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Whether a join criteria satisfied in the table. 3. Whether the table uses sort. 4. All the information about the access path used. 5.
I want to cover my favorite method for generating Explain Plans, and in the process, discuss some of the elements. When EXPLAIN (ONLY) is specified for a BIND or REBIND PACKAGE command, a new package is not generated by Db2; instead, Db2 only generates EXPLAIN information for the package's statements, and it does that as though you had issued EXPLAIN for the individual statements - that is to say, Db2 goes through standard EXPLAIN processing for the package's statements, showing you what the access paths for those statements would be if they were generated right now. RBA is a hexa decimal number and DB2 will create it based on some timestamp. If we Quiesce on a tablespace, DB2 will put a enry in SYSCOPY with the RBA and a entry in DB2 directory. so that they will be used as recovery points if needed.
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Configuration Parameters 8. Explain Snapshot Visual Explain This tutorial contains lessons on: v Creating explain snapshots. These are requirements for displaying access plan graphs.
DB2 will automatically use the SYSTOOLS explain tables if they do not exist under your userid. Similarly, if AQT finds the explain tables under your userid, it will use them in the explain displays. DB2 Visual Explain DB2 提供了非常直观有效的方法来查看查询的存取计划。DB2 Visual Explain 能够获得可视化的查询计划，而 db2expln 命令则可以获得文本形式的查询计划。有了查询计划，我们就可以有针对的对查询进行优化。
The previous sections used the explain tool to examine DB2 access plans. The next sections will introduce the db2exfmt tool and discuss how to interpret its output. The db2exfmt tool reads the explain tables and builds an ASCII report with the explain information, as well as a graphical representation of the access plan. 2013-06-04 · The DB2 Optimizer is a cost-based optimizer, which means it calculates the cost of multiple access paths (in a unit called Timerons), and then chooses the cheapest access path. One of the advantages of the SQL language is that it means we don’t have to know where a particular piece of data lives on disk or memory.
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The Explain command details the access path defined by DB2 and allows you to analyze how the data will be accessed and how you can improve the command’s performance. db2 CONNECT TO database-name db2 CALL SYSPROC.SYSINSTALLOBJECTS ('EXPLAIN', 'C', CAST (NULL AS VARCHAR (128)), CAST (NULL AS VARCHAR (128))) This call creates the explain tables under the SYSTOOLS schema. To create them under a different schema, specify a schema name as the last parameter in the call. Run the EXPLAIN.DDL command file: You can use the DB2 EXPLAIN statement to determine the access paths for the SELECT parts of your statements. DB2 EXPLAIN helps you answer questions about Query Performance & Query Optimization; the answers give you the information that you need to make performance improvements.
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Explain Snapshot Visual Explain This tutorial contains lessons on: v Creating explain snapshots. These are requirements for displaying access plan graphs. I installed IBM - DB2 Express Server Edition and I'm trying to run an EXPLAIN statement on a query.
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2. Whether a join criteria satisfied in the table. 3. Whether the table uses sort. 4.
If the user has DBADM authority, or the database registry variable DB2_VIEW_REOPT_VALUES is set to YES, the EXPLAIN_PREDICATE table will also be populated with the values if they are used to reoptimize the statement. What you're looking for is covered by two DB2 utilities: The explain utility, which shows the optimizer's access plan and estimated cost for a specific query (based on current RUNSTATS statistics) The design advisor, which recommends structural changes to improve the performance of one or more queries.