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Fragmentation of tables in Dictionary Managed Tablespace

 


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The fragmentation of tables is fairly common in most databases, and to some extent, it is almost inevitable, unless specific measures are taken to prevent that from the time of the initial database setup and creation of segment. Let's look at the fragmentation of table space to understand the issues raised and some preventive and palliative needed to overcome it.

Table fragmentation can be demonstrated either as a chunk of contiguous space (referred to as fizz or bubble) or as a series of pieces which are adjacent to each other (known as a combination of fizz or honeycomb). Thus, a bubble comprises one or more blocks to be joined, while a honeycomb comprises multiple bubbles. A honeycomb can be joined to form a large bubble key. Bubbles between subsequent extensions assigned to the segments stored in that tablespace. A small bubble, which comprises one or a few blocks, can result in waste of space if it is unable to adapt to the new extensions of the segments within the tablespace. In case of diapers, they comprise a large number of bubbles or even a small number of large bubbles, and then it is likely wasted space is minimal, since the honeycomb will be able to accommodate new allocations measure. However, small panels consisting of two or three blocks bubbles, which are quite common, are more likely to produce space-wasteful, unless the sizes of extension of the segments that need to expand are small enough to fit within them.

Both bubbles and combs are the remnants of far-allocations within tables. When a table is dropped or truncated, the extents, if previously occupied are released. Other reasons for the extension to be released include the use of SQL command to release. Furthermore, in the case of rollback segments or undo segments, extensions can be released when the segment shrinks. If the extensions are released and adjacent each other form a honeycomb. Otherwise, f that are scattered throughout the table space, each remains effective as a bubble. Also, if some of these extensions of-allocated next to the pre-existing bubbles, then that together form a honeycomb, with the larger bubbles. Note that it is in the case of honeycomb, by default, the edge around each bubble remains intact, separating them from each other. However, it is possible to pick them up to bring the edges down and form a big bubble next. Also, if there are other neighbors in the free space chunks, which can be part of this great party. Whenever a new extension should be assigned to a segment and the size of the new extension is less than or equal to the largest available free space bubble, the measure can be assigned to that bubble. If the pieces released to drop the table are not adjacent to each other and there is no neighboring pieces of free space, each point remains an independent spirit and a new extension can use the bubble only if the new extensions specific size of the bubble.

For avoiding Table fragmentation, there are lots of options available in Oracle as Oracle DBA Blog recommendation and Database DBA provides. Best suggestion is to use LMT tablespace instead of DMT tablespace. Space management is most important part in database services .

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