"This patchset implements load_new_sstables, allowing one to move tables inside the
data directory of a CF, and then call "nodetool refresh" to start using them.
Keep in mind that for Cassandra, this is deemed an unsafe operation:
https://issues.apache.org/jira/browse/CASSANDRA-6245
It is still for us something we should not recommend - unless the CF is totally
empty and not yet used, but we can do a much better job in the safety front.
To guarantee that, the process works in four steps:
1) All writes to this specific column family are disabled. This is a horrible thing to
do, because dirty memory can grow much more than desired during this. Throughout out
this implementation, we will try to keep the time during which the writes are disabled
to its bare minimum.
While disabling the writes, each shard will tell us about the highest generation number
it has seen.
2) We will scan all tables that we haven't seen before. Those are any tables found in the
CF datadir, that are higher than the highest generation number seen so far. We will link
them to new generation numbers that are sequential to the ones we have so far, and end up
with a new generation number that is returned to the next step
3) The generation number computed in the previous step is now propagated to all CFs, which
guarantees that all further writes will pick generation numbers that won't conflict with
the existing tables. Right after doing that, the writes are resumed.
4) The tables we found in step 2 are passed on to each of the CFs. They can now load those
tables while operations to the CF proceed normally."
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