Jack Krupansky <jack.krupansky <at> gmail.com> writes: > > > If your data is replicated properly (RF=3) and you do QUORUM reads and writes, you should be able to shut down one node, adjust the configuration, and restart that node and all should be fine. Do it quickly enough (less than an hour) and the node should quickly catch up with any changes. > How small is small? Six nodes? > > > -- Jack Krupansky > On Mon, Mar 7, 2016 at 5:57 AM, Krzysztof Księżyk <kksiezyk <at> gmail.com> wrote:Hi, > I have small Cassandra cluster running on boxes with 256GB SSD and 2TB HDD. > Originally SSD was for system and commit log and HDD for data. But > unfortunately because of nature of queries, performance was not satisfactory > and to improve it, data were moved to SSD as well. Now problem is with SSD > size being too small to keep all data. As there's one keyspace created a > month, my idea was to move historical keyspaces to HDD and make a symlink. > These historical keyspaces are not queried often so it shouldn't affect > performance much. I've written simple script that rsyncs data, stops > Cassandra, makes symlink and starts Cassandra node again, but I have question > if there will be problem if I make hotswap - without stopping Cassandra > daemon. So... rsync, rename current keyspace folder in data dir, make symlink > to new location on HDD. One good thing is that while keyspace is fully feed > with data, it no longer changes. I see on lsof output that even if keyspace > is not queried, Cassandra keeps files opened, so I guess it's not safe to > hotswap, but I'd like to make sure. > Kind regards - > Krzysztof Ksiezyk > > > > >
Hi, Thank you for answer. Small cluster - 4 boxes. Data has RF=2 and worker uses read-consistency-level = ONE. Good thing is that data is immutable in keyspace after initial load, but problem is that worker querying Cassandra (using Titan) dies when node it uses, is down, even for a short period. Seems it's by bad design of worker but I can't fix it easily now, so initial idea was to preserve Cassandra online whole the time. Kind regards - Krzysztof Ksiezyk
