get_count paging often asks for a page uselessly
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Key: CASSANDRA-3798
URL: https://issues.apache.org/jira/browse/CASSANDRA-3798
Project: Cassandra
Issue Type: Improvement
Affects Versions: 1.0.0
Reporter: Sylvain Lebresne
Assignee: Sylvain Lebresne
Priority: Minor
Fix For: 1.1
Current get_count paging stopping condition is:
{noformat}
if ((requestedCount == 0) || ((columns.size() == 1) &&
(lastName.equals(predicate.slice_range.start))))
{
break;
}
{noformat}
On a "count how many columns this row has" query (arguably the main reason why
you'd use get_count), requestedCount will never be 0, and so we'll stop
whenever a page has only returned the last column of the preceding page. While
this isn't wrong, we could stop as soon as a page returns less element than
requested and avoid querying that last 1 column page.
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