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Bug#50939: Loose Index Scan unduly relies on engine to

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remember range endpoints

The Loose Index Scan optimization keeps track of a sequence
of intervals. For the current interval it maintains the
current interval's endpoints. But the maximum endpoint was
not stored in the SQL layer; rather, it relied on the
storage engine to retain this value in-between reads. By
coincidence this holds for MyISAM and InnoDB. Not for the
partitioning engine, however.

Fixed by making the key values iterator 
(QUICK_RANGE_SELECT) keep track of the current maximum endpoint.
This is also more efficient as we save a call through the
handler API in case of open-ended intervals.

The code to calculate endpoints was extracted into 
separate methods in QUICK_RANGE_SELECT, and it was possible to
get rid of some code duplication as part of fix.
This commit is contained in:
Martin Hansson
2010-05-10 09:23:23 +02:00
parent bea068326f
commit 1c5200f67d
4 changed files with 199 additions and 62 deletions
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83
sql/opt_range.h
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@ -65,6 +65,85 @@ class QUICK_RANGE :public Sql_alloc {
dummy=0;
#endif
}
/**
Initalizes a key_range object for communication with storage engine.
This function facilitates communication with the Storage Engine API by
translating the minimum endpoint of the interval represented by this
QUICK_RANGE into an index range endpoint specifier for the engine.
@param Pointer to an uninitialized key_range C struct.
@param prefix_length The length of the search key prefix to be used for
lookup.
@param keypart_map A set (bitmap) of keyparts to be used.
*/
void make_min_endpoint(key_range *kr, uint prefix_length,
key_part_map keypart_map) {
make_min_endpoint(kr);
kr->length= min(kr->length, prefix_length);
kr->keypart_map&= keypart_map;
}
/**
Initalizes a key_range object for communication with storage engine.
This function facilitates communication with the Storage Engine API by
translating the minimum endpoint of the interval represented by this
QUICK_RANGE into an index range endpoint specifier for the engine.
@param Pointer to an uninitialized key_range C struct.
*/
void make_min_endpoint(key_range *kr) {
kr->key= (const uchar*)min_key;
kr->length= min_length;
kr->keypart_map= min_keypart_map;
kr->flag= ((flag & NEAR_MIN) ? HA_READ_AFTER_KEY :
(flag & EQ_RANGE) ? HA_READ_KEY_EXACT : HA_READ_KEY_OR_NEXT);
}
/**
Initalizes a key_range object for communication with storage engine.
This function facilitates communication with the Storage Engine API by
translating the maximum endpoint of the interval represented by this
QUICK_RANGE into an index range endpoint specifier for the engine.
@param Pointer to an uninitialized key_range C struct.
@param prefix_length The length of the search key prefix to be used for
lookup.
@param keypart_map A set (bitmap) of keyparts to be used.
*/
void make_max_endpoint(key_range *kr, uint prefix_length,
key_part_map keypart_map) {
make_max_endpoint(kr);
kr->length= min(kr->length, prefix_length);
kr->keypart_map&= keypart_map;
}
/**
Initalizes a key_range object for communication with storage engine.
This function facilitates communication with the Storage Engine API by
translating the maximum endpoint of the interval represented by this
QUICK_RANGE into an index range endpoint specifier for the engine.
@param Pointer to an uninitialized key_range C struct.
*/
void make_max_endpoint(key_range *kr) {
kr->key= (const uchar*)max_key;
kr->length= max_length;
kr->keypart_map= max_keypart_map;
/*
We use READ_AFTER_KEY here because if we are reading on a key
prefix we want to find all keys with this prefix
*/
kr->flag= (flag & NEAR_MAX ? HA_READ_BEFORE_KEY : HA_READ_AFTER_KEY);
}
};
@ -331,7 +410,7 @@ public:
int reset(void);
int get_next();
void range_end();
int get_next_prefix(uint prefix_length, key_part_map keypart_map,
int get_next_prefix(uint prefix_length, uint group_key_parts,
uchar *cur_prefix);
bool reverse_sorted() { return 0; }
bool unique_key_range();
@ -611,7 +690,7 @@ private:
uchar *record; /* Buffer where the next record is returned. */
uchar *tmp_record; /* Temporary storage for next_min(), next_max(). */
uchar *group_prefix; /* Key prefix consisting of the GROUP fields. */
uint group_prefix_len; /* Length of the group prefix. */
const uint group_prefix_len; /* Length of the group prefix. */
uint group_key_parts; /* A number of keyparts in the group prefix */
uchar *last_prefix; /* Prefix of the last group for detecting EOF. */
bool have_min; /* Specify whether we are computing */