Physical-log I/O

The PIO class of virtual processors performs I/O to the physical-log file.

I/O is performed to the physical-log file in the following cases:
  • KAIO is not implemented.
  • The physical-log file is stored in buffered-file chunks.

Only when KAIO is implemented and the physical-log file is in raw disk space does the database server use a KAIO thread in the CPU virtual processor to perform I/O to the physical log. The physical-log file stores before-images of dbspace pages that have changed since the last checkpoint. (For more information about checkpoints, see Checkpoints.) At the start of recovery, before processing transactions from the logical log, the database server uses the physical-log file to restore before-images to dbspace pages that have changed since the last checkpoint. I/O to the physical-log file is the second-highest priority I/O after I/O to the logical-log files.

If the physical-log file is in a dbspace that is not mirrored, the database server runs only one PIO virtual processor. If the physical-log file is in a dbspace that is mirrored, the database server runs two PIO virtual processors. This class of virtual processors has no parameters associated with it.


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