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Oracle Tips 

by Burleson Consulting

The Data Warehouse Development Life Cycle

Parallelism And Oracle Data Warehousing

The V$SYSSTAT View

Here, we see that File 16 may have a problem with excessive lock conversions. To further investigate, return to V$PING, and get the sums for File 16, as follows:

SELECT *
FROM
v$ping
SEE CODE DEPOT FOR FULL SCRIPT

Now, we can see additional detail about the contents of File 16, as shown in Table 7.2.

File #        Block #            Stat         XNC           Class #           Name          Kind
16            11                   XCUR            5           1                  ORDER         Table
16            12                   XCUR      33456          1                   ORDER         Table
16            13                   XCUR           12          1                   ORDER         Table

Table 7.2 Viewing additional file details.

From this output, we can clearly see that Block 12 is the source of our contention.

The following query against the ORDER table will reveal the contents of the rows in the data block, as shown in Table 7.3. Remember, data blocks are numbered in hex, so we convert Block 12 to a hex(c).

SELECT
rowid,
order_number,
customer_number
FROM
ORDER
SEE CODE DEPOT FOR FULL SCRIPT

ROWID                    ORDER_NUMBER               CUSTOMER_NUMBER
0000000C.0000.0008 1212                              73
0000000C.0000.0008 1213                              73
0000000C.0000.0008 1214                              73

Table 7.3 Viewing row contents.

In Table 7.3, we see that the lock conversion relates to orders placed by customer number 73. Other than a random coincidence, we can assume that there may be freelist contention in the ORDER table as new orders are added to the database. Adding new freelists will allow more concurrency during SQL INSERT operations, and the value for freelists should be reset to the maximum number of end users who are expected to be inserting an ORDER row at any given time. Unfortunately, Oracle does not allow the dynamic modification of freelists, because they are physically stored in each data block. So, the only alternative is to drop and re-create the table with more freelists in each block header. Following is the SQL used to drop and re-create the ORDER table:

CREATE TABLE ORDER_DUMMY
STORAGE (freelists 10)
AS
SELECT * FROM ORDER;

DROP TABLE ORDER;

RENAME ORDER_DUMMY TO ORDER;


This is an excerpt from "High Performance Data Warehousing".

If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.

 


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