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https://issues.apache.org/jira/browse/PHOENIX-2724?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Samarth Jain updated PHOENIX-2724:
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Attachment: PHOENIX-2724_v2.patch
Thanks for the review [~jamestaylor] and [~ankit.singhal].
We can't use SerialIterators any more if the tables are salted or local indexes
and a row key order is requested. This is because we need to be able to do a
merge sort between all the scanners which isn't possible now when we are using
SerialIterators.
This also brings up an interesting question - what should we do if the user has
explicitly requested serial execution via a hint. In the above case, serial
execution will return wrong results. Maybe we should throw an error or probably
just log a warning? After all it is just a hint and it is up to the query
engine to decide whether or not to honor it?
[~ankit.singhal] - Good catch on the table name in the log line in
SerialIterators.java. I have fixed it. I moved the helper methods in
QueryWithOffsetIT towards the end of the file as it made it convenient to
comment tests out.
> Query with large number of guideposts is slower compared to no stats
> --------------------------------------------------------------------
>
> Key: PHOENIX-2724
> URL: https://issues.apache.org/jira/browse/PHOENIX-2724
> Project: Phoenix
> Issue Type: Bug
> Affects Versions: 4.7.0
> Environment: Phoenix 4.7.0-RC4, HBase-0.98.17 on a 8 node cluster
> Reporter: Mujtaba Chohan
> Assignee: Samarth Jain
> Fix For: 4.8.0
>
> Attachments: PHOENIX-2724.patch, PHOENIX-2724_v2.patch
>
>
> With 1MB guidepost width for ~900GB/500M rows table. Queries with short scan
> range gets significantly slower.
> Without stats:
> {code}
> select * from T limit 10; // query execution time <100 msec
> {code}
> With stats:
> {code}
> select * from T limit 10; // query execution time >20 seconds
> Explain plan: CLIENT 876085-CHUNK 476569382 ROWS 876060986727 BYTES SERIAL
> 1-WAY FULL SCAN OVER T SERVER 10 ROW LIMIT CLIENT 10 ROW LIMIT
> {code}
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