Databases Reference
In-Depth Information
The net result is a very active DB2 table with extremely high log rates.
Using the IBM guideline that DB2 logs should be sized at 90% of a 3480 car-
tridge, the bank found that, if it adhered to this rule of thumb without doing
something about the amount of log data that it was creating, log files would
have to be changed about every 10 minutes. In other words, the bank
would be trying to spin off a 3480 cartridge every 10 minutes — not a very
tenable situation.
Based on the recommendation of a consulting firm that was designing
the bank's DB2 environment, the bank installed SAMS:Compress for DB2,
the Sterling Software data compression system for DB2 tables. The result of
compressing that single DB2 table was a 75% reduction in DB2 log volume
and a fivefold decrease in tape consumption for archiving. More important,
the bank achieved significant improvements in performance and opera-
tional throughput, in addition to DASD savings.
SAMS:Compress for DB2 automatically compresses and restores data
being written to or read from a DB2 table to conserve DASD space. The
product allows users to select both the DB2 tables for compression and the
compression technique, balancing the benefits of substantial storage
space savings against CPU overhead requirements. An integral compres-
sion analysis utility helps users select the optimal compression technique
for their DB2 tables.
DASD COMPRESSION
The storage facility commonly found in the IBM mainframe and midrange
environments is DASD. Although originated by IBM, there are several third-
party suppliers as well. In essence, DASD provides consistently fast access
to data, regardless of its specific location in massive databases. Typically,
the available storage space is allocated to specific applications so that fre-
quently used information is made immediately available. Less frequently
used information is stored on less-expensive archival media. In a document-
imaging application, for example, active documents in electronic file folders
would be stored on DASD for quick retrieval, while inactive files or folders
may be stored on magnetic tape. Those that are considered closed would be
permanently archived to tape or optical media.
Organizations using DASD also most likely use the popular IBM DB2, a
family of relational database products that is used for decision support,
transaction processing, and an extensive range of business applications.
The DB2 family spans AS/400 systems, RISC System/6000 hardware, IBM
mainframes, non-IBM machines from Hewlett-Packard and Sun Microsys-
tems, and operating systems such as OS/2, Windows (95 and NT), AIX, HP-
UX, SINIX, SCO OpenServer, and the Solaris Operating Environment. In fact,
DB2 is the backbone database server in many of the largest corporation in
the world, handling over 7.7 billion transactions worldwide every day.
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