Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Parallelism And Oracle Data Warehousing

Parallel Index Building

* PARALLEL_MIN_SERVERS--The minimum number of query servers that will be active on the instance. System resources are involved in starting a query server, so having the query server started and waiting for requests will speed up processing. Note that if the actual number of required servers is less than the value of PARALLEL_MIN_SERVERS, the idle query servers will be consuming unnecessary overhead, and the value should be decreased.

* PARALLEL_MAX_SERVERS--The maximum number of query servers allowed on the instance. This parameter will prevent Oracle from starting so many query servers that the instance is unable to service all of them properly.

To see how many parallel query servers are busy at any given time, the following query can be issued against the V$PQ_SYSSTAT table:

SELECT * FROM V$PQ_SYSSTAT
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STATISTIC VALUE
----------- ------------
Servers Busy 30

In this case, we see that 30 parallel servers are busy at this moment in time. Do not be misled by this number. Parallel query servers are constantly accepting work or returning to idle status, so it is a good idea to issue the query many times over a one hour period. Only then will you have a realistic measure of how many parallel query servers are being used.

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This is an excerpt from "High Performance Data Warehousing".

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