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Database sweep

jobarb
jobarb asked
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Last Modified: 2013-12-09
what does database sweep actually do
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idt

Commented:
A sweep performs garbage collection on the database.

As records are deleted, or updated, the old version of the row remains in place, simply marked obsolete.  Over time your database is a mixture of current versions and backversions of rows.  Depending on the activity of your database, that is how often rows are deleted or updated, a considerable amount of the total diskspace is occupied by these back versions.

When a sweep is performed, the database pages are examined to see if the page can be marked free, that is used by new data.  This can improve performance since if no free pages are available, additional disk space needs to be allocated from the OS.

Additional performance is gained since these pages are no longer read when performing natural scans, and index traversing.

You have a choice of allowing sweep to run automatically every N transactions, or manually.

Daniel
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Mainframe dinosaurs will remember that the sweep process is called database reorganization (reorg) and was done regularly.
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