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From "Zhenhua Wang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SPARK-17074) generate histogram information for column
Date Wed, 19 Oct 2016 03:11:59 GMT

     [ https://issues.apache.org/jira/browse/SPARK-17074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zhenhua Wang updated SPARK-17074:
---------------------------------
    Description: 
We support two kinds of histograms: 
-	Equi-width histogram: We have a fixed width for each column interval in the histogram. 
The height of a histogram represents the frequency for those column values in a specific interval.
 For this kind of histogram, its height varies for different column intervals. We use the
equi-width histogram when the number of distinct values is less than 254.
-	Equi-height histogram: For this histogram, the width of column interval varies.  The heights
of all column intervals are the same.  The equi-height histogram is effective in handling
skewed data distribution. We use the equi- height histogram when the number of distinct values
is equal to or greater than 254.  

We first use [SPARK-18000] and [SPARK-17881] to compute equi-width histograms (for both numeric
and string types) or endpoints of equi-height histograms (for numeric type only). Then, if
we get endpoints of a equi-height histogram, we need to compute ndv's between those endpoints
by [SPARK-17997] to form the equi-height histogram.

This Jira incorporates three Jiras mentioned above to support needed aggregation functions.
We need to resolve them before this one.

  was:
We support two kinds of histograms: 
-	Equi-width histogram: We have a fixed width for each column interval in the histogram. 
The height of a histogram represents the frequency for those column values in a specific interval.
 For this kind of histogram, its height varies for different column intervals. We use the
equi-width histogram when the number of distinct values is less than 254.
-	Equi-height histogram: For this histogram, the width of column interval varies.  The heights
of all column intervals are the same.  The equi-height histogram is effective in handling
skewed data distribution. We use the equi- height histogram when the number of distinct values
is equal to or greater than 254.  



> generate histogram information for column
> -----------------------------------------
>
>                 Key: SPARK-17074
>                 URL: https://issues.apache.org/jira/browse/SPARK-17074
>             Project: Spark
>          Issue Type: Sub-task
>          Components: Optimizer
>    Affects Versions: 2.0.0
>            Reporter: Ron Hu
>
> We support two kinds of histograms: 
> -	Equi-width histogram: We have a fixed width for each column interval in the histogram.
 The height of a histogram represents the frequency for those column values in a specific
interval.  For this kind of histogram, its height varies for different column intervals. We
use the equi-width histogram when the number of distinct values is less than 254.
> -	Equi-height histogram: For this histogram, the width of column interval varies.  The
heights of all column intervals are the same.  The equi-height histogram is effective in handling
skewed data distribution. We use the equi- height histogram when the number of distinct values
is equal to or greater than 254.  
> We first use [SPARK-18000] and [SPARK-17881] to compute equi-width histograms (for both
numeric and string types) or endpoints of equi-height histograms (for numeric type only).
Then, if we get endpoints of a equi-height histogram, we need to compute ndv's between those
endpoints by [SPARK-17997] to form the equi-height histogram.
> This Jira incorporates three Jiras mentioned above to support needed aggregation functions.
We need to resolve them before this one.



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