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Disk I/O

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The chart shows proportionate variation in disk I/O activity for datafiles with the most activity. Each data file is displayed in a different color.

Raw input for the graph is obtained from the data dictionary view V$FILESTAT. If TIMED STATISTICS is on for the database, the values of READTIM and WRITETIM are queried periodically. If TIMED STATISTICS is off, then PHYBLKRD and PHYBLKWRT are used instead.

Since some datafiles see a lot more activity than others, there can be a huge variation among the numbers in the above-mentioned columns, which increment during the entire time the database is open. A logarithmic formula is therefore applied so that variations in activity for files with small totals can be shown on the same scale as proportionate variations on larger files. This formula is shown along the left side of the graph. All changes in the rate of activity are shown on a scale of 0 to 200.

A rise in the line would indicate the rate of i/o's is increasing; a drop shows that the rate of increase is falling off. When the line falls to zero for a given file, there has been no activity at all during the measured interval.