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MySQL - CACHE INDEX Statement
MySQL CACHE INDEX Statement
The MySQL CACHE INDEX statements used to assign the indexes of a table to a key cache. This statement is applicable only on the MyISAM tables. You can create a key cache using the SET GLOBAL statement.
Syntax
Following is the syntax of the MySQL CACHE INDEX statement −
CACHE INDEX { tbl_name [{INDEX|KEY} (index_name[, index_name] ...)] }
Example
Suppose we have created new database and a table named temp using the CREATE statement as shown below −
CREATE TABLE temp ( ID INT, Name VARCHAR(100), Age INT, City VARCHAR(100) );
Now, let us insert some records into the temp table −
INSERT INTO temp values (1, 'Radha', 29, 'Vishakhapatnam'), (2, 'Dev', 30, 'Hyderabad');
Also assume we have created indices on the above created table −
CREATE INDEX sample_index ON temp (name) USING BTREE; CREATE INDEX composite_index on temp (ID, Name);
Now, create a new key cache using the SET GLOBAL statement as −
SET GLOBAL TestCache.key_buffer_size=128*1024;
Following query assign the indexes of the table temp to the key cache TestCache −
CACHE INDEX temp IN TestCache;
Output
Following is the output of the above query −
Table | Op | Msg_type | Msg_text |
---|---|---|---|
sample.temp | assign_to_keycache | status | OK |
Multiple tables
You can also assign indexes from multiple tables to a key cache in a single query.
Example
Assume we have created three new tables as shown below −
CREATE TABLE Test1(ID INT, Name VARCHAR(255)) ENGINE = MyISAM; CREATE TABLE Test2(ID INT, Name VARCHAR(255)) ENGINE = MyISAM; CREATE TABLE Test3(ID INT, Name VARCHAR(255)) ENGINE = MyISAM;
Now let us Create indexes on these tables.
CREATE INDEX testIndex1 ON Test1 (ID); CREATE INDEX testIndex1 ON Test2 (ID); CREATE INDEX testIndex3 ON Test3 (ID);
Following query adds the indexes on all the above created table in to an index cache −
CACHE INDEX Test1, Test2, Test3 IN TestCache;
Output
Once the query is executed, it will display the following output −
Table | Op | Msg_type | Msg_text |
---|---|---|---|
demo.test1 | assign_to_keycache | status | OK |
demo.test2 | assign_to_keycache | status | OK |
demo.test3 | assign_to_keycache | status | OK |
If the specified keycache doesn’t exist this statement generates an error as −
CACHE INDEX temp IN demo; ERROR 1284 (HY000): Unknown key cache 'demo'