1 #ifndef SQL_HASH_JOIN_CHUNK_H_ 2 #define SQL_HASH_JOIN_CHUNK_H_ 3 4 /* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved. 5 6 This program is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License, version 2.0, 8 as published by the Free Software Foundation. 9 10 This program is also distributed with certain software (including 11 but not limited to OpenSSL) that is licensed under separate terms, 12 as designated in a particular file or component or in included license 13 documentation. The authors of MySQL hereby grant you an additional 14 permission to link the program and your derivative works with the 15 separately licensed software that they have included with MySQL. 16 17 This program is distributed in the hope that it will be useful, 18 but WITHOUT ANY WARRANTY; without even the implied warranty of 19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 20 GNU General Public License, version 2.0, for more details. 21 22 You should have received a copy of the GNU General Public License 23 along with this program; if not, write to the Free Software 24 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */ 25 26 #include <stddef.h> 27 28 #include "my_alloc.h" 29 #include "my_base.h" 30 #include "my_inttypes.h" 31 #include "my_sys.h" 32 #include "sql/hash_join_buffer.h" 33 34 class String; 35 36 // A HashJoinChunk is a file located on disk that can be used to store rows. 37 // It is used in on-disk hash join when a table is to be partitioned out to 38 // several smaller files, a.k.a. HashJoinChunks. 39 // 40 // When writing a column to a HashJoinChunk, we use StoreFromTableBuffers for 41 // converting the necessary columns into a format suitable for storage on disk. 42 // Conveniently, StoreFromTableBuffers creates a contiguous range of bytes and a 43 // corresponding length that easily and efficiently can be written out to the 44 // file. When reading rows back from a file, LoadIntoTableBuffers() is used to 45 // put the row back into the table record buffers. 46 // 47 // The basic usage goes like this: 48 // 49 // HashJoinChunk chunk; 50 // // Initialize a chunk to hold data from the given tables without any match 51 // // flags. 52 // chunk.Init(tables, /*uses_match_flags=*/false); 53 // String buffer; // A buffer that is used when copying data between tables 54 // // and the chunk file, and vica versa. 55 // while (iterator->Read() == 0) { 56 // // Write the row that lies in the record buffers of "tables" to this 57 // // chunk, using the provided buffer. If the chunk file was initialized to 58 // // use match flags, we would prefix the row with a match flag saying that 59 // // this row did not have any matching row. 60 // chunk.WriteRowToChunk(&buffer, /*matched=*/false); 61 // }; 62 // 63 // chunk.Rewind(); // Prepare to read the first row in this chunk. 64 // 65 // bool match_flag, 66 // // Put the row from the chunk to the record buffers of "tables", using the 67 // // provided buffer. If the chunk file was initialized to use match flags, 68 // // the match flag for the row read would be stored in 'match_flag'. 69 // chunk.LoadRowFromChunk(&buffer, &match_flag); 70 class HashJoinChunk { 71 public: 72 HashJoinChunk() = default; // Constructible. 73 74 HashJoinChunk(HashJoinChunk &&other); // Movable. 75 76 HashJoinChunk(const HashJoinChunk &obj) = delete; 77 78 HashJoinChunk &operator=(HashJoinChunk &&other); 79 80 ~HashJoinChunk(); 81 82 /// Initialize this HashJoinChunk. 83 /// 84 /// @param tables The tables to store row data from. Which column we store in 85 /// the chunk file is determined by each tables read set. 86 /// @param uses_match_flags Whether each row should be prefixed with a match 87 /// flag, saying whether the row had a matching row. 88 /// 89 /// @returns true if the initialization failed. 90 bool Init(const hash_join_buffer::TableCollection &tables, 91 bool uses_match_flags); 92 93 /// @returns the number of rows in this HashJoinChunk num_rows()94 ha_rows num_rows() const { return m_num_rows; } 95 96 /// Write a row to the HashJoinChunk. 97 /// 98 /// Read the row that lies in the record buffer (record[0]) of the given 99 /// tables and write it out to the underlying file. If the QEP_TAB signals 100 /// that the row ID should be kept, it is also written out. Note that 101 /// TABLE::read_set is used to signal which columns that should be written to 102 /// the chunk. 103 /// 104 /// @param buffer a buffer that is used when copying data from the tables to 105 /// the chunk file. Note that any existing data in "buffer" is overwritten. 106 /// @param matched whether this row has seen a matching row from the other 107 /// input. The flag is only written if 'm_uses_match_flags' is set, and if 108 /// the row comes from the probe input. 109 /// 110 /// @retval true on error. 111 bool WriteRowToChunk(String *buffer, bool matched); 112 113 /// Read a row from the HashJoinChunk and put it in the record buffer. 114 /// 115 /// The function will read a row from file on disk and put it in the record 116 /// buffers (table->record[0]) in the provided tables. The file on disk should 117 /// already be pointing to the start of a row. 118 /// 119 /// @param buffer a buffer that is used when copying data from the chunk file 120 /// to the tables. Note that any existing data in "buffer" is overwritten. 121 /// 122 /// @param[out] matched whether this row has seen a matching row from the 123 /// other input. The flag is only restored if 'm_uses_match_flags' is set, 124 /// and if the row comes from the probe input. 125 /// @retval true on error. 126 bool LoadRowFromChunk(String *buffer, bool *matched); 127 128 /// Flush the file buffer, and prepare the file for reading. 129 /// 130 /// @retval true on error 131 bool Rewind(); 132 133 private: 134 // A collection of which tables the chunk file holds data from. Used to 135 // determine where to read data from, and where to put the data back. 136 hash_join_buffer::TableCollection m_tables; 137 138 // The number of rows in this chunk file. 139 ha_rows m_num_rows{0}; 140 141 // The underlying file that is used when reading data to and from disk. 142 IO_CACHE m_file; 143 144 // Whether every row is prefixed with a match flag. 145 bool m_uses_match_flags{false}; 146 }; 147 148 #endif // SQL_HASH_JOIN_CHUNK_H_ 149