Correct analysis of 12 difficult issues in DB2 Performance Tuning

Today, we will focus on the comprehensive analysis of 12 difficult problems in DB2 performance tuning, if you are interested in the comprehensive analysis of the 12 Problem Problems in DB2 performance tuning, you can understand the following articles. The following is a detailed description of the main content of the article.

1. Logical design should always be fully mapped to Physical Design

Actual: the physical design in the DB2 database design should be as close as possible to the logical structure, but physical design changes made for performance cannot be ignored because they do not come from the logical design.

2. Put everything in a buffer pool (BP0) for DB2 Management

Actually: As described in the DB2 manual and elsewhere, you have to (10000 4 k pages or less) with very limited memory ), you don't have time to manage it, and you didn't consider performance. It is recommended that you do not place anything except the DB2 catalog and Directory into BP0.

3. DSNDB07 is 100% ordered

Actually: DSNDB07 is never in the 100% order, because there is a random activity on the page in the working file. The activity may be as high as 45%, but usually ranges from 3% to 10%.

4. VARCHAR should always be placed at the end of the row

Actually: This is always a problem. If the table is always read and has very few updates, this will reduce the CPU load, but in other cases, this is the worst, even if the table is compressed. It should be placed at the end only when it is updated frequently, but not usually.

5. The program should be encoded in a way that follows the logical process.

Actual: pseudo code or a logical process diagram does not need to consider performance-related encoding methods. This is very dramatic in the OLTP transaction code.

6. Most processes are not performed in SQL.

Reality: in fact, the opposite is often true. SQL is a rich language that can process most processes. In fact, the biggest difficulty is that SQL is often used as an I/O processor rather than a collection processor.

7. The code and reference table should be used together with the referential integrity (RI) declared by DB2.

Actually, RI should not be used as a shortcut for editing validity. This is usually something else, but should be used in real parent-child relationship.

8. A table can contain at most one or two indexes.

Actual: The table should have multiple indexes according to performance requirements.

9. Non-partitioned indexes (NPI) should not be used, especially in large tables.

Actually: this is related to countless problems, which can be overcome in general, but NPI is necessary for proper access and performance.

10. Large tables should be split

Actually: A table with too much data means performance degradation, which is a legacy concern. This understanding has been eliminated when more than 6 billion rows of data exist in some tables.

11. DB2 is good by default.

Actually: the default version is generally not the best. They are changed based on different versions. For example, bind the CURRENTDATA parameter.

12. Do not use Negation in SQL WHERE predicates.

Actually: Another rule is not clearly explained. Only when the predicate is a negative, the SQL access path may use an unnecessary tablespace scan. However, in most other cases, redundant filtering should be completed in the DB2 engine, which is better.