DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

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Figure 3-47 Explain of the old consistency query 31 Note: We are using a very small catalog, that is why the numbers are so small. But we want to give just an idea on how useful Visual Explain can be for tuning queries. If we click on the top node (1) QUERY, the attributes of the node QUERY appear on the left hand side window informing us that: ► CPU cost (ms): 2 ► CPU cost (SU): 32 ► Cost category: A This information is taken from the table DSN_STATEMNT_TABLE that has been updated by the EXPLAIN statement execution. The CPU cost in milliseconds is the cost in service units divided by the number of service units that the machine where DB2 is running can do in one millisecond. The chart shows that this query has two query blocks. The first query block accesses the table SYSPLAN. If we click the node for table (6) SYSPLAN, the attributes of the table pop up informing us of: ► Table Name: SYSPLAN ► Creator Name: SYSIBM ► Correlation Name: PL ► Cardinality: 61 ► Simple table space The attributes of the node appear on the left hand side of the graph showing as default the information considered for cost estimation: ► Information that appeared in the pop-up + ► Qualifying rows: 14 ► Pages: 61 114 DB2 UDB for z/OS Version 8 Performance Topics
► Timestamp: 2004-11-15 13:44:36.771989 (RUNSTATS) ► Explain time: 2004-11-19 14:56:24:34 If we click the Index node (5) DSNPPH01, the information about the index used to access SYSPLAN pops up: Fullkeycard of 61 and cluster ratio of 0.4918. The attribute side shows the number of leaf pages, number of levels, if the rows are clustered for this index, if the index is padded, and other information. The index scan node (4) shows the number of input RIDs and output RIDs, scanned leaf pages, total filter factor, and number of matching columns for this scan. The fetch node shows a cardinality of 14. This is very interesting. The attribute of the fetch node shows: ► Scanned rows: 61 ► Stage 1 predicate: PL. PLENTRIES=0. Filter factor: 0.459 ► Stage 1 returned rows: 28. If we calculate 61 * 0.459 = 27.999 ► Stage 2 predicate: NOT EXISTS(SELECT 1 FROM SYSDBRM WHERE SYSDBRM.PLNAME=PL.NAME); Filter factor: 0.5. ► Stage 2 returned rows: 14 For each entry in the index DSNPPH01 leaf page (no matching index scan) DB2 has to go to the data portion to verify the predicate PL.PLENTRIES=0. PLENTRIES is the number of package list entries for the plan. The size of the row in SYSPLAN is 3613 bytes in a 4 KB page. Since this query is a correlated subquery, for each row in the outer table the inner query is re-executed. This subquery is an non-matching index-only scan, resulting in many scans to all leaf pages in the index PMSYSDBRM1 because the PLNAME is the second column of the index. So the largest impact comes from the time to scan all leaf pages for the entries in the index for the table SYSDBRM. If the number of DBRMs is small, this can be a few pages, but if the catalog has a large number of DBRMs, for example, 20,000, and the index on columns PLCREATOR, PLNAME, has a key of 16 bytes, resulting in approximately 200 keys per page, there is a total of 100 leaf pages for each plan that has PLENTRIES=0. If there are 10,000 plans not using a package list, there are 10,000 scans of 100 pages. In this example we executed the query under Visual Explain and the output resulted in two rows. Let us take a look at the new Query 3, listed in Table 3-12. Table 3-12 Consistency Query 31 New The new Query SELECT NAME FROM SYSIBM.SYSPLAN WHERE PLENTRIES = 0 AND NAME NOT IN (SELECT PLNAME FROM SYSIBM.SYSDBRM); The new query is a non-correlated query. In a non-correlated subquery case the subquery is executed only once and the result of the query is materialized in the work file. The validation of the clause NOT IN is made in the sorted work file. The optimizer uses the process (scan, sort, work file) to make the performance better as shown in Figure 3-48. This change makes a nice difference when we compare the CPU cost Chapter 3. SQL performance 115
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ibm.com/redbooks Front cover DB2 UD
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Note: Before using this information
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2.5.3 Increased number of deferred
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4.5.2 Conclusion . . . . . . . . .
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7.4.1 ODBC Unicode support . . . .
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x DB2 UDB for z/OS Version 8 Perfor
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3-48 Consistency query - 31 New . .
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xiv DB2 UDB for z/OS Version 8 Perf
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8-5 CF Request Batching - DB2 CPU .
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xviii DB2 UDB for z/OS Version 8 Pe
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Trademarks The following terms are
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Added information The following APA
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► Added reference to June 15, 200
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Michael Parbs is a DB2 Specialist w
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Hugh Smith Jim Teng John Tobler Yoi
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xxx DB2 UDB for z/OS Version 8 Perf
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1.1 Overview 1.1.1 Architecture IBM
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- Column data type changes can be d
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1.1.3 Data warehouse 1.1.4 Performa
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Volatile (or cluster) tables, used
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In this chapter we anticipate the a
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2.1.3 I/O time 2.1.4 Virtual storag
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► The performance benchmarks for
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application that can have great pot
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Because you can significantly incre
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The possible increase in thread foo
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2.5.9 Unicode parser Important: Con
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You can keep the DBRMs in EBCDIC fo
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Macro Parameter Old value New value
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28 DB2 UDB for z/OS Version 8 Perfo
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► Parallel sort enhancement Paral
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Characteristics of the host variabl
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3.1.4 Performance Update 10 rows us
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► Complexity of the fetch. The fi
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► More rows per one SQL statement
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3.2.1 Creating MQTs MQTs compared t
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Special register CURRENT REFRESH AG
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the materialized query table. If it
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Figure 3-9 MQTs and short running q
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► The elapsed time is 22 times sm
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Figure 3-13 Regrouping on MQT resul
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EVE.EXT = 'ADD BILL' AND EVE.TXC =
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Star Schema Figure 3-15 Star schema
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merge joins and work file usage. DB
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Star join access path without a spa
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3.3.4 Performance Sparse index for
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V8 Star Join Access Path Figure 3-2
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Page 128 and 129: FETCH FROM Figure 3-45 FETCH syntax
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Page 142 and 143: 3.14.2 Conclusion Percent reduction
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Page 168 and 169: Important: 4.1.2 Conclusion If you
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RDS OP POOL (MB) N/A RID POOL (MB)
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As you can now appreciate, it is im
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Megabytes A V7 Customer DBM1 Thread
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4.5.1 Performance The most buffer p
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4.6.1 Performance maintained in a 2
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4.6.2 Conclusion We can conclude th
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service for Unicode conversions, an
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overcome this, when DB2 Connect is
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INSERT HV1 1200 HV2 1200 SELECT HV1
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AIX C-program Conversion Routines P
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4.7.1 Performance The improvements
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In October 2003, a new enhancement
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UseServerEncoding data source prope
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4.8.1 Performance 4.8.2 Conclusion
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Multilevel security with row-level
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► The security level that defines
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DB2 must call RACF for this dominan
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4.9.2 Conclusion The CPU increase c
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4.10.1 Performance VSAM does not kn
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4.10.2 Conclusion 4.10.3 Striping A
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5 4 3 2 1 0 9109TLLB 4 Parallel DB2
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--------------------------- -------
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This message is completed with the
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This enhancement is introduced by P
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This record is activated by: -START
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an online transaction with very sim
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216 DB2 UDB for z/OS Version 8 Perf
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5.1 System level point-in-time reco
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BACKUP SYSTEM During backup DB2 rec
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Figure 5-1 FRBACKUP PREPARE elapsed
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Figure 5-4 BACKUP SYSTEM FULL measu
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5.1.2 Conclusion The BACKUP SYSTEM
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Figure 5-7 shows the sliding scale
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Maybe you have implemented a space
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For dynamically prepared queries, D
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► CHAR(8) to VARCHAR(8) ► CHAR(
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Before ALTER INDEX add column, a ta
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30 25 20 15 10 Figure 5-12 FETCH CP
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Percent of index pages Avg. Index L
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300 250 200 time in seconds 150 100
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REORG REBALANCE We executed and mea
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5.4 Volatile table 5.4.1 Conclusion
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If explicit clustering for a table
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Load table of 20M rows, 10 partitio
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Times in seconds 20 18 16 14 12 10
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RUNSTATS INDEX PARTITION of a DPSI
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Note that when the qualified partit
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► “NO” - Values in such colum
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5.6.10 Support for more than 245 se
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6.1 Online CHECK INDEX Online CHECK
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SORTOUT DD UNIT=SYSDA,SPACE=(CYL,(5
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- SORT 6 indexes in parallel - CHEC
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make DB2 take the maximum paralleli
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6.3 LOAD and UNLOAD delimited input
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6.3.2 Conclusion We measured the CP
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Options for cardinality and distrib
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► Number of column groups: 1 ►
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cases is the total time of RUNSTATS
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6.4.5 Conclusion Statistics Advisor
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goals for end-user services. We sho
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alanced across all members. With th
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method. Prior to DB2 V8 those array
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when compared to DB2 V7. At the ser
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7.2.2 Performance - Distributed cli
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Recommendation If you currently do
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► The DB2 Universal JDBC type 4 D
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WebSphere z/OS - DB2 z/OS V8 - Serv
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DB2 Universal Type 4 Driver - JDBC
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Use DB2 Connect when a high amount
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JCC Type 4 Direct 4:3 Concentration
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The SYSIBM.INDOUBT table and the pa
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Batch updates A batched update is a
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Example In DB2 V8 SQL/XML publishin
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INSERT INTO PUB_TAB(DOC) SELECT XML
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7.5.3 Conclusion The new XML publis
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A second role of the managed server
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7.6.3 Performance The following inf
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Impact on coupling facility: You do
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Table 8-1 shows extracts from DB2 P
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and secondary GBP structures have t
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DB2 member already has the table sp
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8.2.1 Performance We ran a number o
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esolve any contention. This extra a
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There is also no need to use RELEAS
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Table 8-12 DB2 I/O CI Limit Removal
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8.5 Miscellaneous items In this sec
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DB2 V8 improves Restart Light. If i
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9.1 Unicode catalog DB2 for z/OS su
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that all applications are converted
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- CLASST: Specifies the threshold a
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From these measurements we observe
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Class 1 CPU time (MSEC) 200 150 100
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dynamic statement cache. If activat
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that everything is ready. This step
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Table Number of rows SYSDATABASE 75
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In Figure 9-7 we describe the perfo
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Old - Query 5 New - Query 5 CPU (se
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Query 35 36 Old DSNTESQ CPU 1 hr 1
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10.1 DB2 Estimator DB2 Estimator V8
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- REAL AND AUXILIARY STORAGE This i
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Another use is during back out of a
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In DB2, the IBM Data Encryption too
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The utilities ran on a G7 Turbo wit
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time Figure 10-1 DB2 HPU vs. UNLOAD
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DSNTIAUL with multi-row fetch The r
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A.1 Maintenance for DB2 V8 The APAR
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APAR # Area Text PTF and Notes PQ88
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APAR # Area Text PTF and Notes PK21
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B.1 DB2 PE Storage Statistics trace
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Storage heading Description 24 BIT
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C.1 DB2 SQL PA additional reports N
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|is the last matching predicate. Ap
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|ANL6052I *** NOTE: | |This index i
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PREDICATE ANALYSIS ----------------
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D.1 DB2 EXPLAIN EXPLAIN describes t
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Table D-2 PLAN_TABLE contents and b
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Column Type Content SORTC_ORDER BY
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Column Type Content OPTHINT CHAR(8)
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D.1.3 DSN_FUNCTION_TABLE You can us
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Example: D-1 Creating DSN_STATEMENT
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Column Type Content BIND_QUALIFIER
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ICF integrated catalog facility ICF
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► DB2 UDB for z/OS V8: Through th
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character set 174 CHECK DATA 262 CH
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Equi-join predicates 54, 402 Equiva
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MINSTOR 145-146 Mismatched data typ
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PQ84160 378, 387 PQ85764 387 PQ8584
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Sort tree nodes 144 SORTDATA 268 SO
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306 Universal Driver for SQLJ and J
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DB2 UDB for z/OS Version 8 Performa
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DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

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