[
https://issues.apache.org/jira/browse/HIVE-22893?focusedWorklogId=393068&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-393068
]
ASF GitHub Bot logged work on HIVE-22893:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 26/Feb/20 00:09
Start Date: 26/Feb/20 00:09
Worklog Time Spent: 10m
Work Description: jcamachor commented on pull request #915: HIVE-22893
StatEstimate
URL: https://github.com/apache/hive/pull/915#discussion_r384203016
##########
File path: ql/src/java/org/apache/hadoop/hive/ql/udf/UDFSubstr.java
##########
@@ -131,4 +137,52 @@ public BytesWritable evaluate(BytesWritable bw,
IntWritable pos, IntWritable len
public BytesWritable evaluate(BytesWritable bw, IntWritable pos){
return evaluate(bw, pos, maxValue);
}
+
+ @Override
+ public Optional<IStatEstimator> getStatEstimator() {
+ return Optional.of(new SubStrStatEstimator());
+ }
+
+ private static class SubStrStatEstimator implements IStatEstimator {
+
+ @Override
+ public Optional<ColStatistics> estimate(List<ColStatistics> csList) {
+ ColStatistics cs = csList.get(0).clone();
+
+ // this might bad in a skewed case; consider:
+ // 1 row with 1000 long string
+ // 99 rows with 0 length
+ // orig avg is 10
+ // new avg is 5 (if substr(5)) ; but in reality it will stay ~10
+ Optional<Double> start = getRangeWidth(csList.get(1).getRange());
+ Range startRange = csList.get(1).getRange();
+ if (startRange != null && startRange.minValue != null) {
+ double newAvgColLen = cs.getAvgColLen() -
startRange.minValue.doubleValue();
+ if (newAvgColLen > 0) {
+ cs.setAvgColLen(newAvgColLen);
+ }
+
Review comment:
you can remove \n
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Issue Time Tracking
-------------------
Worklog Id: (was: 393068)
> Enhance data size estimation for fields computed by UDFs
> --------------------------------------------------------
>
> Key: HIVE-22893
> URL: https://issues.apache.org/jira/browse/HIVE-22893
> Project: Hive
> Issue Type: Improvement
> Components: Statistics
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
> Labels: pull-request-available
> Attachments: HIVE-22893.01.patch, HIVE-22893.02.patch,
> HIVE-22893.03.patch, HIVE-22893.04.patch, HIVE-22893.05.patch,
> HIVE-22893.06.patch, HIVE-22893.07.patch, HIVE-22893.08.patch,
> HIVE-22893.09.patch, HIVE-22893.10.patch, HIVE-22893.11.patch,
> HIVE-22893.12.patch
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Right now if we have columnstat on a column ; we use that to estimate things
> about the column; - however if an UDF is executed on a column ; the resulting
> column is treated as unknown thing and defaults are assumed.
> An improvement could be to give wide estimation(s) in case of frequently used
> udf.
> For example; consider {{substr(c,1,1)}} ; no matter what the input; the
> output is at most a 1 long string
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