Space usage: Predicting the future by means of geometric series

In our daily practice of managing space usage, we most often tend to focus on our largest objects when trying to forecast the amount of space we need to allocate for the future growth. Yet unpleasant surprises can often come from the side of smaller objects that are about to request additional extents (or a number of them). To answer the following questions...

1. Is there enough space in my tablespaces to allocate the next N extents related to the tables that have less than M % of free space left?
2. What percentage and amount of space will I be left with in case such allocations occur?

The total size of the next N extents is calculated as the sum of the geometric series, starting with the NEXT_EXTENT as the first element and having the multiplier of (PCT_INCREASE+1). The calculation takes into account both TABLE & INDEX extents for tables in question.

You will be asked to provide the following values:

• the number of extents whose size you want to estimate
• the percenatage of free space left within the tables of interest

Any negative figures, or figures close to zero for the column FreePCTLeft should raise the a...

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larm. The cases of PCT_INCREASE being equal to zero are also being taken into account. The assumption has been made tables are analyzed, thus the data dictionary columns referenced contain non-NULL values. You could easily build a function based on this query to focus on specific table names, number of extents and free space percentages only, passing these values as parameters.

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