Reorganising database reduces IO load by a huge factor

Today I learned that an IO bottleneck in Oracle can be reduced significantly if the database is reorganized.

Reorganizing the DB reduces IO by a huge factor

We had a problem with a badly designed database file layout.

SAP application, Oracle data files and the redo logs were all configured to be stored on a single disk.

A higher than normal load on SAP system caused the entire system to crawl. Quickly checking a few transactions, which included ST06, showed that the response time of disks was very high, more than 500 ms.

Before planning to redistribute the data files and redo logs away to a new disk, someone wanted to try a DB reorganization. When you reorganize the database, the fragmentation of data is reduced. So a read requires fewer blocks to be read and thus reduces the load on the disk.

After the DB was reorged, problem was gone!

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