Re: newbee ROLLBACK/ COMMIT

A copy of this was sent to spectre_at_hkstar.com (Steve A) (if that email address didn't require changing) On Thu, 12 Aug 1999 07:49:32 +0800, you wrote:

>AHH!
>this explains a lot,
>
>esp. why I keep getting record in use messages from the remote view in
>foxpro.
>
>yes I'm client server
>I have the procedures on the oracle server then pass parameters from
>foxpro, to update the tables.
>
>so how do I enable dead client detection.
>

you do this with sqlnet configuration. its done in the sqlnet.ora file. please see the related SQL*net documentation for instructions.

>also you explain that I can see the row if I select it back, then
>further down you say it will not appear in a select.
>do you mean I have to use a unique key field to get it.
>

What i was trying to say was:

• If your transaction creates/modifies/deletes data -- SUBSEQUENT statements in your transaction can see that change but no one else can.
• the statement that makes the change *cannot* see that change, so for example: "insert into T select * from T" is deterministic, the select * from T part of the INSERT INTO T will never see any of the 'new rows' being added. The select component of that statement is consistent with repect to the point in time that the query (the insert) began.

So, I guess the first point is the short, easy way to say it. subsequent statements in your transaction can see your changes but no one else can.

>steve
>
>
>Thomas Kyte <tkyte_at_us.oracle.com> wrote:
>
>> A copy of this was sent to spectre_at_hkstar.com (Steve A)
>> (if that email address didn't require changing)
>> On Wed, 11 Aug 1999 18:25:31 +0800, you wrote:
>>
>> >Hi,
>> >I'm a bit confused by the rollback command, I understand the function of
>> >commit ,rollback & savepoint
>> >
>> >But have the following questions.
>> >1. do I have to use the savepoint command?
>>
>> no
>>
>> >2. if my client crashes during the transaction , how long does the "temp
>> >changes" sit around or is it dropped when I crash
>> >
>>
>> depends on the circumstances. if you are client server, and you do not have
>> dead client detection enabled, it may sit around until you manually kill the
>> session or restart the database.
>>
>> >3. if my client crashes, then re-logs in & then re-does the work and
>> >commits , will the server throw away the old crashed session or try to
>> >commit it when I issue a commit in a new session.
>> >
>>
>> the 2 sessions are mutually exclusive of each other - they have nothing
>> whatsoever to do with each other. if you client crashes and the server can
>> detect it -- it'll be rolled back and cleaned up (dead client detection).
> OTOH
>> -- if the server cannot detect it, any outstanding locks gathered by that
>> session (the crashed one) will stay in place.
>>
>> when your client logs back in -- they may not be able to redo the work YET
> since
>> the crashed session may still be there.
>>
>>
>> >4. can anybody see any "temp" changes made to the database (including
>> >my client) before the commit has been issued.
>> >
>>
>> you can see your changes -- if you insert a row and select it back it, you'll
>> see it. No one else will until you commit.
>>
>> You can see your changes.
>> No one else can.
>>
>> The statement that makes a change cannot 'see' its own changes. For example:
>>
>> insert into T select * from T;
>>
>> The select * from T will not (fortunately) "see" any of the new rows being
>> inserted into T. The select will see T as it was BEFORE the insert started
>> (otherwise that would be an easy way to write an infinite loop)...
>>
>>
>> >5. how long between the commit & the changes becomming visible in the
>> >database
>> >
>>
>> immediate -- you commit, they are there.
>>
>> >steve
>> >

--
See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'... Current article is "Part I of V, Autonomous Transactions" updated June 21'st  

Thomas Kyte                   tkyte_at_us.oracle.com
Oracle Service Industries     Reston, VA   USA

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Thu Aug 12 1999 - 06:06:42 CDT