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  1. MariaDB Server
  2. MDEV-25449

Add MY_COLLATION_HANDLER::strnncollsp_nchars()

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    Description

      2022-01-21 Update

      This problem was solved under terms of MDEV-25904

      Old description

      Field_string::cmp() seems to do unnecessary work trimming trailing spaces:

      int Field_string::cmp(const uchar *a_ptr, const uchar *b_ptr) const
      		 
      {
      		 
        size_t a_len, b_len;
      		 
       
      		 
        if (mbmaxlen() != 1)
      		 
        {
      		 
          size_t char_len= Field_string::char_length();
      		 
          a_len= field_charset()->charpos(a_ptr, a_ptr + field_length, char_len);
      		 
          b_len= field_charset()->charpos(b_ptr, b_ptr + field_length, char_len);
      		 
        }
      		 
        else
      		 
          a_len= b_len= field_length;
      		 
        /*
      		 
          We have to remove end space to be able to compare multi-byte-characters
      		 
          like in latin_de 'ae' and 0xe4
      		 
        */
      		 
        return field_charset()->strnncollsp(a_ptr, a_len,
      		 
                                            b_ptr, b_len);
      		 
      }

      In absolute majority cases, the difference between strings is found in the very beginning of the compared strings. So doing charpos() on the two arguments, before passing them to the actual comparison function, looks like an inefficient waste of CPU.

      A better approach would be to implement a new comparison function with this tentative API:

      int strnncollsp_nchars(CHARSET_INFO *cs,
      		 
                             const char *s1, size_t len1,
      		 
                             const char *s2, size_t len2,
      		 
                             size_t nchars);

      Internally, the exact virtial implementations of strnncollsp_nchars() would do the same with what strnncollsp() do in the same collation, but with an extra limit on "nchars".

      This new function should also help to fix a bug in the similar code in InnoDB: see MDEV-25440 for details.

      Attachments

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          duplicates

          Bug - A problem which impairs or prevents the functions of the product. MDEV-25904 New collation functions to compare InnoDB style trimmed NO PAD strings

          • Major - Major loss of function.
          • Closed
          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-25440 Assertion `cmp_rec_rec(rec, old_rec, offsets, old_offsets, m_index) > 0' failed in PageBulk::insert

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-26743 InnoDB: CHAR+nopad does not work well

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-26744 MyISAM, Aria, MEMORY: CHAR+nopad does not work well

          • Major - Major loss of function.
          • Open

          Task - A task that needs to be done. MDEV-9711 NO PAD collations

          • Major - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-25904 New collation functions to compare InnoDB style trimmed NO PAD strings

          • Major - Major loss of function.
          • Closed

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              bar Alexander Barkov
              bar Alexander Barkov
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                Updated:
                Resolved:

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