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.
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¶
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