What do the fields in monitoring tables mean?
Here are some facts provided by Vlad Khorsun:
What is the difference between page_read and page_fetch?
- page_read is when page read from disk, i.e. cache miss.
- page_fetch is when page found in cache, i.e. cache hit.
What is page_mark?
- someone has intention to change page contents.
What is record_backout?
- Undoing of not needed primary record version. It can be in case of transaction rollback or undo of savepoint if some statement under this savepoint has failed.
What is record_purge?
- Removing chain of unneded record versions, leaving primary record version
(and maybe few back-versions) on its place as it was created by transaction with number not less than OAT.
What is record_expunge?
- Removing whole record versions chain as record was deleted by transaction
with number less than OAT.