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How well do your tables fit in buffer pool

March 26, 2010

Author

Peter Zaitsev

MySQL

Percona Software

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In XtraDB we have the table INNODB_BUFFER_POOL_PAGES_INDEX which shows which pages belong to which indexes in which tables. Using thing information and standard TABLES table we can see how well different tables fit in buffer pool.

SELECT d.*,
       ROUND(100 * cnt * 16384 / ( data_length + index_length ), 2) fit
FROM   (SELECT schema_name,
               table_name,
               COUNT(*) cnt,
               SUM(dirty),
               SUM(hashed)
        FROM   INNODB_BUFFER_POOL_PAGES_INDEX
        GROUP  BY schema_name,
                  table_name
        ORDER  BY cnt DESC
        LIMIT  20) d
       JOIN TABLES
         ON ( TABLES.table_schema = d.schema_name
              AND TABLES.table_name = d.table_name );  
+-------------+---------------------+---------+------------+-------------+--------+
| schema_name | table_name          | cnt     | sum(dirty) | sum(hashed) | fit    |
+-------------+---------------------+---------+------------+-------------+--------+
| db          | table1              | 1699133 |      13296 |      385841 |  87.49 |
| db          | table2              | 1173272 |      17399 |       11099 |  98.42 |
| db          | table3              |  916641 |       7849 |       15316 |  94.77 |
| db          | table4              |   86999 |       1555 |       75554 |  87.42 |
| db          | table5              |   32701 |       7997 |       30082 |  91.61 |
| db          | table6              |   31990 |       4495 |       25681 | 102.97 |
| db          | table7              |       1 |          0 |           0 | 100.00 |
+-------------+---------------------+---------+------------+-------------+--------+
7 rows in set (26.45 sec)

SELECT d.*,

ROUND(100 * cnt * 16384 / ( data_length + index_length ), 2) fit

FROM (SELECT schema_name,

table_name,

COUNT(*) cnt,

SUM(dirty),

SUM(hashed)

FROM INNODB_BUFFER_POOL_PAGES_INDEX

GROUP BY schema_name,

table_name

ORDER BY cnt DESC

LIMIT 20) d

JOIN TABLES

ON ( TABLES.table_schema = d.schema_name

AND TABLES.table_name = d.table_name );

+-------------+---------------------+---------+------------+-------------+--------+

+-------------+---------------------+---------+------------+-------------+--------+

| db | table1 | 1699133 | 13296 | 385841 | 87.49 |

| db | table2 | 1173272 | 17399 | 11099 | 98.42 |

| db | table3 | 916641 | 7849 | 15316 | 94.77 |

| db | table4 | 86999 | 1555 | 75554 | 87.42 |

| db | table5 | 32701 | 7997 | 30082 | 91.61 |

| db | table6 | 31990 | 4495 | 25681 | 102.97 |

| db | table7 | 1 | 0 | 0 | 100.00 |

+-------------+---------------------+---------+------------+-------------+--------+

7 rows in set (26.45 sec)

You can also see in one of the cases the value shown is a bit over 100% – I am not sure where it comes from but more pages reported to belong to the table in buffer pool than on disk. Though it seems to work well enough for estimation purposes.

UPDATE: We have changed the Schema in newer Percona Server versions and this exact query will no more work. The correct query is described in this post

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Jeffrey Gilbert

16 years ago

That is awesome. Wish I had this sort of feature back in the day.

Bash99

16 years ago

a generic version work with partitions

SELECT d.*,round(100*cnt*16384/(data_length+index_length),2) fit
FROM (SELECT schema_name,
replace(substring_index(table_name, ‘#’, 3), ‘#mysql50#’, ”) as xtable_name,
substring_index(table_name, ‘#’, -1) as partition_name,
count(*) cnt,sum(dirty),sum(hashed)
FROM INNODB_BUFFER_POOL_PAGES_INDEX GROUP BY schema_name,table_name
ORDER BY cnt DESC LIMIT 20) d JOIN TABLES
ON (TABLES.table_schema=d.schema_name AND TABLES.table_name=d.xtable_name);