vb.net barcode component THE CLUSTERING FACTOR in Java

Painting Code-39 in Java THE CLUSTERING FACTOR

CHAPTER 5 THE CLUSTERING FACTOR
Drawing USS Code 39 In Java
Using Barcode printer for Java Control to generate, create Code 3 of 9 image in Java applications.
www.OnBarcode.com
USS Code 39 Recognizer In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
column argument fails, you may be able to fall back to the sys_op_countchg() technique. In the example, the data is grouped by the clustered column with a group of 9 or 10 blocks calling the sys_op_countchg() function with the value 9 may be the best way of finding an appropriate clustering_factor for your use of that index. Finally, there is the option of just knowing the right answer. If you know that a typical key value will find all its data in (say) 5 table blocks, but Oracle thinks it will have to visit 100 table blocks, then you can simply divide the clustering_factor by 20 to tell Oracle the truth. To find out how many table blocks Oracle thinks it has to visit, simply look at the column user_indexes. avg_data_blocks_per_key, which is simply a restated form of the clustering_factor, calculated as round (clustering_factor / distinct_keys).
Make Code 128C In Java
Using Barcode creation for Java Control to generate, create Code 128B image in Java applications.
www.OnBarcode.com
Generating Code 39 Extended In Java
Using Barcode drawer for Java Control to generate, create Code-39 image in Java applications.
www.OnBarcode.com
Loose Ends
2D Barcode Maker In Java
Using Barcode generation for Java Control to generate, create Matrix Barcode image in Java applications.
www.OnBarcode.com
Draw GTIN - 128 In Java
Using Barcode drawer for Java Control to generate, create UCC-128 image in Java applications.
www.OnBarcode.com
There are many other cases to consider if you want to produce a complete picture of how the clustering_factor can affect the optimizer, and I don t have space to go into them, but here s a thought for the future. Oracle 10g has introduced a mechanism to compact a table online. This only works for a table with row movement enabled that is stored in a tablespace using ASSM. You might use a sequence of commands like the following to compact a table: alter table x enable row movement; alter table x shrink space compact; alter table x shrink space; -- moves rows around -- drops the high water mark
Drawing QR Code 2d Barcode In Java
Using Barcode maker for Java Control to generate, create QR Code image in Java applications.
www.OnBarcode.com
Generate Leitcode In Java
Using Barcode generation for Java Control to generate, create Leitcode image in Java applications.
www.OnBarcode.com
Before you rush into using this feature, just remember that it allows you to reclaim space by filling holes at the start of the table with data moved from the end of the table. In other words, any natural clustering of data based on arrival time could be lost as data is moved one row at a time from one end of the table to the other. Be careful about the effect this could have on the clustering_factor and desirability of the indexes on such a table.
Code 3/9 Generation In Objective-C
Using Barcode generator for iPhone Control to generate, create Code39 image in iPhone applications.
www.OnBarcode.com
Code-39 Decoder In Visual Basic .NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Summary
Making UCC-128 In None
Using Barcode drawer for Excel Control to generate, create GTIN - 128 image in Microsoft Excel applications.
www.OnBarcode.com
Create QR Code In Visual C#.NET
Using Barcode creator for .NET Control to generate, create QR-Code image in .NET framework applications.
www.OnBarcode.com
The clustering_factor is very important for costing index range scans; but there are some features of Oracle, and some performance-related strategies, that result in an unsuitable value for the clustering_factor. In many cases, we can predict the problems that are likely to happen, and use alternative methods for generating a more appropriate clustering_factor. We can always use the dbms_stats package to patch a correct clustering_factor into place. If the clustering_factor is exaggerated because of multiple freelists, or the use of ASSM, then you can use Oracle s internal code for generating the clustering_factor with a modified value for the second parameter of the sys_op_countchg() function to get a more realistic value. If the clustering_factor is exaggerated because of reverse key indexes, added columns, or even column reordering, then you may be able to generate a value based on knowing that the real functionality of the index relies on a subset of the columns. If necessary, build the reduced index on the backup data set, generate the correct clustering_factor, and transfer it to the production index. Adjusting the clustering_factor really isn t hacking or cheating; it is simply ensuring that the optimizer has better information than it can derive (at present) for itself.
Code 128 Code Set B Maker In C#
Using Barcode generator for Visual Studio .NET Control to generate, create USS Code 128 image in VS .NET applications.
www.OnBarcode.com
Make Code-39 In None
Using Barcode drawer for Office Excel Control to generate, create Code39 image in Excel applications.
www.OnBarcode.com
CHAPTER 5 THE CLUSTERING FACTOR
UPC-A Supplement 5 Generation In Objective-C
Using Barcode creation for iPhone Control to generate, create GTIN - 12 image in iPhone applications.
www.OnBarcode.com
PDF-417 2d Barcode Printer In VS .NET
Using Barcode maker for Visual Studio .NET Control to generate, create PDF-417 2d barcode image in .NET applications.
www.OnBarcode.com
Test Cases
PDF-417 2d Barcode Generator In None
Using Barcode drawer for Software Control to generate, create PDF 417 image in Software applications.
www.OnBarcode.com
Generating QR In .NET
Using Barcode drawer for Reporting Service Control to generate, create QR Code image in Reporting Service applications.
www.OnBarcode.com
The files in the download for this chapter are shown in Table 5-3. Table 5-3. 5 Test Cases
Print ANSI/AIM Code 39 In .NET
Using Barcode generator for VS .NET Control to generate, create USS Code 39 image in VS .NET applications.
www.OnBarcode.com
Decoding Barcode In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
www.OnBarcode.com
Script
base_line.sql free_lists.sql reversed_ind.sql reverse.sql assm_test.sql flg.sql col_order.sql extra_col.sql hack_stats.sql clufac_calc.sql setenv.sql
Comments
Script to create the baseline test with freelists set to 1 Repeats the test with freelists set to 5 Repeats the test and then reverses the index SQL to dump a list of numbers sorted by their reversed internal form Repeats the test case in a tablespace set to ASSM Repeats the test with freelists set to two and freelist groups set to three Demonstration of how changing the column order affects the clustering_factor Demonstration of the effects of adding a column to an existing index Script to modify statistics directly on the data dictionary The SQL used by the dbms_stats package to calculate the clustering_factor Sets a standardized environment for SQL*Plus
Copyright © OnBarcode.com . All rights reserved.