ddl0impl-merge.h

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/** @file include/ddl0impl-merge.h
 DDL cluster merge sort data structures.
 Created 2020-11-01 by Sunny Bains. */
 
#ifndef ddl0impl_merge_h
#define ddl0impl_merge_h
 
#include <vector>
 
#include "ddl0impl-file-reader.h"
 
namespace ddl {
 
// Forward declaration.
struct Builder;
 
/** Merge the blocks in the file. */
struct Merge_file_sort {
  // Forward declarations.
  struct Cursor;
  struct Output_file;
 
  /** The design is generalized as an N way merge, however we stick
  with 2 for now. */
  static constexpr size_t N_WAY_MERGE = 2;
 
  /** Context to use for merging the files/runs. */
  struct Context {
    /** File to sort. */
    ddl::file_t *m_file{};
 
    /** For reporting duplicates, it has the index instance too. */
    Dup *m_dup{};
 
    /** Number of scan threads used, for memory buffer calculation. */
    size_t m_n_threads{};
 
    /** PFS progress monitoring. */
    Alter_stage *m_stage{};
  };
 
  /** Offsets of record lists to merge. Two adjacent entries make one list or
  range */
  using Ranges = std::vector<os_offset_t>;
 
  /** Constructor.
  @param[in,out] merge_ctx      Data blocks merge meta data. */
  explicit Merge_file_sort(Context *merge_ctx) noexcept
      : m_merge_ctx(merge_ctx) {}
 
  /** Merge the the blocks.
  @param[in,out] builder        Builder instance used for building index.
  @param[in,out] offsets        Offsets from where to start the merge.
  @return DB_SUCCESS or error code. */
  [[nodiscard]] dberr_t sort(Builder *builder, Merge_offsets &offsets) noexcept;
 
  /** @return the number of rows in the sorted file. */
  [[nodiscard]] uint64_t get_n_rows() const noexcept { return m_n_rows; }
 
 private:
  /** Merge the rows.
  @param[in,out] cursor         To iterate over the rows to merge.
  @param[in,out] output_file    Output file to write the merged rows.
  @return DB_SUCCESS or error code. */
  [[nodiscard]] dberr_t merge_rows(Cursor &cursor,
                                   Output_file &output_file) noexcept;
 
  /** Merge the blocks in the ranges.
  @param[in,out] cursor         To iterate over the rows to merge.
  @param[in,out] offsets        Starting offsets of record lists to merge.
  @param[in,out] output_file    Output file to write the merged rows.
  @param[in] buffer_size        IO buffer size for reads.
  @return DB_SUCCESS or error code. */
  [[nodiscard]] dberr_t merge_ranges(Cursor &cursor, Merge_offsets &offsets,
                                     Output_file &output_file,
                                     size_t buffer_size) noexcept;
 
  /** Move to the next ranges of pages to merge.
  @param[in,out] offsets         Current offsets to start the merge from.
  @return the next range to merge. */
  Ranges next_ranges(Merge_offsets &offsets) noexcept;
 
 private:
  /** To check and report duplicates. */
  Dup *m_dup{};
 
  /** Meta data for merging blocks. */
  Context *m_merge_ctx{};
 
  /** Page numbers to merge for the next pass. */
  Merge_offsets m_next_offsets{};
 
  /** Number of rows in the sorted file. */
  uint64_t m_n_rows{};
};
 
}  // namespace ddl
 
#endif /* !ddl0impl_merge_h */