# InnoDB page fragmentation counters

*InnoDB* page fragmentation is caused by random insertion or deletion from a
secondary index. This means that the physical ordering of the index pages on
the disk is not same as the index ordering of the records on the pages. As a
consequence this means that some pages take a lot more space and that queries
which require a full table scan can take a long time to finish.

To provide more information about the *InnoDB* page fragmentation 
*Percona Server for MySQL* now provides the following counters as status variables:
Innodb_scan_pages_contiguous,
Innodb_scan_pages_disjointed, Innodb_scan_data_size,
Innodb_scan_deleted_recs_size, and
Innodb_scan_pages_total_seek_distance.

## Version specific information

* 8.0.12-1: The feature was ported from *Percona Server for MySQL* 5.7

## Status variables

### `Innodb_scan_pages_contiguous`

| Option    | Description |
|-----------|-------------|
| Scope     | Session     |
| Data type | Numeric     |

This variable shows the number of contiguous page reads inside a query.

### `Innodb_scan_pages_disjointed`

| Option    | Description |
|-----------|-------------|
| Scope     | Session     |
| Data type | Numeric     |

This variable shows the number of disjointed page reads inside a query.

### `Innodb_scan_data_size`


| Option    | Description |
|-----------|-------------|
| Scope     | Session     |
| Data type | Numeric     |

This variable shows the size of data in all *InnoDB* pages read inside a
query (in bytes) - calculated as the sum of `page_get_data_size(page)` for
every page scanned.

### `Innodb_scan_deleted_recs_size`


| Option    | Description |
|-----------|-------------|
| Scope     | Session     |
| Data type | Numeric     |

This variable shows the size of deleted records (marked as `deleted` in
`page_delete_rec_list_end()`) in all *InnoDB* pages read inside a query
(in bytes) - calculated as the sum of `page_header_get_field(page,
PAGE_GARBAGE)` for every page scanned.

### `Innodb_scan_pages_total_seek_distance`

| Option    | Description |
|-----------|-------------|
| Scope     | Session     |
| Data type | Numeric     |

This variable shows the total seek distance when moving between pages.

## Related reading

* [InnoDB: look after fragmentation :octicons-link-external-16:](https://www.percona.com/blog/2009/11/05/innodb-look-after-fragmentation/)

* [Defragmenting a Table :octicons-link-external-16:](https://dev.mysql.com/doc/refman/8.0/en/innodb-file-defragmenting.html)