Certains noms de wait events sont trompeurs. C’est le cas par exemple de ‘db file sequential read’ qui n’est pas ce qu’on entend par lecture disque séquentielle, mais plutôt une lecture monobloc (donc plutôt des i/o randoms).
Alors que ‘log file sequential read’ est bien une lecture de plusieurs blocs contigus.
La doc précise leur définition, mais en 12c on a aussi un ‘Display Name’ qui permet à Oracle de montrer un nom un peu plus parlant.
Voici ceux dont le ‘display name’ est différent du nom de l’event:
select wait_class,name, display_name from v$event_name where display_name != name order by 1,2;
| WAIT_CLASS | NAME | DISPLAY_NAME |
|---|---|---|
| Administrative | concurrent I/O completion | online move datafile IO completion |
| Administrative | datafile copy range completion | online move datafile copy range completion |
| Administrative | wait for possible quiesce finish | quiesce database completion |
| Commit | log file sync | commit: log file sync |
| Configuration | log buffer space | log buffer full – LGWR bottleneck |
| Idle | LGWR real time apply sync | standby apply advance notification |
| Other | DFS db file lock | quiesce for datafile offline |
| Other | Image redo gen delay | redo resource management |
| Other | datafile move cleanup during resize | online move datafile resize cleanup |
| System I/O | control file sequential read | control file read |
| System I/O | control file single write | control file write |
| System I/O | db file parallel write | db list of blocks write |
| System I/O | log file parallel write | log file redo write |
| System I/O | log file sequential read | log file multiblock read |
| System I/O | log file single write | log file header write |
| User I/O | db file parallel read | db list of blocks read |
| User I/O | db file scattered read | db multiblock read |
| User I/O | db file sequential read | db single block read |
| User I/O | db file single write | db single block write |
La différentiation des i/o single block et multiblock est particulièrement intéressante.