Cooling Your Overloaded Database with New DB2 UDB EEE Partitions


Marin Komadina

Today the server hardware is so powerful that it is not unusual to
find standalone low cost SMP (Symmetric Multiprocessing Machine) servers in
different clustered and non-clustered configurations. Data volume and the
number of concurrent database connections on those systems are rising higher
and higher. When we approach warning levels in our hardware utilization
we can simply expand the system with more hardware resources (disk space,
processors, memory) and new DB2 UDB EEE database partitions.

This article covers:

  • DB2
    UDB EEE Terminology

  • Partitioned
    Database Design Consideration

  • Existing
    Database Configuration Inventory

  • Procedure
    for Adding New Database Partition

  • Future
    Enhancements

DB2 UDB EEE Terminology

Database Instance is a database manager logical environment consisting of
several database engine processes and their memory allocations. A database is
created within a database instance.

Node is a physical or logical machine hosting one or more DB2
UDB EEE instances or partitions.

Database Partition is a logical database unit with private data and index
subsets, configuration files and transaction logs. Database partitions can be
configured to support Intra-partition (SQL query broken in smaller parts and
executed in parallel on single partition), and inter-partition parallelism (SQL
query executed in parallel on several partitions), or both of them.

  • Catalog partition is the main database partition which is running DB2
    UDB EEE instance manager. This partition has the number 0 and holds the DB2 UDB
    EEE system tables that are not distributed to any other partition.

  • Coordinator partition (dispatcher) is a partition
    that coordinates query execution, sends query parts on other partitions for
    execution, assembles the result data set and returns it to the requester.

Node
group
is a named
set of one or more database partitions that belong to the same database. Node
group provide logical layer between tablespaces and partitions.

Partitioned Database Design Consideration

  • Hardware Configuration

    Partition design depends on the underlying hardware
    configuration. In physical partition design, we have separate partitions on
    separate hosts connected together with high-speed links. Today a logical
    partition design, where we have several standalone n-CPU machines with a large amount
    of RAM and several database partitions running on the same physical host, is
    often used. In this configuration, every partition has exclusive access to its
    own disk and memory. CPU resources are shared between partitions.

  • DB2 UDB EEE
    failover design

    The failover function is strictly dependent on underlying
    cluster software such as IBM HACMP (High Availability Cluster Multi-Processing),
    Veritas Cluster Server, Sun Cluster, and Microsoft Cluster Server. The main
    consideration in failover design is the proper distribution of data from the
    failed partition to all others after failover. Cluster software is unaware of
    partitioning schema inside the database. The default behavior of just switching
    the database partition from one node to another would create an unbalanced
    database configuration, with one or more overloaded nodes. For that reason we
    must configure the cluster software with a takeover list and DB2 UDB EEE with
    multiple partitions per node so that each surviving node takes over the same amount of data.

  • Recommended Data Volume per Partition

    For
    the best performance, it is recommended to hold to a maximum of 50-100 GB of user
    data per partition.

  • CPU Number Per Partition

    This is the optimal performance that we can get with 2 CPUs per
    partition.

  • Partitions Number Per Table

    The number of partitions per user table varies and is dependant on
    table size. The largest table should span all partitions while small tables
    should be partitioned using the join key as a partition key. Small tables should
    be grouped together on catalog node.

  • Buffer Pool Configuration

    The buffer
    pool configuration depends on the tablespace(s) page size. For every page size
    that differs from the default (4KB), we have to calculate and create a new
    buffer pool for that tablesapce(s).

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