pack_rows.h

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#ifndef SQL_PACK_ROWS_H_
#define SQL_PACK_ROWS_H_
 
/* Copyright (c) 2020, 2022, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
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/**
  @file
 
  Generic routines for packing rows (possibly from multiple tables
  at the same time) into strings, and then back again. Used for (at least)
  hash join, BKA, and streaming aggregation.
 */
 
#include <assert.h>
#include <stddef.h>
#include <string.h>
 
#include "field_types.h"
#include "my_bitmap.h"
#include "my_compiler.h"
 
#include "my_inttypes.h"
#include "my_table_map.h"
#include "mysql/components/services/bits/psi_bits.h"
#include "prealloced_array.h"
#include "sql/field.h"
#include "sql/handler.h"
#include "sql/table.h"
#include "template_utils.h"
 
class JOIN;
class String;
 
// Names such as “Column” and “Table” are a tad too generic for the global
// namespace.
namespace pack_rows {
 
/// A class that represents a field, which also holds a cached value of the
/// field's data type.
struct Column {
  explicit Column(Field *field);
  Field *const field;
 
  // The field type is used frequently, and caching it gains around 30% in some
  // of our microbenchmarks.
  const enum_field_types field_type;
};
 
/// This struct is primarily used for holding the extracted columns in a hash
/// join. When the hash join iterator is constructed, we extract the columns
/// that are needed to satisfy the SQL query.
struct Table {
  explicit Table(TABLE *tab);
  TABLE *table;
  Prealloced_array<Column, 8> columns;
 
  // Whether to copy the NULL flags or not.
  bool copy_null_flags{false};
};
 
/// A structure that contains a list of tables for the hash join operation,
/// and some pre-computed properties for the tables.
class TableCollection {
 public:
  TableCollection() = default;
 
  TableCollection(const Prealloced_array<TABLE *, 4> &tables, bool store_rowids,
                  table_map tables_to_get_rowid_for);
 
  // A single table (typically one for which there is no map bit).
  explicit TableCollection(TABLE *table) { AddTable(table); }
 
  const Prealloced_array<Table, 4> &tables() const { return m_tables; }
 
  table_map tables_bitmap() const { return m_tables_bitmap; }
 
  size_t ref_and_null_bytes_size() const { return m_ref_and_null_bytes_size; }
 
  bool has_blob_column() const { return m_has_blob_column; }
 
  bool store_rowids() const { return m_store_rowids; }
 
  table_map tables_to_get_rowid_for() const {
    return m_tables_to_get_rowid_for;
  }
 
 private:
  void AddTable(TABLE *tab);
 
  Prealloced_array<Table, 4> m_tables{PSI_NOT_INSTRUMENTED};
 
  // We frequently use the bitmap to determine which side of the join an Item
  // belongs to, so precomputing the bitmap saves quite some time.
  table_map m_tables_bitmap = 0;
 
  // Sum of the NULL bytes and the row ID for all of the tables.
  size_t m_ref_and_null_bytes_size = 0;
 
  // Whether any of the tables has a BLOB/TEXT column. This is used to determine
  // whether we need to estimate the row size every time we store a row to the
  // row buffer or to a chunk file on disk. If this is set to false, we can
  // pre-allocate any necessary buffers we need during the hash join, and thus
  // eliminate the need for recalculating the row size every time.
  bool m_has_blob_column = false;
 
  bool m_store_rowids = false;
  table_map m_tables_to_get_rowid_for = 0;
};
 
/// Count up how many bytes a single row from the given tables will occupy,
/// in "packed" format. Note that this is an upper bound, so the length after
/// calling Field::pack may very well be shorter than the size returned by this
/// function.
///
/// The value returned from this function will sum up
/// 1) The row-id if that is to be kept.
/// 2) Size of the NULL flags.
/// 3) Size of the buffer returned by pack() on all columns marked in the
///    read_set.
///
/// Note that if any of the tables has a BLOB/TEXT column, this function looks
/// at the data stored in the record buffers. This means that the function can
/// not be called before reading any rows if tables.has_blob_column is true.
size_t ComputeRowSizeUpperBound(const TableCollection &tables);
 
/// Take the data marked for reading in "tables" and store it in the provided
/// buffer. What data to store is determined by the read set of each table.
/// Note that any existing data in "buffer" will be overwritten.
///
/// The output buffer will contain three things:
///
/// 1) NULL flags for each nullable column.
/// 2) The row ID for each row. This is only stored if QEP_TAB::rowid_status !=
///    NO_ROWID_NEEDED.
/// 3) The actual data from the columns.
///
/// @retval true if error, false otherwise
bool StoreFromTableBuffers(const TableCollection &tables, String *buffer);
 
/// Take the data in "ptr" and put it back to the tables' record buffers.
/// The tables must be _exactly_ the same as when the row was created.
/// That is, it must contain the same tables in the same order, and the read set
/// of each table must be identical when storing and restoring the row.
/// If that's not the case, you will end up with undefined and unpredictable
/// behavior.
///
/// Returns a pointer to where we ended reading.
const uchar *LoadIntoTableBuffers(const TableCollection &tables,
                                  const uchar *ptr);
 
/// For each of the given tables, request that the row ID is filled in
/// (the equivalent of calling file->position()) if needed.
///
/// @param tables All tables involved in the hash join.
/// @param tables_to_get_rowid_for A bitmap of which tables to actually
///     get row IDs for. (A table needs to be in both sets to be processed.)
void RequestRowId(const Prealloced_array<pack_rows::Table, 4> &tables,
                  table_map tables_to_get_rowid_for);
 
void PrepareForRequestRowId(const Prealloced_array<pack_rows::Table, 4> &tables,
                            table_map tables_to_get_rowid_for);
 
static bool ShouldCopyRowId(const TABLE *table) {
  // It is not safe to copy the row ID if we have a NULL-complemented row; the
  // value is undefined, or the buffer location can even be nullptr.
  return !table->const_table && !(table->is_nullable() && table->null_row);
}
 
static ALWAYS_INLINE uchar *StoreFromTableBuffersRaw(
    const TableCollection &tables, uchar *dptr) {
  for (const Table &tbl : tables.tables()) {
    const TABLE *table = tbl.table;
 
    // Store the NULL flags.
    if (tbl.copy_null_flags) {
      memcpy(dptr, table->null_flags, table->s->null_bytes);
      dptr += table->s->null_bytes;
    }
 
    if (tbl.table->is_nullable()) {
      const size_t null_row_size = sizeof(tbl.table->null_row);
      memcpy(dptr, pointer_cast<const uchar *>(&tbl.table->null_row),
             null_row_size);
      dptr += null_row_size;
    }
 
    if (tables.store_rowids() && ShouldCopyRowId(tbl.table)) {
      // Store the row ID, since it is needed by weedout.
      memcpy(dptr, table->file->ref, table->file->ref_length);
      dptr += table->file->ref_length;
    }
 
    for (const Column &column : tbl.columns) {
      assert(bitmap_is_set(column.field->table->read_set,
                           column.field->field_index()));
      if (!column.field->is_null()) {
        // Store the data in packed format. The packed format will also
        // include the length of the data if needed.
        dptr = column.field->pack(dptr);
      }
    }
  }
  return dptr;
}
 
}  // namespace pack_rows
 
#endif  // SQL_HASH_JOIN_BUFFER_H_