This report contains a summary of the recommendations from the Query Tuner advisors and tools. Examine the recommendations and corresponding DDL scripts, if applicable, and take appropriate actions to tune your query. You can also examine the formatted query and access plan summary, and cross reference the recommendations generated by the advisors. Use the cataloged table, column, and index information to do further analysis and tuning. Navigate to the different sections using the action buttons and then return to the top of the report using Back to top.
Advice Number | Advice Type | Tuning Recommendation Description |
---|---|---|
1 | Statistics | CRITICAL: Consolidate statistics: Use RUNSTATS to recollect all the relevant statistics for this query for an accurate evaluation Important: if statistics are missing, Query tuner estimates subsequent recommendations based on database default statistics. Click here to review the recommended RUNSTATS script. |
2 | Index | Index recommendation is found for the following tables: TPCDS .CATALOG_RETURNS. The total estimated disk space required is 2.493 MB and the estimated performance improvement is 92.258%. This index recommendation will help improve query performance for general indexing. Click here to review the recommended CREATE INDEX DDL script. |
3 | Query | Provide a predicate on column R_ITEM_SK. Consider adding the following predicate to column R_ITEM_SK in table REPAIR: R_ITEM_SK IS NOT NULL to filter the table earlier and unlock more possible join sequences.Click here to see the affected query text. |
4 | Access path | Avoid table space scan (Operator ID = 6) on table TPCDS.CATALOG_RETURNS.
The table is accessed by a table space scan (table scan). When a large number of records are returned, DB2 might be using an inefficient access path. Consider running the statistics advisor or running the index advisor to determine whether creating an index might improve the access path.Click here to see the access plan operator. This Access path recommendation also applies to the following objects. |
5 | - TPCDS.REPAIR, (Operator ID = 7) |
The tuning advisors recommend the following actions to update the table and index statistics, and to create the necessary indexes to improve the query performance. Update Statistics StatementsRecommended Action
Advice Number | Statement Number | Statement Text |
---|---|---|
1 | 1 | RUNSTATS ON TABLE "TPCDS"."REPAIR" ON COLUMNS ( "R_DIAGNOSIS" LIKE STATISTICS ) WITH DISTRIBUTION ON COLUMNS ( "R_ORDER_NUMBER" NUM_FREQVALUES 15 NUM_QUANTILES 25 , "R_ITEM_SK" NUM_FREQVALUES 15 NUM_QUANTILES 25 ) AND SAMPLED DETAILED INDEXES ALL ALLOW WRITE ACCESS |
1 | 2 | RUNSTATS ON TABLE "TPCDS"."CATALOG_RETURNS" WITH DISTRIBUTION ON COLUMNS ( "CR_ORDER_NUMBER" NUM_FREQVALUES 15 NUM_QUANTILES 25 , "CR_ITEM_SK" NUM_FREQVALUES 15 NUM_QUANTILES 25 , "CR_RETURN_SHIP_COST" NUM_FREQVALUES 15 NUM_QUANTILES 25 ) AND SAMPLED DETAILED INDEXES ALL ALLOW WRITE ACCESS |
Create Index Statements
Estimated performance improvement is 92.258%.Advice Number | Statement Number | Statement Text |
---|---|---|
2 | 1 | CREATE UNIQUE INDEX "DB2OE "."IDX908271915160000" ON "TPCDS "."CATALOG_RETURNS" ("CR_ORDER_NUMBER" ASC, "CR_ITEM_SK" ASC) INCLUDE ("CR_RETURN_SHIP_COST") ALLOW REVERSE SCANS |
Input Query
WITH DT( COST | ||
) | ||
AS ( | ||
SELECT CASE WHEN R.R_REPAIR_COST < 100.0 | ||
THEN 'small' | ||
WHEN R.R_REPAIR_COST < 1000.0 | ||
THEN 'medium' | ||
ELSE 'expensive' | ||
END | ||
FROM TPCDS.REPAIR AS R | /* no. of rows=10000 */ | |
, TPCDS.CATALOG_RETURNS AS C | /* no. of rows=144222 */ | |
WHERE C.CR_RETURN_SHIP_COST > 100 | ||
AND R.R_DIAGNOSIS LIKE '%fire%' | ||
AND R.R_ORDER_NUMBER > 10 | ||
AND R.R_ORDER_NUMBER = C.CR_ORDER_NUMBER | ||
AND R.R_ITEM_SK = C.CR_ITEM_SK | /* WARNING=Advice #3 */ | |
) | ||
SELECT DT.COST | ||
, COUNT(*) | ||
FROM DT | ||
GROUP BY DT.COST |
Subselect (QBLOCK) | Estimated Return Rows | Estimated Cost | Plan Operator Totals | Explain Timestamp | Cataloged Tables Referenced | Catalog Index Usage | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Total Cost | Total CPU | Total IO | Table Scan | Index Scan | Join | Sort | Predicate | Used Indexes (%) | Unused Indexes (%) | Existing Indexes | ||||
- | 66.076 | 9,842.858 | 512,655,328.000 | 5,306.000 | 2 | 0 | 1 | 1 | 6 | 2009-08-27T12:13:32 | 2 | 0 (0.0%) | 3 (100.0%) | 3 |
Database server transformed query for access plan
SELECT Q4.$C0 AS "COST", Q4.$C1 FROM (SELECT Q3.$C0, COUNT(* ) FROM (SELECT CASE WHEN (Q1.R_REPAIR_COST < +100.0) THEN 'small' WHEN (Q1.R_REPAIR_COST < +1000.0) THEN 'medium' ELSE 'expensive' END FROM TPCDS.REPAIR AS Q1, TPCDS.CATALOG_RETURNS AS Q2 WHERE (Q1.R_ORDER_NUMBER = Q2.CR_ORDER_NUMBER) AND (Q1.R_ITEM_SK = Q2.CR_ITEM_SK) AND (Q1.R_DIAGNOSIS LIKE '%fire%') AND (100 < Q2.CR_RETURN_SHIP_COST) AND (10 < Q1.R_ORDER_NUMBER)) AS Q3 GROUP BY Q3.$C0) AS Q4 |
Predicate for Table Access and Join
Predicates can disqualify rows and reduce the amount of required processing at later stage. The earlier DB2 can evaluate a predicate, the more the query performance can improve. When possible, try to write queries that evaluate the most restrictive predicates first. When predicates with a high filter factor are processed first, unnecessary rows are disqualified as early as possible, which can reduce processing cost at a later stage. Filter factors affect the choice of access paths by estimating the number of rows that qualified by a set of predicates.Query Block: Plan Identifier* | Predicate Identifier | Predicate Text | Used in Join | Used in Index Scan | Used in Table Scan | Filter Factor |
---|---|---|---|---|---|---|
- | 3 | (10 < Q2.CR_ORDER_NUMBER) | No | No | Yes | 0.999966 |
- | 4 | (Q1.R_ORDER_NUMBER = Q2.CR_ORDER_NUMBER) | Yes | No | No | 0.000011 |
- | 5 | (Q1.R_ITEM_SK = Q2.CR_ITEM_SK) | Yes | No | No | 0.000056 |
- | 6 | (Q1.R_DIAGNOSIS LIKE '%fire%') | No | No | Yes | 0.100000 |
- | 7 | (100 < Q2.CR_RETURN_SHIP_COST) | No | No | Yes | 0.660957 |
- | 8 | (10 < Q1.R_ORDER_NUMBER) | No | No | Yes | 0.999700 |
Operator Identifier** | Table Name (Correlation ID) | Index Access | Estimated Qualified Rows | Cumulative Total Cost | Cumulative CPU Cost | Cumulative IO Cost | Predicate ID (How is applied) | Advice Number |
---|---|---|---|---|---|---|---|---|
6 | TPCDS.CATALOG_RETURNS (Q2) |
- | 95,321.289 | 9,629.491 | 459,063,968.000 | 5,155.000 | 4 | |
7 | TPCDS.REPAIR (Q1) |
- | 999.700 | 182.229 | 26,591,966.000 | 151.000 | 5 |
Join Identifier** | Join Left Operand | Join Right Operand | Join Method | Is Join Data Sorted | Estimated Qualified Rows | Cumulative Total Cost | Cumulative CPU Cost | Cumulative IO Cost | Predicate Identifier | Advice Number |
---|---|---|---|---|---|---|---|---|---|---|
5 | TPCDS.CATALOG_RETURNS (Correlation ID=Q2) |
TPCDS.REPAIR (Correlation ID=Q1) |
HSJOIN | No | 660.759 | 9,841.513 | 511,488,480.000 | 5,306.000 | 4, 5 | 5 |
Method for applying the predicate.
The following list displays the referenced table statistics in the query access plan. All columns and indexes for the referenced tables are also listed. You can examine the table size, associated primary and foreign keys, cardinality and index columns information; and use the table and index statistics to plan for and reorganize tables and indexes with the REORG utility.
There are 2 referenced tables, 0 used indexes (0.0%), 3 unused indexes (100.0%), and a total of 3 indexes.
Referenced tables, sorted by table name.
**Tablespace name, qualified with database name when on a DB2 for z/OS data server.Table Name | Tablespace Name | Foreign Key -> Parent Key | Number of Columns | Table Cardinality | Number of Pages | Average Row Size | Stats Last Updated |
---|---|---|---|---|---|---|---|
TPCDS.CATALOG_RETURNS | USERSPACE1 |
|
27 | 144,222 | 5,154 | 143 | 2009-08-19T12:45:13 |
TPCDS.REPAIR | TS00001 |
|
8 | 10,000 | 150 | 60 | 2009-08-19T12:45:12 |
All table columns, sorted by table name and physical column order
Table Name | Column Number | Column Name | Column Type | Length | Nullable | Column Cardinality |
---|---|---|---|---|---|---|
TPCDS.CATALOG_RETURNS | 0 | CR_RETURNED_DATE_SK | INTEGER | 4 | Y | 2069.0 |
1 | CR_RETURNED_TIME_SK | INTEGER | 4 | Y | 70656.0 | |
2 | CR_ITEM_SK | INTEGER | 4 | N | 17856.0 | |
3 | CR_REFUNDED_CUSTOMER_SK | INTEGER | 4 | Y | 57857.0 | |
4 | CR_REFUNDED_CDEMO_SK | INTEGER | 4 | Y | 96257.0 | |
5 | CR_REFUNDED_HDEMO_SK | INTEGER | 4 | Y | 7169.0 | |
6 | CR_REFUNDED_ADDR_SK | INTEGER | 4 | Y | 45057.0 | |
7 | CR_RETURNING_CUSTOMER_SK | INTEGER | 4 | Y | 76801.0 | |
8 | CR_RETURNING_CDEMO_SK | INTEGER | 4 | Y | 144222.0 | |
9 | CR_RETURNING_HDEMO_SK | INTEGER | 4 | Y | 7169.0 | |
10 | CR_RETURNING_ADDR_SK | INTEGER | 4 | Y | 47105.0 | |
11 | CR_CALL_CENTER_SK | INTEGER | 4 | Y | 7.0 | |
12 | CR_CATALOG_PAGE_SK | INTEGER | 4 | Y | 7297.0 | |
13 | CR_SHIP_MODE_SK | INTEGER | 4 | Y | 21.0 | |
14 | CR_WAREHOUSE_SK | INTEGER | 4 | Y | 6.0 | |
15 | CR_REASON_SK | INTEGER | 4 | Y | 36.0 | |
16 | CR_ORDER_NUMBER | INTEGER | 4 | N | 94208.0 | |
17 | CR_RETURN_QUANTITY | INTEGER | 4 | Y | 101.0 | |
18 | CR_RETURN_AMOUNT | DECIMAL | (7,2) | Y | 76801.0 | |
19 | CR_RETURN_TAX | DECIMAL | (7,2) | Y | 26113.0 | |
20 | CR_RETURN_AMT_INC_TAX | DECIMAL | (7,2) | Y | 92161.0 | |
21 | CR_FEE | DECIMAL | (7,2) | Y | 10369.0 | |
22 | CR_RETURN_SHIP_COST | DECIMAL | (7,2) | Y | 62465.0 | |
23 | CR_REFUNDED_CASH | DECIMAL | (7,2) | Y | 66561.0 | |
24 | CR_REVERSED_CHARGE | DECIMAL | (7,2) | Y | 56833.0 | |
25 | CR_STORE_CREDIT | DECIMAL | (7,2) | Y | 54273.0 | |
26 | CR_NET_LOSS | DECIMAL | (7,2) | Y | 93185.0 | |
TPCDS.REPAIR | 0 | R_REPAIR_TICKET_SK | INTEGER | 4 | N | 10000.0 |
1 | R_ITEM_SK | INTEGER | 4 | Y | 5988.0 | |
2 | R_ORDER_NUMBER | INTEGER | 4 | Y | 6976.0 | |
3 | R_CALL_CENTER_SK | INTEGER | 4 | Y | -1.0 | |
4 | R_REPAIR_CUSTOMER_SK | INTEGER | 4 | Y | -1.0 | |
5 | R_REPAIR_ADDR_SK | INTEGER | 4 | Y | -1.0 | |
6 | R_REPAIR_COST | DECIMAL | (7,2) | Y | -1.0 | |
7 | R_DIAGNOSIS | VARCHAR | 3,000 | Y | 1.0 |
All indexes, sorted by table name, referenced index name, unreferenced index name, and key column sequence
Table Name | Index Name | Index Type | Unique Rule | Used in Plan | Leaf Pages | Index Levels | Cluster Ratio (%) | Clustering | First Key Cardinality | Full Key Cardinality | Key Column | Key Order | Column Cardinality | Statistics Last Updated |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
TPCDS.CATALOG_RETURNS | SYSIBM.SQL090429132203100 | Regular | Primary index | No | 764 | 3 | -1 | No | 17,856.000 | 144,222.000 | CR_ITEM_SK | Asc | 17856.0 | 2009-08-19T12:45:13 |
CR_ORDER_NUMBER | Asc | 94208.0 | 2009-08-19T12:45:13 | |||||||||||
TPCDS.REPAIR | DB2OE.IDX904072054270000 | Regular | Duplicate allowed | No | 59 | 2 | -1 | No | 5,988.000 | 9,998.000 | R_ITEM_SK | Asc | 5988.0 | 2009-08-19T12:45:12 |
R_REPAIR_COST | Asc | -1.0 | 2009-08-19T12:45:12 | |||||||||||
SYSIBM.SQL090403183259280 | Regular | Primary index | No | 42 | 2 | -1 | No | 10,000.000 | 10,000.000 | R_REPAIR_TICKET_SK | Asc | 10000.0 | 2009-08-19T12:45:12 |
The following log records the runtime information including the client version, server license, and which tuning advisors are used to obtain query tuning recommendations.
Server license entitlement and version: IBM Optim Query Workload Tuner for DB2, Version 2.2
Query Tuner client version: 2.2.0.1
Report completion timestamp: 2009-08-27T12:14:24.
Advisor | Run Status |
---|---|
Statistics | Success |
Index | Success |
Query | Success |
Access path | Success |