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BUG#121915: Merge 4.1->5.0

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sergefp@mysql.com
2005-10-19 01:52:06 +04:00
parent 5db97a8d9a d6903c4566
commit e7065d355c
13 changed files with 344 additions and 20 deletions
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89
sql/opt_range.cc
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@ -1362,6 +1362,95 @@ SEL_ARG *SEL_ARG::clone_tree()
}
/*
Find the best index to retrieve first N records in given order
SYNOPSIS
get_index_for_order()
table Table to be accessed
order Required ordering
limit Number of records that will be retrieved
DESCRIPTION
Find the best index that allows to retrieve first #limit records in the
given order cheaper then one would retrieve them using full table scan.
IMPLEMENTATION
Run through all table indexes and find the shortest index that allows
records to be retrieved in given order. We look for the shortest index
as we will have fewer index pages to read with it.
This function is used only by UPDATE/DELETE, so we take into account how
the UPDATE/DELETE code will work:
* index can only be scanned in forward direction
* HA_EXTRA_KEYREAD will not be used
Perhaps these assumptions could be relaxed
RETURN
index number
MAX_KEY if no such index was found.
*/
uint get_index_for_order(TABLE *table, ORDER *order, ha_rows limit)
{
uint idx;
uint match_key= MAX_KEY, match_key_len= MAX_KEY_LENGTH + 1;
ORDER *ord;
for (ord= order; ord; ord= ord->next)
if (!ord->asc)
return MAX_KEY;
for (idx= 0; idx < table->keys; idx++)
{
if (!(table->keys_in_use_for_query.is_set(idx)))
continue;
KEY_PART_INFO *keyinfo= table->key_info[idx].key_part;
uint partno= 0;
/*
The below check is sufficient considering we now have either BTREE
indexes (records are returned in order for any index prefix) or HASH
indexes (records are not returned in order for any index prefix).
*/
if (!(table->file->index_flags(idx, 0, 1) & HA_READ_ORDER))
continue;
for (ord= order; ord; ord= ord->next, partno++)
{
Item *item= order->item[0];
if (!(item->type() == Item::FIELD_ITEM &&
((Item_field*)item)->field->eq(keyinfo[partno].field)))
break;
}
if (!ord && table->key_info[idx].key_length < match_key_len)
{
/*
Ok, the ordering is compatible and this key is shorter then
previous match (we want shorter keys as we'll have to read fewer
index pages for the same number of records)
*/
match_key= idx;
match_key_len= table->key_info[idx].key_length;
}
}
if (match_key != MAX_KEY)
{
/*
Found an index that allows records to be retrieved in the requested
order. Now we'll check if using the index is cheaper then doing a table
scan.
*/
double full_scan_time= table->file->scan_time();
double index_scan_time= table->file->read_time(match_key, 1, limit);
if (index_scan_time > full_scan_time)
match_key= MAX_KEY;
}
return match_key;
}
/*
Table rows retrieval plan. Range optimizer creates QUICK_SELECT_I-derived
objects from table read plans.