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From dyozie <...@git.apache.org>
Subject [GitHub] incubator-hawq-docs pull request #59: Feature/best pract
Date Mon, 14 Nov 2016 23:28:34 GMT
Github user dyozie commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq-docs/pull/59#discussion_r87916763
  
    --- Diff: bestpractices/querying_data_bestpractices.html.md.erb ---
    @@ -4,6 +4,23 @@ title: Best Practices for Querying Data
     
     To obtain the best results when querying data in HAWQ, review the best practices described
in this topic.
     
    +## <a id="virtual_seg_performance"></a>Factors Impacting Query Performance
    +
    +The number of virtual segments used for a query directly impacts the query's performance.
The following factors can impact the degree of parallelism of a query:
    +
    +-   **Cost of the query**. Small queries use fewer segments and larger queries use more
segments. Some techniques used in defining resource queues can influence the number of both
virtual segments and general resources allocated to queries. For more information, see [Best
Practices for Using Resource Queues](managing_resources_bestpractices.html#topic_hvd_pls_wv).
    +-   **Available resources at query time**. If more resources are available in the resource
queue, those resources will be used.
    +-   **Hash table and bucket number**. If the query involves only hash-distributed tables,
the query's parallelism is fixed (equal to the hash table bucket number) under the following
conditions: 
    +  	- the bucket number (bucketnum) configured for all the hash tables is the same bucket
number for all tables 
    +   - the table size for random tables is no more than 1.5 times larger than the size
allotted for the hash tables. 
    +
    +  Otherwise, the number of virtual segments depends on the query's cost: hash-distributed
table queries will behave like queries on randomly distributed tables.
    --- End diff --
    
    remote "will" here, and change to "randomly-distributed"


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