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The sstable parsing code calls mp_row_consumer::flush() after every
clustering row has been read, and this puts the now complete row in a single
field "_ready". The assumption is that at this point parsing will stop, the
consumer will move out this _ready (mp_row_consumer::get_mutation_fragment())
and when flush() is later called again, _ready will be empty again.
This assumption is correct in our code, but is based on an intricate
combination of estoreric parts of the code, such as:
1. In data_consume_row_context we stop parsing after reading the parition's
header, before reading any clustering rows, giving the caller the chance
to call sstable_streamed_mutation::read_next() to be prepared for the
incoming mutations.
2. In mp_row_consumer::flush_if_needed(), we stop the parser after each
individual clustering row.
It is easy to break this assumption, and I did this in one of my code changes,
and the result was silent loss of clustering rows, as "_ready" got silently
overwritten before the reader had a chance to move it out.
What this patch does is to add an assertion: If a clustering row is silently
lost before being transferred to the mutation fragment reader, we croak.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <1468389955-24600-1-git-send-email-nyh@scylladb.com>