why dba needed in dwh projects

WHY DBA IS NEEDED IN ORACLE DWH PROJECTS?

By Anurag Vidyarthi (Accenture,Norway)

Main feature of DWH projects Partitioning Parallelism Compression Materialized Views Demand for Performance Scalability ETL Job Analysis Proactive Co-ordination Capacity Planning

Partitioning

Why a specific table should be partitioned ?

Which kind of indexes are best on any specific partition table ?

Actual explain plan is taking advantage of partitioning pruning ?

Role of partition maintenance operation in ETL?

Parallelism

Is system/sesion/Query is utilizing the parallelism for better performance.

Balancing the utilization of parallel resource.

Monitoring the parallel resource utilization.

Enabling/disabling parallelism on selected objects for specific purposes. In specific sessions.

Compression

Which tables are suitable for compressing.

Compression scope – whole table or selected partition.

Uncompression for specific purposes. Analysing the performance/space

because of compression.

Materialized Views(MVs)

Analyzing the SQLs and suggest if MV creation can help in better performance.

Query rewite implementation. MVs refresh

Suitable Methods Performance

Indexing/partitioning of MVs

Demand for Performance scalability

Finding which SQLs suddenly behave abnormally and finding Rogue SQLs whose SQL plan changed because of data involved.

ETL job analysis from database-side. Finding Why same ETL Job one day takes

4-5 minutes and another day takes hours: Index rebuilding Truncate table statement is time consuming. MV refreshes are time consuming.

Demand for Performance scalability

Execution plans which don't fit with the partitioning strategy can run worse than they did against the unpartitioned table.

What type of Index should be created to enhance the query performance ? Global vs Local Bitmap vs B-tree

Full table might be better for performance in certain cases.

Typical Question :Query is taking

time As for reducing the cost, it's a bit difficult

to offer advice on every query: queries take time, and queries which use a lot of data take longer.

Secret ? The secret of tuning is to understand what is a reasonable amount of time for a given query. Cost is irrelevant if the query runs fast enough.

Miscellaneous DBA Tasks Running AWR\ADDM and analyzing candidates

for improvements like alternate explain-plan. Reducing unnessesary IO Implementing resource usage for better

utilization of resources. Finding why Index is not used in any SQL(s). Finding suitable columns for indexing. RAM monitoring and on-demand stats

gathering Tracing of erratic session. Registering and Handling of Oracle Service

requests.

ETL Job Analysis Most ETL tools like powercenter and OWB

has repositores stored in Oracle database. Easy monitoring of ETL jobs using the

repository tables and views. Rescheduling of ETL jobs based upon :

Resource consumption Dependency

Pro-active co-ordination

Example Business Requirement :

Business Users want to run critical queries on a large table that involves FTSs.To reduce the query response times parallel query is utilized. Running one of these queries utilizes 75% of all system resources on the machine for a minute.The business requirements determine that over 200 users need to perform this query each once about every 2 minutes.

Issue :

This sort of problem probably cannot be solved by any machine. In this example it is possible to see where a well informed set of system designers can ensure they do not commit to deliver a business requirement that is clearly impossible to deliver.

Possible Solution :

A proactive DBA may notice that all these queries could be satisfied by a simple summary table. In this case the business requirements could be satisfied with ease. In essence it takes more than just raw machine horsepower to solve DWH problems and in fact a proactive entrepreneurial approach is what is really required.

Capacity Planning

Logical DB access planning (user,tablespace)

Data Modeling for performance Star schema

Resource Requirements and Scaleabilty.

Data growth prognosis.

Thanks

Questions ???