IBM eserver i5 Handbook page 561

Draft Document for Review October 18, 2004
record access of the current block can then be performed locally at the client
without accessing the server. This ability is provided for all isolation levels.
Parallel data access
Queries returning or requiring DB2 UDB for iSeries to process large amounts
of data require significant input/output (I/O) activity. Due to the iSeries'
single-level store architecture, this data is often spread across many physical
devices. The parallel data access feature allows multiple internal DB2 UDB
for iSeries tasks to be activated for each physical device, allowing DB2 UDB
for iSeries to transfer data from disk to memory faster than with the previous
single task I/O architecture.
Query Governor
Long-running queries can have negative performance effects for other users
of a database, so that a single query can consume an unusually large amount
of resources, which negatively affects the performance of other users.
The governor facility allows a time limit to be set for a query. Before the query
is started, its run time is estimated. If the estimate exceeds the specified time
limit, the query is not started. This is advantageous over similar functions on
other databases that let the query run for a portion of time and then stop it
since no unnecessary processing of the query occurs.
Query tuning
DB2 UDB for iSeries provides both iSeries Navigator graphical and
programmatical CL command interfaces to help tune SQL queries. Users can
dynamically control how DB2 UDB for iSeries is to optimize queries by
changing a set of query attributes (such as the parallel degree characteristic).
Both summary and detailed database performance monitors can be used to
track and analyze SQL statement performance. A Visual Explain capability
can be used to graphically show how a specific query has been optimized and
can suggest indexes that may help performance.
Scalability
DB2 UDB for iSeries supports very large database environments. A single
table can be up to one TB and 4.2 billion rows. Distributed tables can be up to
32 TB.
DB2 Symmetric Multiprocessing (SMP) for iSeries and DB2 Multisystem
support enable both horizontal and vertical growth.
Ease of use and management
The iSeries' reputation for usability and maintainability is unsurpassed in the
industry. This is due in part to the tight integration of i5/OS or OS/400 and DB2
UDB for iSeries. Users do not have to learn separate operating system and
database functions, nor are they burdened with maintaining the complex
i5/OS and OS/400 (5722-SS1): Architecture
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