DBA Kevlar

I ran out of time before I was able to provide an adequate white paper this year for my EM12c presentation, but there was some valuable info in what I had started, so thought I’d turn it into a mulit-part blog post…

The Oracle Enterprise Manager, (OEM) is the standard monitoring tool for Enterprise Edition Oracle databases.  The interface allows the DBA to manage the entire Oracle stack using a single console.  The installation and interface is easy for most DBA’s to implement and utilize.  In the newest EM12c version, it encompasses integrated systems management, application management, application-to-disk and cloud management , the following documentation will include some 10g but mostly, the EM12c version of the product.

The goal for any DBA is to be notified of an issue and only notified when there is an actual issue.  One of the most common downfalls of a monitored environment is the misconception that receiving emails upon success or checks stating that a process is running, is correctly configured monitoring.  This produces an environment that leads to a “white noise” effect, where DBA’s may misinterpret a notification as one of the success notifications when a real issue has actually arisen.

The optimal design is one where redundancy checks of the monitoring system is included to ensure that if there is an issue with the monitoring environment that deters it from monitoring and sending alerts, the system has a redundant check on a secondary server that is notifying the DBA on call of the issue.   Multiple Oracle Management Server Repositories , residing on separate servers can address this, but in my opinion, would be overkill when simple additional scripts run from a cron would suffice.

OEM Basics

The Oracle Enterprise Manager, 10g and EM12c comprises of the following, basic components:

• The Oracle Management Server/Service, (OMS).
• The OMS repository database.
• The OMS Home, aka the EM state directory, which contains the bin files, log files, collection files and configuration files.
• The Agent installation, application and configuration on each monitored host server.

EM12c has the additional weblogic components included automatically, along with the Cloud support features which can be installed.

Licensing

As long as the OMS is on its own server and is only used for the OMS repository and/or an RMAN backup catalog repository, individual oracle licensing IS NOT required for the Oracle database utilized for the repositories, (Please see pg. 15 of the following PDF from Oracle.)

http://download.oracle.com/docs/cd/B19306_01/license.102/b40010.pdf

Monitoring the OEM from a secondary server:

This can be performed easily from a shell script and allows the DBA(s) to rest easy, knowing that the interface to their database environment, if impacted, will notify them from a secondary server.  This allows for redundant checks without sending an “I’m OK” notification to grant comfort:

 

       #!/usr/bin/ksh

       #----------------------------------------------------------------------------

       # Author:   Kellyn Pot’Vin

       # Redundancy Check to OEM Server to ensure EM is up and Running!

       # Verify that all parameters are set in the remote host env. vars...

       #----------------------------------------------------------------------------

       if (( $# != 2 ))

       then

           echo "usage: $0 SID hostname"

           exit 1

      fi

      #

      #----------------------------------------------------------------------------

      # Set up Oracle environment...

      #----------------------------------------------------------------------------

      export ORACLE_SID=$1

      export who_to_ping=$2

      echo "Oracle SID: "${ORACLE_SID
      export AVL_LOG=${LOG_DIR}/oem_avl.log

      export AVL_ERR=${LOG_DIR}/oem_avl.err

      export AVL_PNG_ERR=${LOG_DIR}/ping_avl.err

      #Check Repository DB for Access

      $ORACLE_HOME/bin/sqlplus oem_chk/"${pass}"@${ORACLE_SID} <<EOF

      spool ${AVL_LOG};

      select sum(1+1) from dual@grid_chk;

      spool off;

      exit;

      EOF

      cat ${AVL_LOG} | grep "ORA-" > ${AVL_ERR}

      if [ -s ${AVL_ERR} ]

      then

       echo|mail -s "No Response from Grid Control from Oracle Management Server!" "<EML_Address>"  < ${AVL_LOG}

      fi

#Check to verify that EM12C is up!  This requires SSH authentication from remote server.
ssh oracle/n0c1u3ata11@
"$OMS_HOME/bin/emctl status oms" | grep Down > ${EM_LOG}

if [ -s ${EM_LOG} ]
then
 echo|mail -s "No Response from EM12C Grid Control!" "<EML_ADDRESS>"  < ${EM_LOG}
exit
fi

      #Check Grid Server, ensure that you can ping it as well

      date

      ping -c 3 ${who_to_ping}

      if [ $? -ne 0 ]

      then

          sleep 5

          ping -c 3 ${who_to_ping}

          if [ $? -ne 0 ]

          then

              echo "`hostname` CANNOT PING ${who_to_ping} the EM Server!" > /tmp/ping.$$

       echo|mail -s "`hostname` CANNOT PING ${who_to_ping} from Oracle Managent Server!" "<EML_Address>"

       rm -f /tmp/ping.$$

           fi

      fi

      rm -f ${AVL_LOG}

      rm -f ${AVL_ERR}

exit

 

Pretty simple to schedule in cron:

0,15,30,45 * * * * /home/oracle/scripts/admin/chk_grid.ksh <dbname> <servername> > /dev/null  2>&1

I’ve chosen a 15 minute interval on the checks, but this can be done with any interval as requirements are set.

 

Escalation

Due to Sarbanes-Oxley and/or outside support contracts, an enhanced escalation process may be required.  One that can offer more choices and escalation paths then what is currently offered in the 10g and EM12c console.  A simple package/support object implementation can be created to support this type of requirement that works with OEM.  The code presented here will allow one to set the on-call DBA, scheduler and escalation outside of the OEM interface, but will all OEM alerts and escalation from the OMS will utilize the data found in the supporting tables.

I will try to upload and post the supporting schema and code soon on dbakevlar.com

 

 

Blacking out DB from Agent Side with Shell Scripts:

Blackouts can be performed via a shell script to assist in automated processes that could trigger OEM alerts, sending false notifications when a blackout script is all that is required for Unix Admin or Application support personnel.

#!/usr/local/bin/ksh

# #######################################################

# start_blackout.ksh

# Usage ./start_blackout.ksh <oracle_sid>

# Rewrite Date: 4/22/2011

# Modified by:  reckl

#########################################################

usage="$0 <db_name>"

if (($# != 1))

then

    print $usage

    exit 1

fi

ORACLE_SID=$1

sudo su - oracle -c "$AGENT_HOME/bin/emctl start blackout ${ORACLE_SID}_blackout ${ORACLE_SID}"

exit

Patching

I am a supporter of patch deployments through OEM.  If you have not configured this or are working to get this feature approved in your database environments, I highly recommend it.  In the “Deployments” tab of the EM console, first ensure that the MOS credentials is configured:

Once this has been set up for your environment, you can then designate a patching strategy to deploy to development, test and then production with a full testing cycle that will make any DBA stop quaking in their boots when they receive the notification that new patches have arrived from Oracle Support.

The Deployment Procedure Manager allows the DBA group to schedule deployments of necessary patching with the most effective schedule and little DBA involvement required.

 

The DBA can then set up patching resource allocation and requirements from the “Offline Patching” UI and choose what to install for automatically patching:

To be continued in next post….

 

 

As I continue to work on very large databases, (VLDB), I am exposed to more  opportunities to speed up IO.  This can involve Oracle’s solution of Exadata or stand alone improvements with options such as SSD, (Solid State Disk) which can offer faster IO performance at a fraction of the price.  When this option becomes a reality, there will always be non-DBA’s that advise what would best benefit from the hardware, but to take the time to research what would truly benefit is important for the DBA to perform.

The Just the Facts on Solid State Disk:

There are several types of SSD available:

• Flash memory-based
• DRAM-based
• Cache or Buffer

The SSD can have different types of host interfaces, depending on the main hardware you are interfacing with and/or vendor choices:

• PCI
• Fibre Channel
• ATA, (Serial or Parallel)
• SCSI, (Serial or Parallel)
• USB

Rarely do we get a chance to move entire Terabytes of data onto fast disk, but rather are offered limited, faster disk to utilize for crucial objects that can give us the “most bang for the buck.”   Commonly this is due to the price of these specialized and impressive IO read/write drives, but it can also be due to limitations on the hardware they are interfacing with.

As I started working on databases that utilized faster disk, with or without ASM, it became apparent that what these speedy disks were allocated to wasn’t always what SHOULD have been placed in the new location.  Where indexes, look up tables and temp tablespace experienced impressive gains vs. the standard disk drives they had formerly resided on, I have been quick to dissuade anyone from placing redo logs on SSD.

I’m going to go through what data, reports and queries that I utilize to decide what should be on fast disk, along with my benchmark findings when I did have the opportunity to create an entire database on Fusion Octal fast disk.

Getting the most out of SSD is all about getting what won’t fit in memory, (SGA and PGA) onto a faster disk.  All consistently large, [consistent] read tasks that the database must direct to disk for,  but doesn’t write as often to disk, (visualizing batch loads vs. heavy transactional) and ONCE TUNING OPPORTUNITIES HAVE BEEN EXHAUSTED, are excellent choices for research when deciding what should be placed on SSD. This information can be achieved multiple ways as a DBA.  AWR/ADDM and ASH reports can provide solid, high level data to direct you in the right direction if you are not as familiar with your data or wish to validate some of what you already know.  For those of you that do not have the tuning pack license, then Statspack can do the same.  Tracing can offer a detailed output that will tell you about objects that you are often going to slower disk for.  OEM can provide graphs that will show IO demands on a heavily “weighted” system, as can other GUI tools in the market.

 

AWR/Statspack and I/O Wait Indicators

Your group has already decided that IO is an issue and should have verified this in the top 5 wait events that can be seen through AWR or statspack.  The snapshots utilized for this examination should be times of heavy IO in the database environment as can be seen in the example Table 1.

 

Table 1

Top 5 Timed Events                                         Avg %Total
~~~~~~~~~~~~~~~~~~                                     wait   Call
Event	Waits	Time (s)	(ms)	Time	Wait Class
——————————	————	———–	——	——	———-
db file sequential read	979,382	36,066	37	45.1	User I/O
db file scattered read	5,083,058	22,401	4	28	User I/O
Direct path write temp		13,577		17	User I/O
db file parallel write	464,287	5,136	11	6.4	System I/O
direct path read temp	366,956	2,671	7	3.3	User I/O

From here, we inspect our AWR or statspack reports, there is a section that should be inspected first and foremost, referred to as Segments by Physical Reads the output from this section can be seen in Table 2.

Table 2

	Tablespace			Obj.	Physical
Owner	Name	Object Name		Type	Reads	%Total
———-	———-	——————–		—–	————	——-
SCHM_OWNR	TBLSPC1_DATA	TBL1_FILE_1		TABLE	86,788,592	47.87
SCHM_OWNR	TBLSPC2_DATA	TBL1_FILE_PK		INDEX	80,544,192	46.59
SCHM_OWNR	TBLSPC1_IDX	TBL2_MR_PK		INDEX	74,742,752	45.39
SCHM_OWNR	TBLSPC1_IDX	TBL3_M_PK		INDEX	40,924,576	28.43
SCHM_OWNR	TBLSPC2_DATA	TBL4		TABLE	26,790,464	15.52

Tuning, Always the First Step

The first step in the process is to inspect I/O issues with large objects. Is there a partitioning strategy that can take the physical reads and IO down for the objects in question? If there is not or there is still a requirement for full scans or large index or partition scans, then you need to look and see what tuning options there are for the code involved.  If there is already partitioning in place, is it the right partitioning key and/or is sub-partitioning in order.

Once this process has completed, then inspect performance for physical reads again and verify the objects in question are still a bottleneck for IO.  If so, then they may be a valid choice to relocate to a new ASM diskgroup residing on SSD.

Creating a specific ASM disk group for the SSD disk is the obvious choice, as the SSD will not be part of the standard disk groups without performance and rebalance challenges.  Once complete, you will then have the new SSD diskgroup available for use.

Inspect the sizes of the objects in left in your “top 5 physical IO objects” and decide what you move over for initial testing.  I commonly make a copy and test a copy of the objects against the code to test true performance gains, ensuring that there are no required physical storage required changes as well.  ***over what you need for capacity growth estimates.  What should you bring over next?  Now if we are still using the same reports that are showing above, I would look carefully at what I have available and would start to inspect temp usage as a possible next candidate.

It is important that if you consider temp, that it is in a “controlled” state for your environment.  It is not uncommon for many DBA’s to set TEMP to autoextend and not pay attention to temp tablespace usage.  I fully advocate the opposite and track temp usage, along with monitor alerts with scripts for anytime any user or process consumes a certain threshold per process on any of my production systems.

Considering the amount of waits on temp read and writes, tuning opportunities may be boundless on hash joins and sorting.  Low hanging fruit in these categories will involve looking for “order by’s” that have been left in for insert statements, (not sure how often I’ve seen this, but it’s a very common and an unfortunate occurrence…)  In regards to hash joins, there can be examples of wide reporting tables only one or two columns are actually required for the results and the join.  A choice of CTAS, (create table as select) of only the columns required for the process, dropping post the join to the second table, can drastically trim time and temp usage for a hash of tables that involve only a few columns on a wide table where an index is a less than efficient answer.  This choice allows the performance gain of the hash without the performance hit of swapping to temp when wide tables cause PGA to never be enough.

After tuning temp usage due to large hash joins and sorting outside of PGA, inspect the max temp tablespace required.  If this will now fit without impacting capacity planning requirements for the SSD, move the temp tablespace onto the SSD ASM disk group.

Scripts to Inspect IO Usage

There are many scripts that can be written or available on the web and in reports to inspect IO usage.  The following is a good example of one:

select

io.cnt Count,

io.event Event,

substr(io.obj,1,20) Object_Name,

io.p1 P1_Value,

f.tablespace_name Tablespace_Name

from

(

select

count(*) cnt,

round(count(*)/(60*60),2) aas,

substr(event,0,15) event,

nvl(o.object_name,decode(CURRENT_OBJ#,-1,0,CURRENT_OBJ#)) obj,

ash.p1,

o.object_type otype

from v$active_session_history ash,

all_objects o

where ( event like 'db file s%' or event like 'direct%' )

and o.object_id (+)= ash.CURRENT_OBJ#

and sample_time > sysdate - 7/(60*24)

group by

substr(event,0,15) ,

CURRENT_OBJ#, o.object_name ,

o.object_type ,

ash.p1

) io,

dba_data_files f

where

f.file_id = io.p1

and f.tablespace_name not like '%RAM%' –-exclude SSD objects

Order by io.cnt desc

/

 

COUNT	EVENT	OBJECT_NAME	P1_Value	TABLESPACE_NAME
122	db file sequent	TBL1_CHAIN	102	N_DATA
33	db file sequent	HH_TBL1_FDX01	161	H_INDX1
28	db file sequent	CA_TBL2_PK	270	C_INDX
25	db file sequent	I_TBL3_IDX02	225	I_INDX2
21	db file sequent	E_TBL4	43	E_DATA
20	direct path rea	I_MRG_TBL	75	M_DATA
23	db file scatter	C_TBL3	50	C_DATA

 

The above script gives you clear examples of what objects you should point your research to, first indexes, (sequential) and in this case, a look up table, (direct path read).

Building a Database Entirely on SSD

We were given this opportunity recently to test performance gains and decide if budget should be set aside for investing in the hardware to build entire databases on SSD vs. strategic objects within a database.  We have a process that takes approximately five days to aggregate a snapshot in time, up to 12TB of data.  The goal was to see, could we accomplish this in two days if given all SSD for the database vs. a combination of standard disks on a disk array and SSD for high read/write data.

This sounds like a slam dunk, but it is more challenging than one might think.  There are small things to that have to be updated in the database, such as system statistics in 10g to ensure the database knows fully the gift you have granted it, but then you may also need to make significant logical changes to take advantage of the hardware due to limitations in CPU and memory per process.  The build was on a server that utilized hyper-threading and some of the “performance settings” actually appeared to work against the database vs. the lesser setting that might stripe the CPU usage more efficiently.  The graph below show the hits against the first 32 of “hyper-threaded” 64 CPU’s:

Figure 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This graph in Figure 1 only shows CPU usage over a small snapshot of time, but over long intervals, it showed the same differing data vs. SAR or other reports from the Admin side-  the database continued to hit the same CPU’s over and over, leaving other CPU’s untouched for extended periods of time.  This did not bode well for the database performance, high read/write capability or not.

 

The build time improvements were impressive, but the one thing that must be included is that the improvement in performance was not just a hardware improvement step.  There was first the additional hardware and then a tuning process at the database level to ensure the processes were able to achieve the best performance the solid state disk offered it, (comparison of columns New Run Time against the Final Run Time in Figure 2.)

Process Step	Standard Disk/SSD	Total Min.	SSD Without Tuning	New Run Time	Initial Perf. Gain	SSD With Tuning	Final Run Time	Total Perf. Gain
DIM Table 1 CTAS	4 HOURS 20 MINUTES 27 SECS	260 min	3 HOURS 38 MINUTES 24 SECS	218 min	19%	2 HOURS 43 MINUTES 45 SECS	164 min	58%
CTAS Table 2	4 HOURS 23 MINUTES 11 SECS	263 min	0 HOURS 16 MINUTES 2 SECS	16 min	16 Times Perf	0 HOURS 19 MINUTES 8 SECS	No Tuning	N/A
CTAS Table 3	1 HOURS 29 MINUTES 21 SECS	89 min	0 HOURS 44 MINUTES 27 SECS	44 min	2 Times Perf.	0 HOURS 57 MINUTES 19 SECS	No Tuning	N/A
CTAS Table 4	2 HOURS 55 MINUTES 58 SECS	175 min	0 HOURS 42 MINUTES 16 SECS	42 min	4 Times Perf.	0 HOURS 47 MINUTES 55 SECS	No Tuning	N/A
CTAS Table 5	10 HOURS 7 MINUTES 41 SECS	607 min	1 HOURS 50 MINUTES 7 SECS	110 min	6 Times Perf.	1 HOURS 42 MINUTES 6 SECS	No Tuning	N/A
CTAS Table 6	11 HOURS 32 MINUTES 40 SECS	692 min	4 HOURS 51 MINUTES 17 SECS	291 min	2 Times Perf.	5 HOURS 9 MINUTES 26 SECS	No Tuning	N/A
Multiple Table Aggregation	25 HOURS 15 MINUTES 3 SECS	1515 min	9 HOURS 58 MINUTES 1 SECS	598 min	3 Times Perf.	5 HOURS 16 MINUTES 31 SECS	316 min	5 Times Perf.
Summary Table 1 Agg.	25 HOURS 24 MINUTES 35 SECS	1524 min	10 HOURS 0 MINUTES 20 SECS	600 min	3 Times Perf.	5 HOURS 18 MINUTES 14 SECS	318 min	5 Times Perf.
Summary Table 2 Agg.	25 HOURS 23 MINUTES 56 SECS	1523 min	10 HOURS 7 MINUTES 22 SECS	607 min	3 Times Perf.	5 HOURS 25 MINUTES 54 SECS	325 min	5 Times Perf.
Index Creation Table 1	1 HOURS 16 MINUTES 33 SECS	76 min	0 HOURS 53 MINUTES 42 SECS	54 min	39%	0 HOURS 53 MINUTES 14 SECS	No Tuning	N/A
Index Creation Table 2	1 HOURS 22 MINUTES 55 SECS	82 min	0 HOURS 59 MINUTES 55 SECS	60 min	28%	0 HOURS 59 MINUTES 6 SECS	No Tuning	N/A
CTAS Aggr Table 3	6 HOURS 36 MINUTES 20 SECS	396 min	3 HOURS 21 MINUTES 18 SECS	201 min	50%	3 HOURS 13 MINUTES 38 SECS	No Tuning	N/A
Index Creation Table 3	0 HOURS 52 MINUTES 2 SECS	52 min	0 HOURS 40 MINUTES 3 SECS	40 min	24%	0 HOURS 48 MINUTES 15 SECS	No Tuning	N/A
CTAS Aggr. Table 4	2 HOURS 41 MINUTES 13 SECS	161 min	1 HOURS 32 MINUTES 8 SECS	92 min	43%	1 HOURS 28 MINUTES 25 SECS	No Tuning	N/A
CTAS Aggr Table 5	3 HOURS 46 MINUTES 59 SECS	226 min	2 HOURS 58 MINUTES 29 SECS	179 min	21%	2 HOURS 55 MINUTES 20 SECS	No Tuning	N/A
CTAS Aggr. Table 6	0 HOURS 51 MINUTES 27 SECS	51 min	0 HOURS 36 MINUTES 46 SECS	37 min	28%	0 HOURS 34 MINUTES 33 SECS	No Tuning	N/A
Insert to Table 6	0 HOURS 5 MINUTES 24 SECS	5 min	0 HOURS 5 MINUTES 6 SECS	5 min	NONE	0 HOURS 4 MINUTES 52 SECS	5 min	NONE
Update to Table 6	26 HOURS 40 MINUTES 41 SECS	1640 min	25 HOURS 9 MINUTES 52 SECS	1510 min	8%	17 HOURS 44 MINUTES 2 SECS	1084 min	44%
CTAS Table 7	1 HOURS 1 MINUTES 48 SECS	61 min	0 HOURS 7 MINUTES 43 SECS	8 min	13 Times Perf.	0 HOURS 6 MINUTES 37 SECS	No Tuning	N/A
CTAS Aggr Table 8	0 HOURS 28 MINUTES 31 SECS	28 min	0 HOURS 22 MINUTES 12 SECS	22 min	22%	0 HOURS 19 MINUTES 25 SECS	No Tuning	N/A
CTAS Mod TBLS 9/10	1 HOURS 42 MINUTES 36 SECS	102 min	1 HOURS 42 MINUTES 22 SECS	102 min	NONE	1 HOURS 39 MINUTES 25 SECS	No Tuning	N/A
CTAS Table Aggr. 11	2 HOURS 26 MINUTES 58 SECS	147 min	1 HOURS 29 MINUTES 53 SECS	90 min	49%	1 HOURS 24 MINUTES 42 SECS	No Tuning	N/A
CTAS Aggr. Table 12	7 HOURS 24 MINUTES 44 SECS	445 min	6 HOURS 7 MINUTES 48 SECS	368 min	18%	6 HOURS 6 MINUTES 40 SECS	No Tuning	N/A
CTAS Aggr. Table 13	6 HOURS 47 MINUTES 31 SECS	408 min	4 HOURS 38 MINUTES 1 SECS	278 min	32%	5 HOURS 5 MINUTES 32 SECS	No Tuning	N/A
CTAS Aggr. Table 14	25 HOURS 23 MINUTES 32 SECS	1524 min	10 HOURS 9 MINUTES 51 SECS	610 min	3 Times Perf.	5 HOURS 27 MINUTES 17 SECS	327 min	5 Times Perf.
CTAS Aggr. Table 15	1 HOURS 21 MINUTES 59 SECS	82 min	0 HOURS 22 MINUTES 49 SECS	23 min	65%	0 HOURS 4 MINUTES 33 SECS	4 min	20 Times Perf.
Update to Table 13	0 HOURS 12 MINUTES 45 SECS	13 min	0 HOURS 49 MINUTES 58 SECS	50 min	3 Times LOSS!!	0 HOURS 1 MINUTES 22 SECS	1 min	9 Times Perf.

Figure 2

I must note that what challenged us in unresolved issues were waits on CPU due to hyper-threaded CPU issues. 

Tuning involved for the third columns time elapsed involved the following:

• Bind variable additions
• Literal additions where bind peeking was an issue.
• A change from ASSM, (Automatic Segment Space Management) to manual segment space management where freelists could be set at the object level, (dynamically allocated freelists were not able to adjust quickly enough for some of the load processes…)
• Changes to initial transactions, percent free and parallel that made sense, (upping it for some, downgrading it for others that did not work with the partitioning or a need for partitioning…)

Inspecting I/O by SQL_ID

This script, (adopted from Tim Gorman’s sqlhistory.sql from, www.evdbt.com)  does a wonderful job of pulling a clean, clear picture of what physical and logical I/O is occurring in a single SQL_ID, seen here in Table 3 :

Table 3

+————————————————————————————————–+
	Plan HV     Min Snap  Max Snap  Execs       LIO            PIO            CPU         Elapsed
+————————————————————————————————–+
	1766271350  659       659       1           593,134,283    12,961,814     14,657.45   15,067.05
+————————————————————————————————–+
========== PHV = 1766271350==========
First seen from “07/15/11 13:00:31″ (snap #659)
Last seen from  “07/15/11 13:00:31″ (snap #659)
Execs          LIO            PIO            CPU            Elapsed
=====          ===            ===            ===            =======
1              593,134,283    12,961,814     14,657.45      15,067.05
Plan hash value: 1766271350

 

TQ	IN-OUT	PQ Distrib
0	CREATE TABLE STATEMENT					1543M(100)
1	PX COORDINATOR
2	PX SEND QC (RANDOM)	:TQ10001	464M	397G		4128K  (7)
Q1,01	P->S	QC (RAND)
3	LOAD AS SELECT
Q1,01	PCWP
4	PX RECEIVE		464M	397G		4128K  (7)
Q1,01	PCWP
5	PX SEND RANDOM LOCAL	:TQ10000	464M	397G		4128K  (7)
Q1,00	P->P	RANDOM LOCA
6	PX PARTITION LIST ALL		464M	397G		4128K  (7)	1	1000
Q1,00	PCWC
7	HASH JOIN RIGHT OUTER		464M	397G	14G	4128K  (7)
Q1,00	PCWP
8	TABLE ACCESS FULL	HDN_TBL	231M	112G		576K (22)	1	1000
Q1,00	PCWP
9	HASH JOIN RIGHT OUTER		464M	171G	6967M	1551K  (7)
Q1,00	PCWP
10	TABLE ACCESS FULL	HD_TBL	310M	50G		144K (34)	1	1000
Q1,00	PCWP
11	TABLE ACCESS FULL	H_TBL	464M	95G		339K (13)	1	1000
Q1,00	PCWP

 

 

Summary Execution Statistics Over Time
Avg                 Avg
Snapshot                          Avg LIO             Avg PIO          CPU (secs)      Elapsed (secs)
Time                 Execs            Per Exec            Per Exec            Per Exec            Per Exec
———— ——– ——————- ——————- ——————- ——————-
15-JUL 13:00        1      593,134,283.00       12,961,814.00           14,657.45           15,067.05
——– ——————- ——————- ——————- ——————-
avg                                 593,134,283.00       12,961,814.00           14,657.45           15,067.05
sum                        1
Per-Plan Execution Statistics Over Time
Avg                 Avg
Plan Snapshot                          Avg LIO             Avg PIO          CPU (secs)      Elapsed (secs)
Hash Value Time            Execs            Per Exec            Per Exec            Per Exec            Per Exec
———- ———— ——– ——————- ——————- ——————- ——————-
1766271350 15-JUL 13:00        1      593,134,283.00       12,961,814.00           14,657.45           15,067.05
**********              ——– ——————- ——————- ——————- ——————-
avg                                                        593,134,283.00       12,961,814.00           14,657.45           15,067.05
sum                                               1

+—————————————————————————————————————————

This report clearly shows the amount of logical vs. physical I/O coming from the statement in question.  This gives the DBA a clear indicator if any object in the poor performing process would benefit a move to SSD or if tuning is in order to eliminate the I/O performance challenge.  A combination of both may be chosen, as there are multiple right outer hash-joins which clearly show as the performance hit in the time elapsed and in the temp tablespace usage/significant I/O categories, (note that the process needs to scan ALL the partitions for the objects in question…)

SSD and Forced Hash Joins on Indexes

When a database design is impacted by the front-end tool required to present data in a proper format, such as Business Analytics Software, the price can be high to the DBA who has to manage resource usage.  Many times the data must be presented in a very flat, wide format and requires a large amount of data pulled across a network interface.  This can be in anywhere from a couple 100GB’s to multiple Terabytes.  When you are the DBA looking at ways to increase performance when logical performance tuning is limited, solid state disk can offer you gains not offered anywhere else.

Business Analytics Software often will query a few 100GB to 1TB objects, hash join and then perform an order by.  For the DBA, to create an index, then using a hint to force a hash join between an index and the large table can improve performance greatly, but to move the index onto SSD can increase the hash and limit the requirements for SSD at the same time.

create table    new_ordertmp_tbl  compress pctfree 0 tablespace data_1 as

SELECT /*+ USE_HASH(t,i) INDEX_FFS(i,I_TBL2_IDX) INDEX(t,CT1) */

cast(MOD(t.i_id, 1000) as number(3)) im_key

, LEAST(ROUND(MONTHS_BETWEEN(:b1,  t.t_dt) + .4999 ), 48) AS r_key , t.i_id AS ib_id

, t.m_id, t.t_dt, cast(:b5 as varchar2(5)) m_cd, FIRST_VALUE(i.ib_id) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

) AS ibcid, t.t_nbr, cast(TO_NUMBER(TO_CHAR(FIRST_VALUE(t.t_dt) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

), ''YYYYMMDD'')) as number(8)) AS d_id,

FIRST_VALUE(DECODE(t.oct_cd, NULL, 'O','W', 'O', 'E', 'O', 'R', 'R', 'F')

) OVER(PARTITION BY t.d_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

) AS tct_cd, SUM(t.ot_amt) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt) AS ot_amt

, FIRST_VALUE(NVL(t.pmt_cd, ''U'')) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

) AS pmt_cd, SUM(t.i_cnt) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt) AS i_cnt

, FIRST_VALUE(t.cs_cd IGNORE NULLS) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

) AS cs_cd, FIRST_VALUE(t.cc_cd IGNORE NULLS) OVER(

PARTITION BY t.i_id, t.m_id, t.t_nbr,t.t_dt ORDER BY t.t_dt ASC

) AS cc_cd, t.oct_cd

FROM CT_TBL1 t, I_TBL2 i

WHERE t.m_id = :b5

AND t.t_dt BETWEEN  :b1  AND  :b2 AND i.ibid = t.i_id

order by i.i_id; 

Object Sizes:

CT_TBL1, partition 7= 800GB

I_TBL2=1.2TB

While the I_TBL2_IDX, the index created on the I_TBL2 and possessing only the columns required for this routinely run query and leading with the I_ID column, is only 200GB.

Execution Plan for Query:

Table 4

Description	Object	Cost	Cardinality	Bytes	PartitionID
SELECT STATEMENT, GOAL = ALL_ROWS		107587	16356015	10079496
WINDOW SORT		107587	16356015	10079496
WINDOW BUFFER		107587	16356015	10079496
WINDOW SORT		107587	16356015	10079496
WINDOW SORT		107587	16356015	10079496
FILTER
HASH JOIN		107371	16356015	10079496
PARTITION LIST SINGLE		330	16356015	8166868	7
TABLE ACCESS FULL	CT_TBL1	330	16356015	8166868	7
INDEX FAST FULL SCAN	I_TBL2_IDX	23597	6399400008	2120000

The hash join is thus, decreased to a total size of 1TB, vs. the much larger size it would have been if the hash join would have been run against the table.  By running it with the index residing on solid state disks, the actual performance to create the table from the CTAS in question was increased by 12 fold.

What does the IO look like on the solid state disk vs. the old standard disk?  The differences are startling when viewed through iostat, (table 5).

Table 5

Device:	rsec/s	wsec/s	avgqu-sz	%util
Raid 5 Disk	55200	30224	215.72	84.03
SSD	52394.67	41306	223.74	7.49

As you can see, the IO is much less impacting on the SSD than the standard disk.

Via graphs, such as from Cacti, the differences in IO throughput can be seen for standard disk, (figure 3) and solid state disk, (figure 4.)

Figure 3

 

 

 

 

 

Figure 4

 

 

 

 

 

 

 

Summary

Solid state disk is here to stay and often will be seen as a “silver bullet” for production I/O issues.  The goal of the DBA is to utilize this technology in a way that does not replace logical tuning and focus instead, in ways that may actually support positive changes enforcing both physical and logical tuning to get the most out of the new hardware available on the market today.