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“A university is
what a college becomes when the faculty loses interest in
students.” John Ciardi (1916 - 1986) |
Read
first then play the video:
PRF008(VIDEO)-Optimizing
Sort Operations
Optimize Sort Operations
Introduction
As a DBA, you are
responsible to optimize sort operations of your organization’s
database in case of performance problems. Your job’s
responsibilities dictate that you should be aware of the following
basic fundamental subjects:
Monitoring a sort statement
operation
Optimizing a sort statement
operation
Using the V$SYSSTAT view
SORTS (DISK)
SORTS (MEMORY)
Calculating the sort Ratio
SORT_AREA_SIZE
PGA_AGGREGATE_TARGET
Increasing the
SORT_AREA_SIZE parameter
Hands-on
In this exercise, you will
learn how to monitor and optimize sort operations.
Now, connect to SQLPlus as the SYSTEM/MANAGER user.
SQL> CONNECT system/manager AS SYSDBA
Sorting process
The Oracle Server Processes will sort as much as they can in the
memory sort area before using any disk sort space.
Sort performed destination
(Memory vs. Disk)
Now, query the V$SYSSTAT view to track the number of in-memory and
to-disk sorts, as well as the total number of rows sorted.
SQL> SELECT name, value
FROM v$sysstat
WHERE name like 'sorts%'
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Notice that the sorts (disk) number must be very low, and
the sorts (memory) number can be as high as possible.
The ‘sorts (memory)’
value is a number of times that Oracle tables were sorted in the
memory. The ‘sorts (disk)’ value is a number of times that Oracle
tables were sorted on the disk using the TEMPORARY tablespace.
Sort HIT Ratio (Memory vs.
Disk)
Now, determine the sort
ratio of the in-memory vs. to-disk sorts.
SQL> SELECT 100*(a.value-b.value)/(a.value)
AS "Sort Ratio"
FROM v$sysstat a, v$sysstat b
WHERE a.name = 'sorts (memory)'
AND b.name ='sorts (disk)'
/
Notice that the sort ratio should be greater than 95%. If
you are not using the automatic PGA memory and the number is less than
95 percent, you should greatly consider increasing the value of the
SORT_AREA_SIZE parameter. If you are using the automatic PGA memory
and the number is less than 95 percent, you should greatly consider
increasing the value of the PGA_AGGREGATE_TARGET parameter.
Increase sort area in memory
Try to increase the
SORT_AREA_SIZE parameter to 819200 bytes.
SQL> ALTER SYSTEM SET sort_area_size=819200
SCOPE=spfile
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In order for the change to take effect, the database needs
to be restarted.
Shutdown and startup the database in order to see the changes.
SQL> SHUTDOWN IMMEDIATE;
SQL> CONNECT system/manager AS SYSDBA
SQL> STARTUP
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“Success didn't
spoil me, I've always been insufferable.” Fran Lebowitz (1950
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Questions:
Q: How do you optimize a
sort operation in the Oracle SGA memory?
Q: How do you monitor a
sort operation?
Q: How do you use the
V$SYSSTAT view to check a sort usage in the SGA memory?
Q: Describe the ‘sorts
(disk)’ value in the V$SYSSTAT view.
Q: Describe the ‘sorts
(memory)’ value in the V$SYSSTAT view.
Q: How do you calculate the
sort ratio value in the SGA sort area?
Q: How do you optimize the
SORT_AREA_SIZE memory?
Q: what does the following
SQL statement?
SQL> SELECT 100*(a.value-b.value)/(a.value)
AS "Sort Ratio"
FROM v$sysstat a, v$sysstat b
WHERE a.name = 'sorts (memory)'
AND b.name ='sorts (disk)'
/
Q: What is an acceptable
range for the sort ratio in the SGA sort area?
Q: When should you consider
increasing your SORT_AREA_SIZE parameter?
Q: When should you consider
increasing your PGA_AGGREGATE_TARGET parameter?
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