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

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Special register CURRENT REFRESH AGE The value in this special register represents a refresh age. The refresh age of an MQT is the timestamp duration between the current timestamp and the timestamp of the last REFRESH TABLE statement for the MQT. This special register controls whether an MQT can be considered in query rewrite as follows: ► Value “0” means no MQTs are considered in query rewrite ► Value “ANY” means all MQTs are considered in rewrite The default value of this special register can be specified in the CURRENT REFRESH AGE field on panel DSNTIP4 at installation time. The data type for CURRENT REFRESH AGE is DEC(20,6). Note: The default value disables query rewrite. Add SET CURRENT REFRESH AGE ANY to make sure of the use of MQT. You can verify this with Explain. Setting the CURRENT REFRESH AGE special register to a value other than zero should be done with caution. Allowing a materialized query table that may not represent the values of the underlying base table to be used to optimize the processing of a query may produce results that do not accurately represent the data in the underlying table. Note: You need to add the new DSNZPARM with REFSHAGE=ANY to enable query rewrite as a default. Special register CURRENT MAINTAINED TABLE TYPES This special register specifies a VARCHAR(255) value. The name of the dynamic ZPARM is MAINTYPE. The value identifies the types of MQT that can be considered in query rewrite: ► Value 'SYSTEM' means all system-maintained, query optimization enabled MQTs ► Value 'USER' means all user-maintained, query optimization enabled MQTs ► Value 'ALL' means all query optimization enabled MQTs The initial value of this special register is determined by the value of field CURRENT MAINT TYPES on installation panel DSNTIP6. The default of this field is SYSTEM. Figure 3-6 shows the relationship between the two special registers for MQTs. CURRENT REFRESH AGE ANY Figure 3-6 Relationship between two special registers for MQTs 42 DB2 UDB for z/OS Version 8 Performance Topics 0 default CURRENT MAINTAINED TABLE TYPES FOR OPTIMIZATION SYSTEM USER ALL NONE All system- maintained query optim ization enabled MQTs All user- maintained query optimization enabled MQTs All query optimization enabled MQTs None None None None None
Rules for query rewrite If the query references tables that are also referenced in MQTs, the optimizer can decide to select the qualified MQT that gives the best performance for the query. Figure 3-7 summarizes the checking that is performed for a query, if automatic query rewrite is generally enabled in your DB2 subsystem at installation time. The automatic query rewrite is supported for dynamically prepared queries that are read-only and have some other restrictions. The automatic query rewrite is a general process that can use a materialized query table M if the fullselect F that makes up the MQT has common source tables as the submitted query Q that is being optimized by DB2. Other conditions are checked during table mapping to verify if the result of the submitted query can be derived from or can directly use the result of one or more materialized query tables. During a predicate matching process, the predicates in the materialized query table fullselect are compared, one by one, to the predicates in the query Q. Diagrammatic Overview of Automatic Query Rewrite Table mapping Common table: table in both Q and F Residual table: table in Q only Extra table: table in F only Rejoin table: common table joins with M to derive non-key columns Predicate matching Join predicates: exact match in both Q and M Local predicates: P in Q subsumes P in M C > 5 subsumes C > 0; C in ('A', 'B') subsumes C in ('A', 'B', 'C') In other words, M contains data that Q needs. Figure 3-7 Rules for query rewrite Table mapping Restrictions on Query Subselect that can be rewritten: Read-only query Contains base tables & table functions, not outer joins only No ROWID, LOB types Heuristics of Selections Match with no regrouping, no residual joins, and no rejoins. Match with no regrouping and no residual joins Match with the largest reduction ratio: |T1|*...*|Tn|/|M|, where T1, ..., Tn are base tables in F Predicate matching Grouping matching Expression derivation Restrictions on Fullselect Base tables & table functions Single SELECT after view and table expression merge No ROWID, LOB types No outer joins . Grouping matching Functional dependency: column K determines C Matching requirement: Grouping column in F determines grouping column in Q No regrouping requirement: Grouping column in Q determines grouping column in F Expression derivation Column equivalence: T1.C1=T2.C1, T2.C1 can be used for T2.C1 Arithmetic expressions: C*(A+B) can be derived from B+A and C Scalar functions: substr(C, 5,10) can be derived from C Set functions: AVG(C) = SUM(C)/COUNT(*) if C NOT NULL VAR(C) = ... Rejoin table columns: From key column T.K derive non-key column T.C If there are any predicates that are in the materialized query table subselect, but are not in the query, then it can be assumed that these predicates may have resulted in discarded rows as the materialized query table was refreshed, and that any rewritten query that makes use of the materialized query table does not give the correct results. The GROUP BY clauses, if any, are compared during grouping matching, to determine if a query GROUP BY clause results in a subset (not necessarily proper) of the rows that are in Chapter 3. SQL performance 43
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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
Page 24 and 25: Added information The following APA
Page 26 and 27: ► Added reference to June 15, 200
Page 28 and 29: Michael Parbs is a DB2 Specialist w
Page 30 and 31: Hugh Smith Jim Teng John Tobler Yoi
Page 32 and 33: xxx DB2 UDB for z/OS Version 8 Perf
Page 34 and 35: 1.1 Overview 1.1.1 Architecture IBM
Page 36 and 37: - Column data type changes can be d
Page 38 and 39: 1.1.3 Data warehouse 1.1.4 Performa
Page 40 and 41: Volatile (or cluster) tables, used
Page 42 and 43: In this chapter we anticipate the a
Page 44 and 45: 2.1.3 I/O time 2.1.4 Virtual storag
Page 46 and 47: ► The performance benchmarks for
Page 48 and 49: application that can have great pot
Page 50 and 51: Because you can significantly incre
Page 52 and 53: The possible increase in thread foo
Page 54 and 55: 2.5.9 Unicode parser Important: Con
Page 56 and 57: You can keep the DBRMs in EBCDIC fo
Page 58 and 59: Macro Parameter Old value New value
Page 60 and 61: 28 DB2 UDB for z/OS Version 8 Perfo
Page 62 and 63: ► Parallel sort enhancement Paral
Page 64 and 65: Characteristics of the host variabl
Page 66 and 67: 3.1.4 Performance Update 10 rows us
Page 68 and 69: ► Complexity of the fetch. The fi
Page 70 and 71: ► More rows per one SQL statement
Page 72 and 73: 3.2.1 Creating MQTs MQTs compared t
Page 76 and 77: the materialized query table. If it
Page 78 and 79: Figure 3-9 MQTs and short running q
Page 80 and 81: ► The elapsed time is 22 times sm
Page 82 and 83: Figure 3-13 Regrouping on MQT resul
Page 84 and 85: EVE.EXT = 'ADD BILL' AND EVE.TXC =
Page 86 and 87: Star Schema Figure 3-15 Star schema
Page 88 and 89: merge joins and work file usage. DB
Page 90 and 91: Star join access path without a spa
Page 92 and 93: 3.3.4 Performance Sparse index for
Page 94 and 95: V8 Star Join Access Path Figure 3-2
Page 96 and 97: 3.3.5 Conclusion Star join workload
Page 98 and 99: . SELECT * FROM PAOLO.TORDER WHERE
Page 100 and 101: But not all mismatched numeric type
Page 102 and 103: V8 shows that PL is joined with CV
Page 104 and 105: Query performance problem Lack of m
Page 106 and 107: 3.5.1 Performance SORTDEVT SYSDA IN
Page 108 and 109: 3.5.2 Conclusions Figure 3-31 Acces
Page 110 and 111: Mismatched data types SELECT COUNT(
Page 112 and 113: 3.7.1 Performance In V8 the paralle
Page 114 and 115: 3.7.2 Conclusions Example 3-9 Multi
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Page 118 and 119: 3.8.3 Conclusion The measurements s
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stores the selected columns from ea
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While there is no optimistic lockin
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FETCH FROM Figure 3-45 FETCH syntax
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► Measurement data collected with
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application has decidedly higher Cl
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Static updatable cursor You can see
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Multi-row FETCH with a static curso
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3.12.5 Conclusion Multi-row FETCH a
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While, for or SELECT ... FROM ...
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3.14.2 Conclusion Percent reduction
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3.15.1 Installation commands. Of co
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Figure 3-47 Explain of the old cons
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in ms = 1 and the CPU cost is 16 se
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Figure 3-50 Suggested RUNSTATS stat
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Looking at the explanation, we can
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The Plug-In Options screen of Stati
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Before the introduction of MQTs, DB
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126 DB2 UDB for z/OS Version 8 Perf
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► Larger VSAM CI sizes: DB2 V8 in
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4.1.1 Performance support caused al
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Regression is about 5% better than
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The results indicate no significant
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Important: 4.1.2 Conclusion If you
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However, the combined impact of oth
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Frees up space below the bar for ot
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from the hiperpools, they were not
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So, we advise you to not overalloca
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See 4.3, “Monitoring DBM1 storage
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Table 4-4 System storage configurat
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Stack 11356 21033 85% 8648 19799 12
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KB 600 500 400 300 200 100 0 Figure
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For the same buffer pool size and o
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4.2.3 Conclusion Nondistributed per
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Important: With PTFs UK04394 (DB2 V
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- DATASPACE BP CONTROL BLOCKS = 0 M
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The EXTENDED REGION SIZE (MAX) is t
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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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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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