Example 2: Unable to Get Desired Throughput

Problem Description

CustomerB was in the midst of implementing a new application, performing stress tests before going into production. While performing the stress test, the database server could not ramp up to the desired number of client applications while achieving the required response times.

Problem Analysis and Resolution

Step 1: Examine the Database and Database Manager Configuration Parameters
Database manager configuration

The three parameters in the database manager configuration that stand out are highlighted in bold below. In this case, the application is mainly an online application; therefore, intra-partition parallelism should be disabled. Because there will be a large number of concurrent applications, the sort heap threshold (SHEAPTHRES) will need to be high; however, the existing value is sufficient.

Node type = Database Server with local and remote clients

Database manager configuration release level            = 0x0900

CPU speed (millisec/instruction)             (CPUSPEED) = 8.580921e-07

Max number of concurrently active databases     (NUMDB) = 8
Data Links support                          (DATALINKS) = NO
Federated Database System Support           (FEDERATED) = YES
Transaction processor monitor name        (TP_MON_NAME) =

Default charge-back account           (DFT_ACCOUNT_STR) =

Java Development Kit 1.1 installation path   (JDK_PATH) =

Diagnostic error capture level              (DIAGLEVEL) = 3
Notify Level                              (NOTIFYLEVEL) = 3
Diagnostic data directory path               (DIAGPATH) = /products/db2/fsprdi/sqllib/db2dump

Default database monitor switches
  Buffer pool                         (DFT_MON_BUFPOOL) = OFF
  Lock                                   (DFT_MON_LOCK) = OFF
  Sort                                   (DFT_MON_SORT) = OFF
  Statement                              (DFT_MON_STMT) = OFF
  Table                                 (DFT_MON_TABLE) = OFF
  Unit of work                            (DFT_MON_UOW) = OFF
Monitor health of instance and databases   (HEALTH_MON) = OFF

SYSADM group name                        (SYSADM_GROUP) = DBA
SYSCTRL group name                      (SYSCTRL_GROUP) = DBASCTL
SYSMAINT group name                    (SYSMAINT_GROUP) = DBAMNT

Database manager authentication        (AUTHENTICATION) = SERVER
Cataloging allowed without authority   (CATALOG_NOAUTH) = NO
Trust all clients                      (TRUST_ALLCLNTS) = YES
Trusted client authentication          (TRUST_CLNTAUTH) = CLIENT
Use SNA authentication                   (USE_SNA_AUTH) = NO
Bypass federated authentication            (FED_NOAUTH) = NO

Default database path                       (DFTDBPATH) = /products/db2/fsprdi

Database monitor heap size (4KB)          (MON_HEAP_SZ) = 56
UDF shared memory set size (4KB)           (UDF_MEM_SZ) = 256
Java Virtual Machine heap size (4KB)     (JAVA_HEAP_SZ) = 2048
Audit buffer size (4KB)                  (AUDIT_BUF_SZ) = 0
Backup buffer default size (4KB)            (BACKBUFSZ) = 1024
Restore buffer default size (4KB)           (RESTBUFSZ) = 1024

Sort heap threshold (4KB)                  (SHEAPTHRES) = 100000

Directory cache support                     (DIR_CACHE) = YES

Application support layer heap size (4KB)   (ASLHEAPSZ) = 15
Max requester I/O block size (bytes)         (RQRIOBLK) = 32767
Query heap size (4KB)                   (QUERY_HEAP_SZ) = 16000
DRDA services heap size (4KB)            (DRDA_HEAP_SZ) = 128

Priority of agents                           (AGENTPRI) = SYSTEM
Max number of existing agents               (MAXAGENTS) = 200
Agent pool size                        (NUM_POOLAGENTS) = 4 (calculated)
Initial number of agents in pool       (NUM_INITAGENTS) = 0
Max number of coordinating agents     (MAX_COORDAGENTS) = MAXAGENTS
Max no. of concurrent coordinating agents  (MAXCAGENTS) = MAX_COORDAGENTS
Max number of logical agents          (MAX_LOGICAGENTS) = MAX_COORDAGENTS

Keep fenced process                        (KEEPFENCED) = YES
Number of pooled fenced processes         (FENCED_POOL) = MAX_COORDAGENTS
Initialize DARI process with JVM       (INITFENCED_JVM) = NO
Initial number of fenced DARI process  (NUM_INITFENCED) = 0
Index re-creation time                       (INDEXREC) = RESTART

Transaction manager database name         (TM_DATABASE) = 1ST_CONN
Transaction resync interval (sec)     (RESYNC_INTERVAL) = 180

SPM name                                     (SPM_NAME) = it_ibm60
SPM log size                          (SPM_LOG_FILE_SZ) = 256
SPM resync agent limit                 (SPM_MAX_RESYNC) = 20
SPM log path                             (SPM_LOG_PATH) =

TCP/IP Service name                          (SVCENAME) = 50000
Discovery mode                               (DISCOVER) = SEARCH
Discovery communication protocols       (DISCOVER_COMM) = TCPIP
Discover server instance                (DISCOVER_INST) = ENABLE

Maximum query degree of parallelism   (MAX_QUERYDEGREE) = ANY
Enable intra-partition parallelism     (INTRA_PARALLEL) = NO

No. of int. communication buffers(4KB)(FCM_NUM_BUFFERS) = 1024
Node connection elapse time (sec)         (CONN_ELAPSE) = 10
Max number of node connection retries (MAX_CONNRETRIES) = 5
Max time difference between nodes (min) (MAX_TIME_DIFF) = 60

db2start/db2stop timeout (min)        (START_STOP_TIME) = 10
Database configuration for database sample

The three parameters in the database manager configuration that stand out are highlighted in bold below.

  • Because the applications will be performing a lot of inserts/updates/deletes, the log buffer size (LOGBUFSZ) will be important. However, the log buffer is sized adequately for this workload.

  • Because this is an online application, the sort list heap (SORTHEAP) should not be too large. When it is too large, the DB2 optimizer will tend to favor sorts over index scans, and with a large number of concurrent applications, sorting will be detrimental to performance.

  • In this case, the default buffer pool size (BUFFPAGE) is 1,000 4-KB pages. To determine the real size of the buffer pool, use the following statement:

    select * from syscat.bufferpools
    
    • In this case, there is only one buffer pool (IBMDEFAULTBP), and it has a size of 5,000 4-KB pages.

    • This is a rather small buffer pool; therefore, increasing the size of the buffer pool likely will help performance.

Database configuration release level                    = 0x0a00
Database release level                                  = 0x0a00

Database territory                                      = US
Database code page                                      = 819
Database code set                                       = ISO8859-1
Database country/region code                            = 1

Dynamic SQL Query management           (DYN_QUERY_MGMT) = DISABLE

Discovery support for this database       (DISCOVER_DB) = ENABLE

Default query optimization class         (DFT_QUERYOPT) = 5
Degree of parallelism                      (DFT_DEGREE) = 1
Continue upon arithmetic exceptions   (DFT_SQLMATHWARN) = NO
Default refresh age                   (DFT_REFRESH_AGE) = 0
Number of frequent values retained     (NUM_FREQVALUES) = 10
Number of quantiles retained            (NUM_QUANTILES) = 20

Backup pending                                          = NO

Database is consistent                                  = NO
Rollforward pending                                     = NO
Restore pending                                         = NO

Multi-page file allocation enabled                      = NO

Log retain for recovery status                          = NO
User exit for logging status                            = NO

Data Links Token Expiry Interval (sec)      (DL_EXPINT) = 60
Data Links Write Token Init Expiry Intvl(DL_WT_IEXPINT) = 60
Data Links Number of Copies             (DL_NUM_COPIES) = 1
Data Links Time after Drop (days)        (DL_TIME_DROP) = 1
Data Links Token in Uppercase                (DL_UPPER) = NO
Data Links Token Algorithm                   (DL_TOKEN) = MAC0

Database heap (4KB)                            (DBHEAP) = 1200
Size of database shared memory (4KB)  (DATABASE_MEMORY) = AUTOMATIC
Catalog cache size (4KB)              (CATALOGCACHE_SZ) = (MAXAPPLS*4)
Log buffer size (4KB)                        (LOGBUFSZ) = 256
Utilities heap size (4KB)                (UTIL_HEAP_SZ) = 5000
Buffer pool size (pages)                     (BUFFPAGE) = 1000
Extended storage segments size (4KB)    (ESTORE_SEG_SZ) = 16000
Number of extended storage segments   (NUM_ESTORE_SEGS) = 0
Max storage for lock list (4KB)              (LOCKLIST) = 100

Max size of appl. group mem set (4KB) (APPGROUP_MEM_SZ) = 20000
Percent of mem for appl. group heap   (GROUPHEAP_RATIO) = 70
Max appl. control heap size (4KB)     (APP_CTL_HEAP_SZ) = 128

Sort heap thres for shared sorts (4KB) (SHEAPTHRES_SHR) = (SHEAPTHRES)
Sort list heap (4KB)                         (SORTHEAP) = 1024
SQL statement heap (4KB)                     (STMTHEAP) = 4096
Default application heap (4KB)             (APPLHEAPSZ) = 256
Package cache size (4KB)                   (PCKCACHESZ) = (MAXAPPLS*8)
Statistics heap size (4KB)               (STAT_HEAP_SZ) = 4384

Interval for checking deadlock (ms)         (DLCHKTIME) = 10000
Percent. of lock lists per application       (MAXLOCKS) = 10
Lock timeout (sec)                        (LOCKTIMEOUT) = -1

Changed pages threshold                (CHNGPGS_THRESH) = 60
Number of asynchronous page cleaners   (NUM_IOCLEANERS) = 10
Number of I/O servers                   (NUM_IOSERVERS) = 10
Index sort flag                             (INDEXSORT) = YES
Sequential detect flag                      (SEQDETECT) = YES
Default prefetch size (pages)         (DFT_PREFETCH_SZ) = 32

Track modified pages                         (TRACKMOD) = OFF

Default number of containers                            = 1
Default tablespace extentsize (pages)   (DFT_EXTENT_SZ) = 32

Max number of active applications            (MAXAPPLS) = AUTOMATIC
Average number of active applications       (AVG_APPLS) = 1
Max DB files open per application            (MAXFILOP) = 64

Log file size (4KB)                         (LOGFILSIZ) = 1000
Number of primary log files                (LOGPRIMARY) = 3
Number of secondary log files               (LOGSECOND) = 2
Changed path to log files                  (NEWLOGPATH) =
Path to log files                                       = /databases/sample/logs
Overflow log path                     (OVERFLOWLOGPATH) =
Mirror log path                         (MIRRORLOGPATH) =
First active log file                                   =
Block log on disk full                (BLK_LOG_DSK_FUL) = NO
Percent of max active log space by transaction(MAX_LOG) = 0
Num. of active log files for 1 active UOW(NUM_LOG_SPAN) = 0

Group commit count                          (MINCOMMIT) = 1
Percent log file reclaimed before soft chckpt (SOFTMAX) = 100
Log retain for recovery enabled             (LOGRETAIN) = OFF
User exit for logging enabled                (USEREXIT) = OFF

Auto restart enabled                      (AUTORESTART) = ON
Index re-creation time                       (INDEXREC) = SYSTEM (RESTART)
Default number of loadrec sessions    (DFT_LOADREC_SES) = 1
Number of database backups to retain   (NUM_DB_BACKUPS) = 12
Recovery history retention (days)     (REC_HIS_RETENTN) = 366

TSM management class                    (TSM_MGMTCLASS) =
TSM node name                            (TSM_NODENAME) =
TSM owner                                   (TSM_OWNER) =
TSM password                             (TSM_PASSWORD) =
Step 2: Make Changes Based on the Examination of Configuration Information

The size of the buffer pool was increased as follows:

alter bufferpool IBMDEFAULTBP immediate size 500000
Step 3: Retest

After increasing the size of the buffer pool, the response time improved, and more concurrent users were able to connect to the database and run the applications; however, the system was still unable to attain the required number of applications.

Step 4: Check System for I/O Bottlenecks, Excess Paging, or Other Processes/Applications Using Excess System Resources

This requires operating system tools such as vmstat, iostat, and/or top to capture the memory, I/O, and process level information. It is important to capture the snapshots from these tools over a period of time, not taking just one snapshot, especially because the first line of the output of the vmstat and iostat tools contains average information since the server was started and is not really useful in analyzing a problem.

While the applications are running, and particularly when the system begins to stop responding, capture iostat output, as follows:

iostat 5 > iostat.out

Next, examine the iostat.out file, below:

Disks:        % tm_act     Kbps      tps    Kb_read   Kb_wrtn
Hdisk0           2.6      13.2       7.3         19         0
Hdisk1           1.8       9.2       7.3         19         0
Hdisk2           1.8       9.2       7.3         19         0
Hdisk3           1.8       9.2       7.3         19         0
Hdisk4           1.8       9.2       7.3         19         0
Hdisk5          42.8     213.2      107.3       237       286
Hdisk6           1.8       9.2       7.3         19         0
Hdisk7           1.8       9.2       7.3         19         0
Hdisk8           1.8       9.2       7.3         19         0
Hdisk9           1.8       9.2       7.3         19         0
cd0              0.0       0.0       0.0          0         0

Disks:        % tm_act     Kbps      tps    Kb_read   Kb_wrtn
Hdisk0           2.6      13.2       7.3         19         0
Hdisk1           1.8       9.2       7.3         19         0
Hdisk2           1.8       9.2       7.3         19         0
Hdisk3           1.8       9.2       7.3         19         0
Hdisk4           1.8       9.2       7.3         19         0
Hdisk5          47.1     234.7      111.3       261       292
Hdisk6           1.8       9.2       7.3         19         0
Hdisk7           1.8       9.2       7.3         19         0
Hdisk8           1.8       9.2       7.3         19         0
Hdisk9           1.8       9.2       7.3         19         0
cd0              0.0       0.0       0.0          0         0

Disks:        % tm_act     Kbps      tps    Kb_read   Kb_wrtn
Hdisk0           2.6      13.2       7.3         19         0
Hdisk1           1.8       9.2       7.3         19         0
Hdisk2           1.8       9.2       7.3         19         0
Hdisk3           1.8       9.2       7.3         19         0
Hdisk4           1.8       9.2       7.3         19         0
Hdisk5          43.3     214.6      109.8       283       239
Hdisk6           1.8       9.2       7.3         19         0
Hdisk7           1.8       9.2       7.3         19         0
Hdisk8           1.8       9.2       7.3         19         0
Hdisk9           1.8       9.2       7.3         19         0
cd0              0.0       0.0       0.0          0         0

The iostat output shows that one disk is much busier than all of the other disks; therefore, it is important to understand what part of the database is physically stored on Hdisk5.

In this case, the disks are not striped volumes, they are just a bunch of disks (JBOD); therefore, use the operation system tools to determine what file system was created on Hdisk5, then analyze the database to determine what part of the database is stored on that file system.

Step 5: Determine What Is on Hdisk5

The operating system tools indicate that the file system /tablespaces/sample/temp was created on Hdisk5. Based on the name of the file system, it appears to be where the temporary table space was created. This can be verified as follows:

Determine the table space ID for the temporary table space:

select tbspaceid, tbspace from syscat.tablespaces where datatype='T'

The output of the statement above is:

TBSPACEID   TBSPACE
----------- -----------
          1 TEMPSPACE1

1 record(s) selected.

Determine the container definitions for the temporary table space as follows:

list tablespace containers for 1

The output of the statement above is:

Tablespace Containers for Tablespace 1

 Container ID                         = 0
 Name                                 = /tablespaces/sample/temp
 Type                                 = Path

Therefore, the disk with the most activity is the disk where the temporary table space has been placed.

Step 6: Determine and Implement a More Optimal Database Layout

Based on the iostat output, there are 10 physical disks in the server. To eliminate the I/O bottleneck and spread the I/O across as many disks as possible, the physical design of the database needed to be changed. Instead of isolating each of the table spaces to its own physical disk, each table space would be created with eight containers, with one container on each of the disks Hdisk2 through Hdisk9. In this case, because it was an online system, one disk was set aside for the database logs and another for the operating system paging space.

To change the physical layout of the database, an offline backup was taken, the database was dropped, and a redirected restore was performed. During the redirected restore, the table space definitions were changed.

Step 7: Retest

After changing the table space definitions, the response time improved even more, and the desired number of concurrent applications were able to run successfully.

Step 8: Check the System to Ensure Elimination of the I/O Bottleneck

While the applications are running, capture iostat output as follows:

iostat 5 > iostat.out

Next examine the iostat.out file, below:

Disks:        % tm_act     Kbps      tps    Kb_read   Kb_wrtn
Hdisk0           2.6      13.2       7.3         19         0
Hdisk1           4.8      12.2      17.3          0        78
Hdisk2          12.1      29.2      27.2        109       134
Hdisk3          12.5      29.4      27.1        127       125
Hdisk4          12.2      29.1      27.5        113       130
Hdisk5          12.3      29.3      27.4        116       124
Hdisk6          12.4      29.3      27.4        124       126
Hdisk7          12.3      29.1      27.2        103       131
Hdisk8          12.4      29.4      27.3        108       132
Hdisk9          12.2      29.1      27.1        110       130
cd0              0.0       0.0       0.0          0         0

The iostat output now shows that the I/O is spread evenly across the data disks, and none of the disks is busy more than 15% of the time. This leaves room for the I/O subsystem to handle additional requests if needed.



     
    ASPTreeView.com
     
    Evaluation has КЪЧјОЪјИ·Ъexpired.
    Info...