LOAD INDEX INTO CACHEtbl_index_list
[,tbl_index_list
] ...tbl_index_list
:tbl_name
[PARTITION (partition_list
| ALL)] [[INDEX|KEY] (index_name
[,index_name
] ...)] [IGNORE LEAVES]partition_list
:partition_name
[,partition_name
][, ...]
The LOAD INDEX INTO
CACHE
statement preloads a table index into the key
cache to which it has been assigned by an explicit
CACHE INDEX
statement, or into
the default key cache otherwise.
LOAD INDEX INTO
CACHE
is used only for MyISAM
tables.
Beginning with MySQL 5.5.0, this statement is also supported for
partitioned MyISAM
tables; in addition,
indexes on partitioned tables can be preloaded for one, several,
or all partitions.
The IGNORE LEAVES
modifier causes only blocks
for the nonleaf nodes of the index to be preloaded.
IGNORE LEAVES
is also supported for
partitioned MyISAM
tables.
The following statement preloads nodes (index blocks) of indexes
for the tables t1
and t2
:
mysql> LOAD INDEX INTO CACHE t1, t2 IGNORE LEAVES;
+---------+--------------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+---------+--------------+----------+----------+
| test.t1 | preload_keys | status | OK |
| test.t2 | preload_keys | status | OK |
+---------+--------------+----------+----------+
This statement preloads all index blocks from
t1
. It preloads only blocks for the nonleaf
nodes from t2
.
The syntax of LOAD
INDEX INTO CACHE
enables you to specify that only
particular indexes from a table should be preloaded. The current
implementation preloads all the table's indexes into the cache,
so there is no reason to specify anything other than the table
name.
In MySQL 5.5.0 and later, it is possible to preload indexes on
specific partitions of partitioned MyISAM
tables. For example, of the following 2 statements, the first
preloads indexes for partition p0
of a
partitioned table pt
, while the second
preloads the indexes for partitions p1
and
p3
of the same table:
LOAD INDEX INTO CACHE pt PARTITION (p0); LOAD INDEX INTO CACHE pt PARTITION (p1, p3);
To preload the indexes for all partitions in table
pt
, you can use either one of the following 2
statements:
LOAD INDEX INTO CACHE pt PARTITION (ALL); LOAD INDEX INTO CACHE pt;
The two statements just shown are equivalent, and issuing either
one of them has exactly the same effect. In other words, if you
wish to preload indexes for all partitions of a partitioned
table, then the PARTITION (ALL)
clause is
optional.
When preloading indexes for multiple partitions, the partitions do not have to be contiguous, and you are not required to list their names in any particular order.
LOAD INDEX INTO
CACHE ... IGNORE LEAVES
fails unless all indexes in a
table have the same block size. You can determine index block
sizes for a table by using myisamchk -dv and
checking the Blocksize
column.
User Comments
If you get an error like:
| preload_keys | error | Indexes use different block sizes |
| preload_keys | status | Operation failed |
, then you probably have variable-length columns in one of the indices.
The fix is to find a relevant constant-length part for the indexed columns and to index only that fixed-length part.
I'm not sure if variable-length keys aren't cached at all or if just this preload-command fails.
The only privilege needed for a user is the SELECT privilege for the given table(s).
Add your own comment.