains unchanged.
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/// For more details see docs/dev/reverse-reads.md.
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///
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/// The reader's schema (returned by `schema()`) is the reverse of `original`'s schema.
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///
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/// \param original the reader to be reversed.
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/// \param max_size the maximum amount of memory the reader is allowed to use
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/// for reversing and conversely the maximum size of the results. The
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/// reverse reader reads entire partitions into memory, before reversing
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/// them. Since partitions can be larger than the available memory, we need
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/// to enforce a limit on memory consumption. When reaching the soft limit
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/// a warning will be logged. When reaching the hard limit the read will be
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/// aborted.
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/// \param slice serves as a convenience slice storage for reads that have to
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/// store an edited slice somewhere. This is common for reads that work
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/// with a native-reversed slice and so have to convert the one used in the
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/// query -- which is in reversed format.
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mutation_reader
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make_reversing_reader(mutation_reader original, query::max_result_size max_size, std::unique_ptr<query::partition_slice> slice = {});
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