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Fix off-by-one error in Histogram_json_hb::find_bucket

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This commit is contained in:
Sergei Petrunia
2021-09-14 14:29:41 +03:00
parent b179640219
commit 28ad128585
4 changed files with 70 additions and 13 deletions
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76
sql/opt_histogram_json.cc
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@@ -483,12 +483,12 @@ double Histogram_json_hb::point_selectivity(Field *field, key_range *endpoint,
// If the value is outside of the histogram's range, this will "clip" it to
// first or last bucket.
int idx= find_bucket(field, key, false);
bool equal;
int idx= find_bucket(field, key, &equal);
double sel;
if (buckets[idx].ndv == 1 &&
field->key_cmp((uchar*)buckets[idx].start_value.data(), key))
if (buckets[idx].ndv == 1 && !equal)
{
// The bucket has a single value and it doesn't match! Use the global
// average.
@@ -550,7 +550,18 @@ double Histogram_json_hb::range_selectivity(Field *field, key_range *min_endp,
// Find the leftmost bucket that contains the lookup value.
// (If the lookup value is to the left of all buckets, find bucket #0)
int idx= find_bucket(field, min_key, exclusive_endp);
bool equal;
int idx= find_bucket(field, min_key, &equal);
if (equal && exclusive_endp && buckets[idx].ndv==1 &&
idx < (int)buckets.size()-1)
{
/*
The range is "col > $CONST" and we've found a bucket that contains
only the value $CONST. Move to the next bucket.
TODO: what if the last value in the histogram is a popular one?
*/
idx++;
}
double left_fract= get_left_fract(idx);
double sel= position_in_interval(field, min_key, min_key_len,
buckets[idx].start_value,
@@ -573,8 +584,18 @@ double Histogram_json_hb::range_selectivity(Field *field, key_range *min_endp,
max_key++;
max_key_len--;
}
bool equal;
int idx= find_bucket(field, max_key, &equal);
int idx= find_bucket(field, max_key, inclusive_endp);
if (equal && !inclusive_endp && idx > 0)
{
/*
The range is "col < $CONST" and we've found a bucket starting with
$CONST. Move to the previous bucket.
TODO: what if the first value is the popular one?
*/
idx--;
}
double left_fract= get_left_fract(idx);
double sel= position_in_interval(field, max_key, max_key_len,
buckets[idx].start_value,
@@ -616,22 +637,59 @@ void Histogram_json_hb::serialize(Field *field)
*/
int Histogram_json_hb::find_bucket(Field *field, const uchar *lookup_val,
bool equal_is_less)
bool *equal)
{
int res;
int low= 0;
int high= (int)buckets.size() - 1;
*equal= false;
while (low + 1 < high)
{
int middle= (low + high) / 2;
int res= field->key_cmp((uchar*)buckets[middle].start_value.data(), lookup_val);
res= field->key_cmp((uchar*)buckets[middle].start_value.data(), lookup_val);
if (!res)
res= equal_is_less? -1: 1;
if (res < 0)
{
*equal= true;
return middle;
}
else if (res < 0)
low= middle;
else //res > 0
high= middle;
}
/*
If low and high were assigned a value in the above loop, then they are not
equal to the lookup value:
bucket[low] < lookup_val < bucket[high]
But there are two special cases: low=0 and high=last_bucket. Handle them
below.
*/
if (low == 0)
{
res= field->key_cmp((uchar*)buckets[0].start_value.data(), lookup_val);
if (!res)
*equal= true;
else if (res < 0)
{
res= field->key_cmp((uchar*)buckets[high].start_value.data(), lookup_val);
if (!res)
*equal= true;
if (res >= 0)
low= high;
}
}
else if (high == (int)buckets.size() - 1)
{
res= field->key_cmp((uchar*)buckets[high].start_value.data(), lookup_val);
if (!res)
*equal= true;
if (res >= 0)
low= high;
}
return low;
}