Botond Dénes 9661769313 combined_mutation_reader: fix fast-fowarding related row-skipping bug ...

When fast forwarding is enabled and all readers positioned inside the
current partition return EOS, return EOS from the combined-reader
too. Instead of skipping to the next partition if there are idle readers
(positioned at some later partition) available. This will cause rows to
be skipped in some cases.

The fix is to distinguish EOS'd readers that are only halted (waiting
for a fast-forward) from thoose really out of data. To achieve this we
track the last fragment-kind the reader emitted. If that was a
partition-end then the reader is out of data, otherwise it might emit
more fragments after a fast-forward. Without this additional information
it is impossible to determine why a reader reached EOS and the code
later may make the wrong decision about whether the combined-reader as
a whole is at EOS or not.
Also when fast-forwarding between partition-ranges or calling
next_partition() we set the last fragment-kind of forwarded readers
because they should emit a partition-start, otherwise they are out of
data.

Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <6f0b21b1ec62e1197de6b46510d5508cdb4a6977.1512569218.git.bdenes@scylladb.com>

2017-12-06 16:09:05 +02:00

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