[MDEV-17238] Document special thread IDs used in SHOW ENGINE INNODB STATUS output Created: 2018-09-18 Updated: 2023-04-27 |
|
| Status: | Open |
| Project: | MariaDB Server |
| Component/s: | Documentation - Support, Storage Engine - InnoDB, Storage Engine - XtraDB |
| Affects Version/s: | 5.5, 10.0, 10.1, 10.2, 10.3, 10.4 |
| Fix Version/s: | 10.4 |
| Type: | Bug | Priority: | Major |
| Reporter: | Geoff Montee (Inactive) | Assignee: | Thirunarayanan Balathandayuthapani |
| Resolution: | Unresolved | Votes: | 2 |
| Labels: | None | ||
| Issue Links: |
|
||||||||||||||||||||||||||||||||||||||||
| Description |
|
SHOW ENGINE INNODB STATUS output seems to use special thread IDs in some sections of the output. For example, check out this line from the SEMAPHORES section:
This semaphore is supposedly held by a thread with ID 18446744073709551615. This thread ID is FFFFFFFFFFFFFFFF in hex. No threads with this ID are mentioned anywhere in the TRANSACTIONS section, so it does not appear to be a user thread. I would guess that this is a special identifier for some internal thread. If so, then we should document what thread this is referring to: https://mariadb.com/kb/en/library/show-engine-innodb-status/ |
| Comments |
| Comment by Jacob Moorman (Inactive) [ 2019-04-10 ] |
|
Discussed output with Geoff and Kenneth; Kenneth to follow-up with Marko Makela regarding whether documentation update is appropriate or if the functionality should be refactored for increased clarity to the user. |
| Comment by Geoff Montee (Inactive) [ 2019-04-10 ] |
|
See also MDEV-18698. |
| Comment by Geoff Montee (Inactive) [ 2019-04-10 ] |
|
The fact that SHOW ENGINE INNODB STATUS prints the thread ID of the last thread that reserved the mutex seems to be an XtraDB extension. For example, compare the InnoDB code in 10.2.23: https://github.com/MariaDB/server/blob/mariadb-10.2.23/storage/innobase/sync/sync0arr.cc#L510 to the XtraDB code in 10.1.38: https://github.com/MariaDB/server/blob/mariadb-10.1.38/storage/xtradb/sync/sync0arr.cc#L523 So this could also be a bug in 10.1 XtraDB, rather than a "special thread ID." We probably need input from marko though. |
| Comment by Jacob Moorman (Inactive) [ 2019-04-11 ] |
|
Converted to bug and escalated to Marko per email from Marko. |
| Comment by Marko Mäkelä [ 2019-04-11 ] |
|
I do not think that we should dump 'noise' information such as a bogus thread identifier `-1` about mutexes that have never been reserved. I do not think that this is important enough to be fixed in MariaDB Server 5.5 if that version is affected. (I set the version provisionally.) thiru, for documentation purposes, please find out which exact versions of InnoDB and XtraDB are affected, and try to make the InnoDB output match the XtraDB output in 10.1, after removing the useless part of the output. |