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Home -> Community -> Usenet -> c.d.o.server -> Re: Rollback segments - Is it better to have 2 or 10 extents
ragu sekar wrote:
>
> Hi
>
> I read somewhere that it is better to have 10 extents for a rollback segment than just 2 extents? Pl comnfirm or contrast this/ Thanks
Not sure what your source meant by "better", but most things I have read on this topic (including most notably Cary Millsap's papers) suggest setting OPTIMAL to a size somewhere between 10 & 20 extents. The purpose of setting it this high is to reduce the chances of having the segment extend, and thus save the associated overhead. You could of course also accomplish this by simply creating rollback segs with 2 very large extents, but then such segments might be unable to extend if necesary since their NEXT extent value would be so large. So you might simply consider a value for INITIAL & NEXT of something like 256K or 512K (for garden variety segments in an OLTP database) and set OPTIMAL & MINEXTENTS to 10 extents, or so. For a Data Warehouse database i would use higher INITIAL & NEXT values, on the order of 1M.
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Vincent Ventrone | The MITRE Corp. DBA, Dept. R101 | M/S C020 vav_at_mitre.org | 202 Burlington Rd. (781) 271-7048 | Bedford, MA 01730Received on Tue Oct 19 1999 - 12:50:03 CDT