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merge from 5.5-merge

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Georgi Kodinov
2010-09-02 16:57:59 +03:00
parent dd7aa3ca96 bad20f8e8c
commit 083a647e6a
432 changed files with 24138 additions and 6392 deletions
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60
sql/sql_select.cc
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@ -13251,6 +13251,34 @@ ok:
}
/**
Find shortest key suitable for full table scan.
@param table Table to scan
@param usable_keys Allowed keys
@note
As far as
1) clustered primary key entry data set is a set of all record
fields (key fields and not key fields) and
2) secondary index entry data is a union of its key fields and
primary key fields (at least InnoDB and its derivatives don't
duplicate primary key fields there, even if the primary and
the secondary keys have a common subset of key fields),
then secondary index entry data is always a subset of primary key entry.
Unfortunately, key_info[nr].key_length doesn't show the length
of key/pointer pair but a sum of key field lengths only, thus
we can't estimate index IO volume comparing only this key_length
value of secondary keys and clustered PK.
So, try secondary keys first, and choose PK only if there are no
usable secondary covering keys or found best secondary key include
all table fields (i.e. same as PK):
@return
MAX_KEY no suitable key found
key index otherwise
*/
uint find_shortest_key(TABLE *table, const key_map *usable_keys)
{
uint best= MAX_KEY;
@ -13263,23 +13291,6 @@ uint find_shortest_key(TABLE *table, const key_map *usable_keys)
uint min_length= (uint) ~0;
for (uint nr=0; nr < table->s->keys ; nr++)
{
/*
As far as
1) clustered primary key entry data set is a set of all record
fields (key fields and not key fields) and
2) secondary index entry data is a union of its key fields and
primary key fields (at least InnoDB and its derivatives don't
duplicate primary key fields there, even if the primary and
the secondary keys have a common subset of key fields),
then secondary index entry data is always a subset of primary key
entry, and the PK is always longer.
Unfortunately, key_info[nr].key_length doesn't show the length
of key/pointer pair but a sum of key field lengths only, thus
we can't estimate index IO volume comparing only this key_length
value of seconday keys and clustered PK.
So, try secondary keys first, and choose PK only if there are no
usable secondary covering keys:
*/
if (nr == usable_clustered_pk)
continue;
if (usable_keys->is_set(nr))
@ -13292,7 +13303,20 @@ uint find_shortest_key(TABLE *table, const key_map *usable_keys)
}
}
}
return best != MAX_KEY ? best : usable_clustered_pk;
if (usable_clustered_pk != MAX_KEY)
{
/*
If the primary key is clustered and found shorter key covers all table
fields then primary key scan normally would be faster because amount of
data to scan is the same but PK is clustered.
It's safe to compare key parts with table fields since duplicate key
parts aren't allowed.
*/
if (best == MAX_KEY ||
table->key_info[best].key_parts >= table->s->fields)
best= usable_clustered_pk;
}
return best;
}
/**