Arina Ielchiieva created DRILL-6442:
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Summary: Adjust Hbase disk cost & row count estimation when filter
push down is applied
Key: DRILL-6442
URL: https://issues.apache.org/jira/browse/DRILL-6442
Project: Apache Drill
Issue Type: Bug
Affects Versions: 1.13.0
Reporter: Arina Ielchiieva
Assignee: Arina Ielchiieva
Fix For: 1.14.0
Disk cost for Hbase scan is calculated based on scan size in bytes.
{noformat}
float diskCost = scanSizeInBytes * ((columns == null || columns.isEmpty()) ? 1
: columns.size() / statsCalculator.getColsPerRow());
{noformat}
Scan size is bytes is estimated using {{TableStatsCalculator}} with the help of
sampling.
When we estimate size for the first time (before applying filter push down),
for sampling we use random rows. When estimating rows after filter push down,
for sampling we use rows that qualify filter condition. It can happen that
average row size can be higher after filter push down
than before. Unfortunately since disk cost depends on these calculations, plan
with filter push down can give higher cost then without it.
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