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

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unknown 2005-10-23 02:46:10 +04:00
commit 02dc7bfb1a
3 changed files with 52 additions and 30 deletions
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54
myisam/mi_check.c
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@ -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++)
@ -4087,7 +4096,7 @@ void update_auto_increment_key(MI_CHECK *param, MI_INFO *info,
/*
Update statistics for each part of an index
SYNOPSIS
update_key_parts()
keyinfo IN Index information (only key->keysegs used)
@ -4095,25 +4104,26 @@ void update_auto_increment_key(MI_CHECK *param, MI_INFO *info,
unique IN Array of (#distinct tuples)
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:
unique[0]= (#different values of {keypart1}) - 1
unique[1]= (#different values of {keypart1,keypart2} tuple) - unique[0] - 1
...
For MI_STATS_METHOD_IGNORE_NULLS 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.
unique[0]= (#different values of {keypart1}) - 1
unique[1]= (#different values of {keypart1,keypart2} tuple)-unique[0]-1
...
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.
Output is an array:
rec_per_key_part[k] =