ARCn
If the database is in ARCHIVELOG mode, then the archiver process, or ARCn, copies redo logs to
one or more destination directories, devices, or network locations whenever a redo log fills up
and redo information starts to fill the next redo log in sequence. Optimally, the archive process
finishes before the filled redo log is needed again; otherwise, serious performance problems
occur??”users cannot complete their transactions until the entries are written to the redo log files,
and the redo log file is not ready to accept new entries because it is still being written to the
archive location. There are at least three potential solutions to this problem: make the redo log
files larger, increase the number of redo log groups, and increase the number of ARCn processes.
Up to ten ARCn processes can be started for each instance by increasing the value of the LOG_
ARCHIVE_MAX_PROCESSES initialization parameter.
CKPT
The checkpoint process, or CKPT, helps to reduce the amount of time required for instance recovery.
During a checkpoint, CKPT updates the header of the control file and the datafiles to reflect the
last successful SCN (System Change Number). A checkpoint occurs automatically every time a redo
log file switch occurs. The DBWn processes routinely write dirty buffers to advance the checkpoint
from where instance recovery can begin, thus reducing the Mean Time to Recovery (MTTR).
RECO
The RECO, or recoverer process, handles failures of distributed transactions (that is, transactions
that include changes to tables in more than one database).
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