Commit 02dc7bfb authored by unknown's avatar unknown
Browse files

BUG#9622: post-review-fixes: better comments

parent 71fdef4d

include/myisam.h

+1 −1
Original line number Diff line number Diff line
@@ -323,7 +323,7 @@ typedef enum 
  MI_STATS_METHOD_NULLS_NOT_EQUAL,

  /* Treat NULLs as equal when collecting statistics (like 4.0 did) */

  MI_STATS_METHOD_NULLS_EQUAL,

  /* Ignore NULLs - count tuples without NULLs only */

  /* Ignore NULLs - count only tuples without NULLs in the index components */

  MI_STATS_METHOD_IGNORE_NULLS

} enum_mi_stats_method;

myisam/mi_check.c

+32 −22
Original line number Diff line number Diff line
@@ -603,10 +603,11 @@ void mi_collect_stats_nonulls_first(HA_KEYSEG *keyseg, ulonglong *notnull, 
    Process the next index tuple:

    1. Find out which prefix tuples of last_key don't contain NULLs, and

       update the array of notnull counters accordingly.

    2. Find the first keypart number where the tuples are different(A), or

       last_key has NULL value (B), and return it, so caller can count

       number of unique tuples for each key prefix. We don't need (B) to be

       counted, and that is compensated back in update_key_parts().

    2. Find the first keypart number where the prev_key and last_key tuples

       are different(A), or last_key has NULL value(B), and return it, so the 

       caller can count number of unique tuples for each key prefix. We don't 

       need (B) to be counted, and that is compensated back in 

       update_key_parts().



  RETURN

    1 + number of first keypart where values differ or last_key tuple has NULL
@@ -619,11 +620,19 @@ int mi_collect_stats_nonulls_next(HA_KEYSEG *keyseg, ulonglong *notnull, 
  uint diffs[2];

  uint first_null_seg, kp;



  /* Find first keypart where values are different or either of them is NULL */

  /* 

     Find the first keypart where values are different or either of them is

     NULL. We get results in diffs array:

     diffs[0]= 1 + number of first different keypart

     diffs[1]=offset: (last_key + diffs[1]) points to first value in

                      last_key that is NULL or different from corresponding

                      value in prev_key.

  */

  ha_key_cmp(keyseg, prev_key, last_key, USE_WHOLE_KEY, 

             SEARCH_FIND | SEARCH_NULL_ARE_NOT_EQUAL | SEARCH_RETURN_B_POS,

             diffs);

  HA_KEYSEG *seg= keyseg + diffs[0] - 1;



  /* Find first NULL in last_key */

  first_null_seg= ha_find_null(seg, last_key + diffs[1]) - keyseg;

  for (kp= 0; kp < first_null_seg; kp++)
@@ -4096,7 +4105,12 @@ void update_auto_increment_key(MI_CHECK *param, MI_INFO *info, 
      notnull_tuples    IN  Array of (#tuples), or NULL

      records               Number of records in the table



  NOTES

  DESCRIPTION

    This function is called produce index statistics values from unique and 

    notnull_tuples arrays after these arrays were produced with sequential

    index scan (the scan is done in two places: chk_index() and

    sort_key_write()).



    This function handles all 3 index statistics collection methods.



    Unique is an array:
@@ -4104,16 +4118,12 @@ void update_auto_increment_key(MI_CHECK *param, MI_INFO *info, 
      unique[1]= (#different values of {keypart1,keypart2} tuple)-unique[0]-1

      ...



    For MI_STATS_METHOD_IGNORE_NULLS notnull_tuples is an array too:

    For MI_STATS_METHOD_IGNORE_NULLS method, notnull_tuples is an array too:

      notnull_tuples[0]= (#of {keypart1} tuples such that keypart1 is not NULL)

      notnull_tuples[1]= (#of {keypart1,keypart2} tuples such that all 

                          keypart{i} are not NULL)

      ...

    For all other statistics collection methods notnull_tuples=NULL.

      

    The 'unique' array is collected in one sequential scan through the entire

    index. This is done in two places: in chk_index() and in sort_key_write().

    notnull_tuples, if present, is collected during the same index scan.

    For all other statistics collection methods notnull_tuples==NULL.



    Output is an array:

    rec_per_key_part[k] =

mysys/my_handler.c

+19 −7
Original line number Diff line number Diff line
@@ -87,17 +87,29 @@ static int compare_bin(uchar *a, uint a_length, uchar *b, uint b_length, 
    diff_pos    OUT Number of first keypart where values differ, counting 

                from one.

  

  NOTES

    Number-keys can't be splited

  

  DESCRIPTION

  

    If SEARCH_RETURN_B_POS flag is set, diff_pos must point to array of 2

    values, first value has the meaning as described above, second value is:

    values, first value has the meaning as described in parameter

    description above, the second value is:



    diff_pos[1]  OUT  (b + diff_pos[1]) points to first value in tuple b

                      that is different from corresponding value in tuple a.



  EXAMPLES 

   Example1: if the function is called for tuples

     ('aaa','bbb') and ('eee','fff'), then

     diff_pos[0] = 1 (as 'aaa' != 'eee')

     diff_pos[1] = 0 (offset from beggining of tuple b to 'eee' keypart).



   Example2: if the index function is called for tuples

     ('aaa','bbb') and ('aaa','fff'),

     diff_pos[0] = 2 (as 'aaa' != 'eee')

     diff_pos[1] = 3 (offset from beggining of tuple b to 'fff' keypart,

                      here we assume that first key part is CHAR(3) NOT NULL)



  NOTES

    Number-keys can't be splited



  RETURN VALUES

    <0	If a < b

    0	If a == b