Glauber Costa e0bfd1c40a allow Cassandra SSTables with counters to be imported if they are new enough ...

Right now Cassandra SSTables with counters cannot be imported into
Scylla.  The reason for that is that Cassandra changed their counter
representation in their 2.1 version and kept transparently supporting
both representations.  We do not support their old representation, nor
there is a sane way to figure out by looking at the data which one is in
use.

For safety, we had made the decision long ago to not import any
tables with counters: if a counter was generated in older Cassandra, we
would misrepresent them.

In this patch, I propose we offer a non-default way to import SSTables
with counters: we can gate it with a flag, and trust that the user knows
what they are doing when flipping it (at their own peril). Cassandra 2.1
is by now pretty old. many users can safely say they've never used
anything older.

While there are tools like sstableloader that can be used to import
those counters, there are often situations in which directly importing
SSTables is either better, faster, or worse: the only option left.  I
argue that having a flag that allow us to import them when we are sure
it is safe is better than having no option at all.

With this patch I was able to successfully import Cassandra tables with
counters that were generated in Cassandra 2.1, reshard and compact their
SSTables, and read the data back to get the same values in Scylla as in
Cassandra.

Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <20190210154028.12472-1-glauber@scylladb.com>

2019-02-10 17:50:48 +02:00

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