Add tool for cross-cluster split-metric migrations

[replay]

fixes #528

This tool can be used like shown here:

mst@ubuntu:~/go/src/github.com/raintank/metrictank/cmd/mt-split-metrics-by-ttl$ ./cross_cluster_tool.py --destination-address 192.168.56.101 --temp-dir /tmp/met/ 840 8640 
nodetool snapshot -t migration-1 --table metrics metrictank &&
mkdir -p /tmp/met &&
ln -s /var/lib/cassandra/data/metrictank/metrics/snapshots/migration-1 /tmp/met/metrictank/metrics_512 &&
ln -s /var/lib/cassandra/data/metrictank/metrics/snapshots/migration-1 /tmp/met/metrictank/metrics_8192 &&
sstableloader -d 192.168.56.101 /tmp/met/metrictank/metrics_512 &&
sstableloader -d 192.168.56.101 /tmp/met/metrictank/metrics_8192
mst@ubuntu:~/go/src/github.com/raintank/metrictank/cmd/mt-split-metrics-by-ttl$ ./cross_cluster_tool.py --destination-address 192.168.56.101 --temp-dir /tmp/met/ 840 8640 > migrate.sh
mst@ubuntu:~/go/src/github.com/raintank/metrictank/cmd/mt-split-metrics-by-ttl$ . migrate.sh

[woodsaj]

cassandra stores tables in directories with a unique hash suffixed to the table name.
So you will need to look in '{data_dir}/{src_kspace}/' for a director that starts with "{src_table}-"

eg, the directory is something like

/var/lib/cassandra/data/raintank/metric-5f3434601d1e11e6886b212ea10d84c9/

[replay]

right, i missed that. This should fix it: ab6d214

[Dieterbe]

what's the status of this? needs reviewing? can be merged? should it even still be merged (as in, is it still a relevant use case)

[replay]

I think we've actually used that for one of the migrations but then forgot to merge the PR. @woodsaj is that ok to merge?

[replay]

Considering that this only adds a file and hence can't break anything I'm thinking i should just merge it

[woodsaj]

LGTM