When partition has no live regular rows, but has some data live in the
static row, then it should appear in the results, even though we
didn't select any static column.
To reproduce:
create table cf (k blob, c blob, v blob, s1 blob static, primary key (k, c));
update cf set s1 = 0x01 where k = 0x01;
update cf set s1 = 0x02 where k = 0x02;
select k from cf;
The "select" statement should return 2 rows, but was returning 0.
The following query worked fine, because static columns were included:
select * from cf;
The data query should contain only live data, so we shouldn't write a
partition entry if it's supposed to be absent from the results. We
can'r tell that though until we've processed all the data. To solve
this problem, query result writer is using an optimistic approach,
where the partition header will be retracted from the buffer
(cheaply), if it turns out there's no live data in it.
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