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Wednesday, August 28, 2013

14 design tips for better performance in Datastage

1) Avoid unnecessary type conversions: set the OSH_PRINT_SCHEMAS environment variable to verify that run time schemas match the job design column definitions. If you are using stage variables on a Transformer stage, ensure that their data types match the expected result types.

2) Use Transformer stages sparingly and wisely. Transformer stages can slow down your job. Do not have multiple stages where the functionality could be incorporated into a single stage, and use other stage types to perform simple transformation operations

3) Increase Sort performance where possible. Careful job design can improve the performance of sort operations, both in standalone Sort stages and in on-link sorts specified in the Inputs page Partitioning tab of otherstage types.

4) Remove Unneeded Columns. Remove unneeded columns as early as possible within the job flow. Every additional unused column requires additional buffer memory, which can impact performance and make each row transfer from one stage to the next more expensive. If possible, when reading from databases, use a select list to read just the columns required, rather than the entire table.

5) Avoid reading from sequential files using the Same partitioning method. Unless you have specified more than one source file, this will result in the entire file being read into a single partition, making the entiredownstream flow run sequentially unless you explicitly repartition
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6)It is important to note that the individual SQL statements required by a Sparse Lookup are an expensive operation from a performance perspective. In most cases, it is faster to use a DataStage Join stage between the input and DB2 reference data than it is to perform a Sparse Lookup.

7) For scenarios where the number of input rows is significantly smaller (1:100 or more) than the number of reference rows in a DB2 or Oracle table, a Sparse Lookup may be appropriate. CPU-intensive applications, which typically perform multiple CPUdemanding operations on each record, benefit from the greatest possible parallelism, up to the capacity supported by your system.

8)Parallel jobs with large memory requirements can benefit from parallelism if they act on data that has been partitioned and if the required memory is also divided among partitions.

9)Applications that are disk- or I/O-intensive, such as those that extract data from and load data into RDBMSs, benefit from configurations in which the number of logical nodes equals the number of disk spindles being accessed. For example, if a table is fragmented 16 ways inside a database or if a data set is spread across 16 disk drives, set up a node pool consisting of 16 processing nodes.

10)For some jobs, especially those that are disk-intensive, you must sometimes configure your system to prevent the RDBMS from having either to redistribute load data or to re-partition the data from an extract operation.

11) The speed of communication among stages should be optimized by your configuration. For example, jobs whose stages exchange large amounts of data should be assigned to nodes where stages communicate by either shared memory (in an SMP environment) or a high-speed link (in an MPP environment). The relative placement of jobs whose stages share small amounts of data is less important.

12)Turn off Runtime Column propagation wherever it’s not required.

13) If you are using a copy or a filter stage either immediately after or immediately before a transformer stage, you are reducing the efficiency by using more stages because a transformer does the job of both copy stage as well as a filter stage

14)If you have a single input and single output when you are using a copy stage then set the force option to tru so that DataStage should not try to optimize the job by removing the Copy operation.

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