2 Setting Up Your Data Warehouse System

Balanced Hardware Configuration

A properly sized and balanced hardware configuration is required to maximize data warehouse performance. The following sections describe important considerations in achieving this balance:

• How Many CPUs and What Clock Speed Do I Need?

• How Much Memory Do I Need?

• How Many Disks Do I Need?

• How Do I Determine Sufficient I/O Bandwidth?

<number of CPUs> = <maximum throughput in MB/s> / 200

<amount of memory in GB> = 2 * <number of CPUs>

Verifying the Data Warehouse Hardware Configuration

Before you install Oracle Database, verify your setup on the hardware and operating-system level. The key point to understand is that if the operating system cannot deliver the performance and throughput you need, Oracle Database will not perform according to your requirements. Two tools for verifying throughput are the dd utility and Orion, an Oracle-supplied tool.

bs=BYTES: Read BYTES bytes at a time; use 1 MB
count=BLOCKS: copy only BLOCKS input blocks
if=FILE: read from FILE; set to your device
of=FILE: write to FILE; set to /dev/null to evaluate read performance; 
  write to disk would erase all existing data!!!
skip=BLOCKS: skip BLOCKS BYTES-sized blocks at start of input

dd bs=1048576 count=200 if=/raw/data_1 of=/dev/null &
dd bs=1048576 count=200 skip=200 if=/raw/data_1 of=/dev/null &
dd bs=1048576 count=200 skip=400 if=/raw/data_1 of=/dev/null &
dd bs=1048576 count=200 skip=600 if=/raw/data_1 of=/dev/null &
dd bs=1048576 count=200 skip=800 if=/raw/data_1 of=/dev/null &
dd bs=1048576 count=200 if=/raw/data_2 of=/dev/null &
dd bs=1048576 count=200 skip=200 if=/raw/data_2 of=/dev/null &
dd bs=1048576 count=200 skip=400 if=/raw/data_2 of=/dev/null &
dd bs=1048576 count=200 skip=600 if=/raw/data_2 of=/dev/null &
dd bs=1048576 count=200 skip=800 if=/raw/data_2 of=/dev/null &

How Should I Set the Memory Management Parameters?

Oracle Database memory has the following components:

• Shared memory: Also called the system global area (SGA), this is the memory used by the Oracle instance.

• Session-based memory: Also called program global area (PGA), this is the memory that is occupied by sessions in the database. It is used to perform database operations, such as sorts and aggregations.

Oracle Database can automatically tune the distribution of the memory components in two memory areas. You have a choice between two mutually exclusive options:

• Set MEMORY_TARGET and MEMORY_MAX_TARGET

• Set SGA_TARGET and PGA_AGGREGATE_TARGET

  If you choose the first option, then you need not set other parameters. The database manages all memory for you. If you choose the second option, then you must specify a size for the SGA and a size for the PGA. The database does the rest.

  The PGA_AGGREGATE_TARGET parameter is the target amount of memory that you want the total PGA across all sessions to use. As a starting point, you can use the following formula to define the PGA_AGGREGATE_TARGET value:

  • PGA_AGGREGATE_TARGET = 3 * SGA_TARGET.

    If you do not have enough physical memory for the PGA_AGGREGATE_TARGET to fit in memory, then reduce PGA_AGGREGATE_TARGET.

• MEMORY_TARGET and MEMORY_MAX_TARGET

  The MEMORY_TARGET parameter enables you to set a target memory size and the related initialization parameter, MEMORY_MAX_TARGET, sets a maximum target memory size. The database then tunes to the target memory size, redistributing memory as needed between the system global area (SGA) and aggregate program global area (PGA). Because the target memory initialization parameter is dynamic, you can change the target memory size at any time without restarting the database. The maximum memory size acts as an upper limit so that you cannot accidentally set the target memory size too high. Because certain SGA components either cannot easily shrink or must remain at a minimum size, the database also prevents you from setting the target memory size too low.

Example: Setting an Initialization Parameter

You can set an initialization parameter by issuing an ALTER SYSTEM statement, as follows:

ALTER SYSTEM SET SGA_TARGET = 1024M;

What Other Initialization Parameter Settings Are Important?

A good starting point for a data warehouse is the data warehouse template database that you can select when you run the Database Configuration Assistant (DBCA). However, any database will be acceptable as long as you ensure you take the following initialization parameters into account:

• COMPATIBLE

  The COMPATIBLE parameter identifies the level of compatibility that the database has with earlier releases. To benefit from the latest features, set the COMPATIBLE parameter to your database release number.

• OPTIMIZER_FEATURES_ENABLE

  To benefit from advanced cost-based optimizer features such as query rewrite, ensure that the OPTIMIZER_FEATURES_ENABLE parameter is set to the value of the current database version.

• DB_BLOCK_SIZE

  The default value of the DB_BLOCK_SIZE parameter is 8 KB, and appropriate for most data warehousing needs. If you intend to use table compression, then consider a larger block size.

• DB_FILE_MULTIBLOCK_READ_COUNT

  The DB_FILE_MULTIBLOCK_READ_COUNT parameter enables reading several database blocks in a single operating-system read call. Because a typical workload on a data warehouse consists of many sequential I/Os, ensure you can take advantage of fewer large I/Os as opposed to many small I/Os. When setting this parameter, take into account the block size and the maximum I/O size of the operating system, and use the following formula:

  DB_FILE_MULTIBLOCK_READ_COUNT * DB_BLOCK_SIZE =
   <maximum operating system I/O size>
  

  Maximum operating-system I/O sizes vary between 64 KB and 1 MB.

• PARALLEL_MAX_SERVERS

  The PARALLEL_MAX_SERVERS parameter sets a resource limit on the maximum number of processes available for parallel execution. Parallel operations need at most twice the number of query server processes as the maximum degree of parallelism (DOP) attributed to any table in the operation.

  Oracle Database sets the PARALLEL_MAX_SERVERS parameter to a default value that is sufficient for most systems. The default value for the PARALLEL_MAX_SERVERS parameter is as follows:

  (CPU_COUNT x PARALLEL_THREADS_PER_CPU x (2 if PGA_AGGREGATE_TARGET > 0; otherwise 1) x 5)
  

  This value might not be enough for parallel queries on tables with higher DOP attributes. Oracle recommends users who expect to run queries of higher DOP to set PARALLEL_MAX_SERVERS as follows:

  2 x DOP x <number_of_concurrent_users>
  

  For example, setting the PARALLEL_MAX_SERVERS parameter to 64 will allow you to run four parallel queries simultaneously, assuming that each query is using two slave sets with a DOP of eight for each set.

  If the hardware system is neither CPU-bound nor I/O bound, then you can increase the number of concurrent parallel execution users on the system by adding more query server processes. When the system becomes CPU-bound or I/O-bound, however, adding more concurrent users becomes detrimental to the overall performance. Careful setting of the PARALLEL_MAX_SERVERS parameter is an effective method of restricting the number of concurrent parallel operations.

• PARALLEL_ADAPTIVE_MULTI_USER

  The PARALLEL_ADAPTIVE_MULTI_USER parameter, which can be TRUE or FALSE, defines whether or not the server will use an algorithm to dynamically determine the degree of parallelism for a particular statement depending on the current workload. To use this feature, set PARALLEL_ADAPTIVE_MULTI_USER to TRUE.

• QUERY_REWRITE_ENABLED

  To take advantage of query rewrite against materialized views, you must set the QUERY_REWRITE_ENABLED parameter to TRUE. This parameter defaults to TRUE.

• QUERY_REWRITE_INTEGRITY

  The default for the QUERY_REWRITE_INTEGRITY parameter is ENFORCED. The database will rewrite queries against only up-to-date materialized views, if it can base itself on enabled and validated primary, unique, and foreign key constraints.

  In TRUSTED mode, the optimizer trusts that the data in the materialized views is current, and the hierarchical relationships declared in dimensions and RELY constraints are correct.

• STAR_TRANSFORMATION_ENABLED

  To take advantage of highly optimized star transformations, set the STAR_TRANSFORMATION_ENABLED parameter to TRUE.

Installing the Oracle Warehouse Builder Demonstration

In subsequent topics, this guide uses exercises from Oracle By Example (OBE) series for Oracle Warehouse Builder to show how to consolidate data from multiple flat file sources, transform the data, and load it into a new relational target.

The exercises and examples are available on Oracle Technology Network (OTN) at http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/10g/r2/owb/owb10gr2_obe_series/owb10g.htm. To help you learn the product, the demonstration provides you with flat file data and scripts that create various Warehouse Builder objects. The OBE pages provide additional information about OWB and the latest information about the exercises.

To perform the Warehouse Builder exercises presented in this guide:

1. Download the demonstration.

   • Go to the location for OWB examples, which is available on OTN from the following location:

     http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/10g/r2/owb/owb10gr2_obe_series/owb10g.htm

   • Click the link for the Oracle By Example (OBE) set for the latest release.

   The demonstration is a set of files in a ZIP archive called owbdemo_files.zip.

   The ZIP archive includes a SQL script, two files in comma-separated values format, and scripts written in Tcl.

2. (Optional) Download the xsales.zip file from the same link, which includes XSALES table data.

3. Edit the script owbdemoinit.tcl.

   The script owbdemoinit.tcl defines and sets variables used by the other tcl scripts. Edit the following variables to match the values in your computer environment:

   • set tempspace TEMP

   • set owbclientpwd workspace_owner

   • set sysuser sys

   • set syspwd pwd

   • set host hostname

   • set port portnumber

   • set service servicename

   • set project owb_project_name

   • set owbclient workspace_owner

   • set sourcedir drive:/newowbdemo

   • set indexspace USERS

   • set dataspace USERS

   • set snapspace USERS

   • set sqlpath drive:/oracle/11.1.0/db_1/BIN

   • set sid servicename

4. Execute the Tcl scripts from the Warehouse Builder scripting utility, OMB Plus.

   For Windows, select Start, Programs, Oracle, Warehouse Builder, and then OMB*Plus.

   For UNIX, locate owb home/owb/bin/unix and then execute OMBPlus.sh

   At the OMB+> prompt, enter the following command to change to the directory that contains the scripts:

   cd drive:\\newowbdemo\\

   Run all of the Tcl scripts in the desired sequence by entering the following command:

   source loadall.tcl

5. Start the Design Center and log in to it as the workspace owner, using the credentials you specified in the script owbdemoinit.tcl.

6. Verify that you successfully set up the Warehouse Builder client to follow the demonstration.

   In the Design Center, expand the Locations node in the Locations Navigator. Expand Databases and then Oracle. The Oracle node includes the following locations:

   OWB_REPOSITORY

   SALES_WH_LOCATION

When you successfully install the Warehouse Builder demonstration, the Design Center displays with an Oracle module named EXPENSE_WH.