[
https://issues.apache.org/jira/browse/CASSANDRA-12417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15548442#comment-15548442
]
Alex Petrov commented on CASSANDRA-12417:
-----------------------------------------
I've split the 3.0 in two commits. {{avg}} improvements go to {{3.0}} and up,
{{sum}} go to {{3.X}} and up and re-triggered CI:
|[3.0-split|https://github.com/ifesdjeen/cassandra/tree/12417-3.0-split]|[utest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-3.0-split-testall/]|[dtest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-3.0-split-dtest/]|
|[3.X-split|https://github.com/ifesdjeen/cassandra/tree/12417-3.X-split]|[utest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-3.X-split-testall/]|[dtest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-3.X-split-dtest/]|
|[trunk-split|https://github.com/ifesdjeen/cassandra/tree/12417-trunk-split]|[utest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-trunk-split-testall/]|[dtest|https://cassci.datastax.com/view/Dev/view/ifesdjeen/job/ifesdjeen-12417-trunk-split-dtest/]|
> Built-in AVG aggregate is much less useful than it should be
> ------------------------------------------------------------
>
> Key: CASSANDRA-12417
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12417
> Project: Cassandra
> Issue Type: Bug
> Components: CQL
> Reporter: Branimir Lambov
> Assignee: Alex Petrov
>
> For fixed-size integer types overflow is all but guaranteed to happen,
> yielding incorrect result. While for sum it is somewhat acceptable as the
> result cannot fit the type, this is not the case for average.
> As the result of average is always within the scope of the source type,
> failing to produce it only signifies a bad implementation. Yes, one can solve
> this by type-casting, but do we really want to always have to be telling
> people that the correct spelling of the average function is
> {{cast(avg(cast(value as bigint))) as int)}}, especially if this is so
> trivial to fix?
> Additionally, the straightforward addition we use for floating point versions
> is not a good choice numerically for larger numbers of values. We should
> switch to a more stable version, e.g. iterative mean using {{avg = avg +
> (value - avg) / count}}.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
