Thanks for the information Alexander and Daniel, I appreciated it. We are using Riak2.0 and bitcask as backend, and we are writing the keys once into bucket, keep it for a few hours, then delete it, never update the existing data.
On Wed, Apr 20, 2016 at 11:32 AM, Alexander Sicular <sicul...@gmail.com> wrote: > Hello Shifeng, > > Riak uses Bitcask as its default data backend, it may also use leveldb > as a backend but must be configured to do so[0][1]. Both bitcask[2] > and leveldb[3] do not reclaim disk space immediately when a delete is > issued. Incidentally, neither do updates. Because Riak is > non-destructive, aka append only, aka no in-place updates, mutation > operations like updates or deletes are actually writes. For example, a > 10KB object that is updated four times in some short interval will > consume 50KB space (original 10KB + 4 x 10KB updates) until > merge/compaction occurs. A delete is actually a special zero byte > value write indicating a key is marked for deletion, aka a tombstone. > Bitcask will reclaim disk space via merge operations which may be > controlled by the user. Leveldb reclaims disk space via compaction > operations. > > Architects and Developers should take into account their update/delete > ratios and consider how those will affect disk space consumption and > consider how deletes operate in distributed systems in general and > Riak in specific from an application perspective. John Daily wrote a > must read four part series on Riak's configurable behaviors that all > Riak developers should be familiar with. Part 3 deals specifically > with delete related considerations[4]. > > Thank you, > Alexander > > [0] > http://docs.basho.com/riak/kv/latest/setup/planning/backend/leveldb/#installing-eleveldb > [1] http://docs.basho.com/riak/kv/latest/configuring/backend/ > [2] http://docs.basho.com/riak/kv/latest/setup/planning/backend/bitcask/ > [3] http://docs.basho.com/riak/kv/latest/setup/planning/backend/leveldb/ > [4] http://basho.com/posts/technical/riaks-config-behaviors-part-3/ > > On Wed, Apr 20, 2016 at 8:17 AM, Daniel Abrahamsson > <daniel.abrahams...@klarna.com> wrote: > > Hi, > > > > What riak version and what riak backend are you using? For leveldb you > have > > to take compaction into account, and for older bitcask versions there are > > known issues with data not being properly deleted. > > > > //Daniel > > > > _______________________________________________ > > riak-users mailing list > > riak-users@lists.basho.com > > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com > > >
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