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Home -> Community -> Mailing Lists -> Oracle-L -> Re[2]: Re[2]: Dirty reads
Jim,
I can agree & disagree at the same time. Consider the following:
A batch job is only interested in historical data in an OLTP table. =
This
job will run for several hours due to volume of data and other considerat=
ions. =
Now the job starts at SCN 1000, but at the same time one or more
jobs/processes/forms/panels (I think you get the idea) insert data into t=
he
table. Now according to Oracle's default workings rollback is retained s=
tarting
at SCN 1000 for this job to provide a "read consistent view" of the table=
=2E =
Nice, except that this particular job will never look at those new rows o=
f data,
so why should it get a "ORA-1555 Snapshot too old" error after 2 hours of=
running?? Having the ability to "dirty read" would be a benefit in this =
case
(one of about 12 I have).
Dick Goulet
____________________Reply Separator____________________Subject: Re: Re[2]: Dirty reads
Am I the only one with no imagination? How is uncommitted data of any pr=
actical
value? Of course I can see the desire to read data as up-to-date as poss=
ible,
but if the possibility exists that the data read is 'wrong' I can't see a=
ny
advantage to this, and loads of potential harm.
Jim
>>> dgoulet_at_vicr.com 10/04/00 11:06AM >>>
The subject of "dirty reads" has been around for as long as I've worked w=
ith
Oracle, which started back in 1985. It's basically a forbidden subject. =
I know
DB2 allows this and there are others who would like it since rollback seg=
ments
would become unnecessary from their point of view (it would also make som=
e batch
processing a little more error free). But in looking at the ANSI SQL sta=
ndard
book that I've got here, dirty reads are NOT standard behavior, actually =
it's
prohibited!!
Dick Goulet.
____________________Reply Separator____________________ Author: "Ron Rogers" <RROGERS_at_galottery.org> Date: 10/3/00 1:11 PM
I don't think that Oracle would allow it because until the commit is issu=
ed the
other users see the "old" data and the user making the changes sees the n=
ew
data. If the user wants to see both copies of the data have them login tw=
ice.
One to make the changes and the other to view the original data. To circu=
mvent
Oracle's method of data integrity would destroy the foundation building b=
locks
of the database
ROR =AA=BF=AA
>>> turner_at_tellme.com 10/03/00 03:51PM >>>
Is there any way to say I want a select that won't look at the rollback
segment? The user doesn't care if it's a dirty read.
Dave Turner
Please see the official ORACLE-L FAQ: http://www.orafaq.com =
Author: David Turner
INET: turner_at_tellme.com =
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists --------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
Please see the official ORACLE-L FAQ: http://www.orafaq.com =
Author: Ron Rogers
INET: RROGERS_at_galottery.org =
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists --------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com = -- Author: INET: dgoulet_at_vicr.com = Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- = Please see the official ORACLE-L FAQ: http://www.orafaq.com -- = Author: Jim Conboy INET: Jim.Conboy_at_trw.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-LReceived on Wed Oct 04 2000 - 11:08:40 CDT
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