Re: ALTER TABLE TRUNCATE PARTITION full scans partition with LOCAL indexes

From: joel garry <joel-garry_at_home.com>
Date: Tue, 8 Mar 2011 09:26:02 -0800 (PST)
Message-ID: <9e96773a-ed39-4bce-add3-977be24317ee_at_r19g2000prm.googlegroups.com>

On Mar 8, 6:20 am, Steve Howard <stevedhow..._at_gmail.com> wrote:
> On Mar 8, 9:17 am, Steve Howard <stevedhow..._at_gmail.com> wrote:
>
>
>
> > On Mar 8, 7:48 am, Randolf Geist <mah..._at_web.de> wrote:
>
> > > On Mar 7, 2:56 pm, Steve Howard <stevedhow..._at_gmail.com> wrote:
>
> > > > As you can see, the number of blocks is very close to what is
> > > > estimated it will require to truncate this partition. Also as shown,
> > > > all indexes are LOCAL, and there are no constraints either against or
> > > > on the table.
>
> > > Actually I can't see from your output that there are no global indexes
> > > since you show us only the output from a query against
> > > DBA_PART_INDEXES which by definition covers only partitioned indexes.
>
> > > So if there was a global index and your output from GV$SQL was
> > > truncated and the statement executed actually contained a "UPDATE
> > > [GLOBAL] INDEXES" then this would explain a read from the partition
> > > segment as part of the truncate to maintain the global index.
>
> > > Regards,
> > > Randolf
>
> > > Oracle related stuff blog:http://oracle-randolf.blogspot.com/
>
> > > Co-author of the "OakTable Expert Oracle Practices" book:http://www.apress.com/book/view/1430226684http://www.amazon.com/Exper......
>
> > Thanks, Randolf, sorry for the omission.  However, we definitely don't
> > have any global indexes as shown in dba_indexes...
>
> > SQL> select index_name,partitioned from dba_indexes where owner =
> > 'XWC' and table_name = 'XWCMD_XML_DATA_JOURNAL2';
>
> > INDEX_NAME                     PAR
> > ------------------------------ ---
> > SYS_IL0000268664C00008$$       YES
> > XWCMDXMLDATAJOURNAL2_IDX1      YES
> > XWCMDXMLDATAJOURNAL2_IDX2      YES
> > XWCMDXMLDATAJOURNAL2_IDX3      YES
>
> > SQL>
>
> What is interesting is that I can create an empty table and exchange
> it with the partition I am trying to truncate, and that returns almost
> instantly (less than three seconds).  Also, I tried a straight drop
> partition and that also full scans it.
>
> I also didn't have an update global indexes clause on the truncate or
> the drop.

Maybe some internal shredding winds up with some nesting, similar to the explanation in bug 5007945 but without actually hitting a bug. I have no idea why this wouldn't happen every time if that's the case, though. It would have to be something special about the data, I guess - is there something optional in your data that shreds differently? Any time there's a bug or not-a-bug, there might be related odd effects.

jg

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Received on Tue Mar 08 2011 - 11:26:02 CST