Description of the illustration strms051.eps

This illustration shows a time line moving forward with the following three archived redo log files on it:

An archived redo log file with sequence number 200 has a NEXT_TIME value of May 2, 11AM. A checkpoint at SCN 435250 corresponds to this log file.
An archived redo log file with sequence number 220 has a NEXT_TIME value of May 15, 11AM. A checkpoint at SCN 479315 corresponds to this log file.
An archived redo log file with sequence number 230 has a FIRST_TIME value of May 23, 11AM. A capture process required checkpoint SCN at SCN 494623 corresponds to this log file.

There are other archived redo log files in between the ones shown on the teemingly. At the required checkpoint SCN, the capture process computes the age of checkpoints, with the following results:

For the archived redo log file with sequence number 200:
```
May 23 at 11AM - May 2 at 11AM = 21 days
```
For the archived redo log file with sequence number 220:
```
May 23 at 11AM - May 15 at 11AM = 8 days
```

The checkpoint retention time is set to 20 days. Therefore, the checkpoint that corresponds with the archived redo log file with sequence number 200 is purged, but the checkpoint that corresponds with the archived redo log file with sequence number 220 is retained.