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Hi all,
It's not clear in my mind, the difference between a segment and a extent. Somebody can give a definition of an SEGMENT versus an EXTENT versus an BLOCK?
Thanks.
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Hi,
read the article at:
[url]http://www.alise.lv/alise/technolog.nsf/62c9b2530fea3cb8c22566ef0041c1e3/cfef6b0993adbf4a42256982004eb44f/$FILE/defrag.pdf[/url]
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Segments are the physical representation of the logical database objects. A segment is thus a subunit of a tablespace, and will be contained in a datafile. extents are subunits of a segment, and are defined as contiguous sets of Oracle blocks. Successive extents are not guaranteed to be contiguous, but within each extent the Oracle blocks are contiguous. A block is the unit of data that can be read or written to an Oracle data file, and is managed using PCT_FREE and PCT_USED, among others.
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So,
there are only one segment for an object.
That means than an segment can be spread on multiple files?
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[QUOTE][i]Originally posted by m_d_marian [/i]
[B]So,
there are only one segment for an object.
[/B][/QUOTE]
Not necessarily so. A table (object) can have partitions (subobjects), and partitions are segments. So with partitioned tables and indexes you have more than one segment for table/index.
[QUOTE]
[B]
That means than an segment can be spread on multiple files? [/B][/QUOTE]
Yes.
Jurij Modic
ASCII a stupid question, get a stupid ANSI
24 hours in a day .... 24 beer in a case .... coincidence?
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Good point J.
I went for the simple solution and ignored an important fact for larger/more complex systems.
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