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Administration - Tips & Tricks

A tale of Deep Compression

Thursday, 04 September 2008 15:10 Ravi Khandelwal
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DB2 Row Compression (also known as Deep Compression) is a hot topic of discussion in db2 circles since the release of v9.

Here are some experiences and best practices shared by db2 expert who has worked first hand on planning, implementing and maintaining row compression on a multi-terabyte database. 

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How to remove duplicate rows/date from a table

Thursday, 31 July 2008 14:22 Ravi Khandelwal
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Recently a colleague asked me for a quick way to delete duplicate data from a big table. The problem my colleague faced was that he had to create a new unique index on a table with over million records. There were many duplicates records in the table with respect to this new index and hence his create index command failed.

The quickest and the easiest way I could think was to do the following:
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Quick Command to calculate the DB Size

Tuesday, 22 July 2008 12:10 Ravi Khandelwal
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A quick command to find out the database size is:

db2 "call get_dbsize_info(?,?,?,0)"

GET_DBSIZE_INFO is a stored procedure which calculates the size of the database (used space) and its maximum capacity (allocated space).

The DBSIZE is calculated as:
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Hidden Bufferpools – really, but why?

Tuesday, 15 July 2008 14:31 Ravi Khandelwal
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DB2 has 4 hidden bufferpools in the database which are allocated automatically when a database is activated or started (i.e. first connection to the database).  These are in addition to the default IBMDEFAULTBP and any other user defined bufferpools. These are provided so that an appropriate bufferpool is available in all circumstances and the unavailability of a bufferpool does not cause the system to go down.

There is one hidden buffer pool per page size (4K, 8K, 16K and 32K). These bufferpools are very small in size (16 pages each) and are not present in the system catalogs or the bufferpool system files - thus hidden to the user.  However you can use db2pd to view the hidden bufferpools.
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EXPLAIN tables explained

Monday, 14 July 2008 14:36 Ravi Khandelwal
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EXPLAIN tables capture and hold access plans when the Explain utility is invoked.  You must have these tables created before you can run the explain command.

The script (EXPLAIN.DDL) to create the explain tables is always located in ~sqllib/misc directory of your db2 instance. This script also create a couple of ADVISE tables which are used by the design advisor. The procedure to create the EXPLAIN tables is as follows:
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