Re: Basis Question on update of Large table

Nilesh,

If you're running in log archive mode - and if you're running a production database you should be - the online logs can be reused as soon as they're archived.

If your undo tablespace has no more space your transaction will fail. If it's not full but a query started before your update was committed and the undo is no longer available your query will get ORA-1555.

Regards

John

On Sat, 20 Jan 2018, 04:04 nilesh kumar, <nileshkum_at_gmail.com> wrote:

> Forwarding it to correct group.
>
> ---------- Forwarded message ----------
> From: nilesh kumar <nileshkum_at_gmail.com>
> Date: Sat, Jan 20, 2018 at 1:13 AM
> Subject: Basis Question on update of Large table
> To: oracle-l-admins_at_freelists.org
>
>
> Hello Gurus,
>
> I have a Basic question on How an update operation work on a very large
> table in Oracle.
>
> Lets say for example, my table size is 10TB, and my database buffercache
> size is 10GB.
> I have fired an update on the 10 TB size table to update all the rows.
>
> I know that the entire 10TB table cannot be brought into the Database
> Buffer cache in one short as the Buffer is small, so does Oracle brings the
> blocks in batches ?
>
> Secondly lets say one batch of buffer blocks are updated and commit has
> not fired, to bring the next set of buffer blocks into the buffer it has to
> be pushed to the disk after the redo buffer has written the redolog files,
> but if the checkpoint is not completed then the online redologs cannot be
> reused right ?
>
> Thirdly, once the database buffer blocks are pushed to disk and commit has
> not happened and my undo tablespace size is lets say is 5GB, from where we
> would get the read consistency of the data in case a another user fires a
> select on the table ?
>
> could you please clarify my question on the update on large table.
> Sorry for asking a basic question.
>
>
>
> --
> Thanks & Regards
> Nilesh
> Oracle DBA (sqlplus "/as sysdba" is my world)
>
> "As our circle of knowledge expands, so does the circumference of darkness
> surrounding it."--Einstein
> "All men die, few men ever truly live" -- Braveheart
> "You can get help from teachers, but you are going to have to learn a lot
> by yourself, sitting alone in a room." --Dr. Seuss
> "Know me for what I do and for not what I am. Judge me for what I can do
> and not for what I have done."-Unknown
> "Don't walk in front of me, I may not follow. Don't walk behind me, I may
> not lead. Just walk beside me and be my friend."- Albert Camus
> "Never argue with an idiot. They drag you down to their level and then
> beat you with experience." - Unknown
>
>
>
> --
> Thanks & Regards
> Nilesh
> Oracle DBA (sqlplus "/as sysdba" is my world)
>
> "As our circle of knowledge expands, so does the circumference of darkness
> surrounding it."--Einstein
> "All men die, few men ever truly live" -- Braveheart
> "You can get help from teachers, but you are going to have to learn a lot
> by yourself, sitting alone in a room." --Dr. Seuss
> "Know me for what I do and for not what I am. Judge me for what I can do
> and not for what I have done."-Unknown
> "Don't walk in front of me, I may not follow. Don't walk behind me, I may
> not lead. Just walk beside me and be my friend."- Albert Camus
> "Never argue with an idiot. They drag you down to their level and then
> beat you with experience." - Unknown
>

-- 

Regards,

John

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