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Home -> Community -> Usenet -> c.d.o.misc -> Re: Rollback Segment Trouble
A copy of this was sent to JohannesBavendiek_at_gmx.de
(if that email address didn't require changing)
On Tue, 16 Mar 1999 17:18:01 GMT, you wrote:
>That is wrong: A SELECT writes data into the rollback because in tnis way
>oracle guarantees consistent read (cursor stability).
No way. a SELECT *READS* data *FROM* a rollback segment to provide consistent reads.
Oracle does *NOT* provide cursor stability level isolation. Oracle provides
>This is the second task
>of rollback in oracle (look for detailled explanation of error ORA-1555).
>Another important information is, that the rollback segment will shrink only
>when it is used again. IMHO the resolution will be, to increase the size of
>the roolback tablespace. So there are some points to pay attation to: - the
>size of the rollback tablespace - the number of rollback segments - the
>size of the rollback segments (i.e. optimal, next, maxextents) It is
>difficult to adjust and there is no formula to calculate these parameters. I
>myselfe have still an unresolved ORA-1555-problem :-( . Here some ideas: .
>TS should be max(hwmsize) * count(rollback segments) + x (e.g. 20 percent) .
>optimal should be increased if you have lots of shrinks . the number of
>rollback segments should be big enough to avoid ORA-1555, but not so many
>that rollbacks blown up by large transactions stay long in the TS until they
>are reused. Good luck Johannes
[snip]
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Service Industries
Reston, VA USA
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