The "Dirty" Read (AKA Uncommitted Read) By Craig S. Mullins Anyone accustomed to application programming when access to a database is required understands the potential for concurrency problems. When one application program attempts to read data that is in the process of being changed by another, the DBMS must forbid access until the modification is complete in order to ensure...

DB2 Buffer Pool Essentials (Part 2) By Craig S. Mullins Buffer Pool Page Stealing Algorithm Although most DB2 buffer pools are set up as discussed in the previous section, you can modify the page-stealing algorithm used by DB2 virtual buffer pools using the PGSTEAL parameter. When DB2 removes a page from the buffer pool to make room for a newer...

Using Nulls in DB2 By Craig S. Mullins A null represents missing or unknown information at the column level. If a column “value” can be null, it can mean one of two things: the attribute is not applicable for certain occurrences of the entity, or the attribute applies to all entity occurrences, but the information may not always be known....

Don’t Forget DISPLAY as a Part of Your DB2 Tuning Efforts (Part 1) Although a DB2 performance monitor is probably the best solution for gathering information about your DB2 subsystems and databases, you can gain significant insight into “what is going on out there” using the simple DISPLAY command. The DISPLAY command can be used to return information about the...

UNIX for DBAs (Part 5) System Maintenance Commands The following system maintenance commands will be useful in the UNIX environment for performing such tasks as automatically scheduling tasks, performing backups, and killing processes. The kill command can be used to terminate or discontinue a process that is currently running. Occasionally, an administrator may need to terminate a system process that...

UNIX for DBAs (Part 4) System Status Commands The following commands may be helpful in retrieving system status information while using the UNIX system. The date command is used to display the system date and time. The du command can be used to summarize disk usage information. Sample syntax follows: du name(s) The du command will optionally accept a listing...