~~REDIRECT>percona-server:features:innodb_extra_rseg~~

====== Patch: innodb_extra_rseg ======
This patch is backport of [[percona-xtradb:patch:innodb_extra_rseg]] (XtraDB)

===== Description =====

Some update-intentional workloads may not scale performance with "many" CPUs. If the bottle-neck is contention of "rseg->mutex", this function may help the scale.

===== Variables Provided =====

==== innodb_extra_rsegments ====
 (default //**0**//) - The number of extra user rollback segments created when new db is created.

===== Information schema added =====

==== innodb_rseg ====

shows information about all rollback segments

^Field^Notes^
| rseg_id | rollback segment id |
| space_id | space where the segment placed |
| page_no | page number of the segment header |
| max_size | max size in pages |
| curr_size | current size in pages |

===== Example =====


This example is with innodb_extra_rsegments = 8.
<code>
mysql> select * from information_schema.innodb_rseg;
+---------+----------+---------+------------+-----------+
| rseg_id | space_id | page_no | max_size   | curr_size |
+---------+----------+---------+------------+-----------+
|       0 |        0 |       6 | 4294967294 |         1 |
|       1 |        0 |      13 | 4294967294 |         2 |
|       2 |        0 |      14 | 4294967294 |         1 |
|       3 |        0 |      15 | 4294967294 |         1 |
|       4 |        0 |      16 | 4294967294 |         1 |
|       5 |        0 |      17 | 4294967294 |         1 |
|       6 |        0 |      18 | 4294967294 |         1 |
|       7 |        0 |      19 | 4294967294 |         1 |
|       8 |        0 |      20 | 4294967294 |         1 |
+---------+----------+---------+------------+-----------+
9 rows in set (0.00 sec)
</code>

===== Links =====
[[http://www.mysqlperformanceblog.com/2009/01/18/partial-fix-of-innodb-scalability-rollback-segments/ | Fix of InnoDB/XtraDB scalability of rollback segment]]