Chapter 16

A1: Uncommitted read applications acquire an IN lock on the table but no row-level locks.
A2: The maximum requester I/O block size is 64K.
A3: You can configure DB2 to create some agent processes when DB2 is started by setting the NUM_INITAGENTS parameter to a value greater than zero.
A4: To ensure the integrity of your database, DB2 writes the log buffers to disk when:

  • One or more transactions commit

  • The log buffer is full

  • One second has elapsed since the last log buffer flush

A5: Lock escalation will occur when:

  • The database lock list becomes full

  • Any one application uses more than the MAXLOCKS percent of the lock list

A6: You can capture table and index statistics:

  • By running the runstats utility

  • When loading data into one of your tables

  • By running the reorgchk utility

A7: The reorg command not only reclusters the data in the table, but it also removes embedded free space by deleting rows and eliminating overflow records.
A8: The timestamp monitor switch is enabled by default (it is used by the health monitor).
A9: The reset monitor all command will reset all of the database monitor counters.
A10: You need to create the explain tables to use the Visual Explain tool.
A11: D. The import command cannot capture statistics.
A12: D. The SOFTMAX configuration parameter controls the percentage of a log file that is filled before the page cleaners are triggered to write dirty pages from the buffer pool(s) to disk.
A13: C. When DB2 performs lock escalation, it converts row-level locks to a table-level lock.
A14: B. The configuration parameter sequential detection (SEQ_DETECT) allows DB2 to detect sequential page reads and trigger prefetching.
A15: B and D. The page cleaners are triggered when the percentage of dirty pages in any one buffer pool reaches CHNGPGS_THRESH, or when applications write enough information to the logs to reach SOFTMAX percentage of any log file.
A16: A. reorgchk will indicate if a reorg is suggested based on a number of conditions. One of these conditions is the number of overflow records in the table.
A17: B. An overflow record is created when a row in a table is updated, a varchar column is updated, and its length increases so much that it can no longer fit on the same page.
A18: D. DB2 does not support hints, as they are not needed due to the efficiency of the DB2 optimizer.
A19: D. DTSCAN is not an operator used by DB2.
A20: C. The shared sort heap threshold is a hard limit, and an attempt to start the fourth concurrent shared sort would cause that sort to overflow; therefore, the answer is C.

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