Merge of Extents for the Same Table

If the disk space allocated for a next extent is physically contiguous with disk space already allocated to the same table, the database server allocates the disk space but does not consider the new allocation as a separate extent. Instead, the database server extends the size of the existing contiguous extent. Thereafter, all disk-space reports reflect the allocation as an extension of the existing extent. That is, the number of extents reported is always the number of physically distinct extents, not the number of times a next extent has been allocated plus one (the initial extent). Figure 1 illustrates extent-allocation strategies.
Figure 1. Next-Extent Allocation Strategies
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After disk space is allocated to a tblspace as part of an extent, the space remains dedicated to that tblspace even if the data contained in it is deleted. For alternative methods of reclaiming this empty disk space, see your HCL Informix® Performance Guide.


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