1. 23 Jun, 2017 1 commit
    • antirez's avatar
      Issue #4027: unify comment and modify return value in freeMemoryIfNeeded(). · c9097393
      antirez authored
      It looks safer to return C_OK from freeMemoryIfNeeded() when clients are
      paused because returning C_ERR may prevent success of writes. It is
      possible that there is no difference in practice since clients cannot
      execute writes while clients are paused, but it looks more correct this
      way, at least conceptually.
      
      Related to PR #4028.
      c9097393
  2. 13 Jun, 2017 1 commit
  3. 01 Jun, 2017 1 commit
  4. 08 Apr, 2017 1 commit
  5. 13 Dec, 2016 4 commits
    • antirez's avatar
      Writable slaves expires: fix leak in key tracking. · b6f871cf
      antirez authored
      We need to use a dictionary type that frees the key, since we copy the
      keys in the dictionary we use to track expires created in the slave
      side.
      b6f871cf
    • antirez's avatar
      INFO: show num of slave-expires keys tracked. · d1adc85a
      antirez authored
      d1adc85a
    • antirez's avatar
      Fix created->created typo in expire.c · 5b9ba264
      antirez authored
      5b9ba264
    • antirez's avatar
      Replication: fix the infamous key leakage of writable slaves + EXPIRE. · 04542cff
      antirez authored
      BACKGROUND AND USE CASEj
      
      Redis slaves are normally write only, however the supprot a "writable"
      mode which is very handy when scaling reads on slaves, that actually
      need write operations in order to access data. For instance imagine
      having slaves replicating certain Sets keys from the master. When
      accessing the data on the slave, we want to peform intersections between
      such Sets values. However we don't want to intersect each time: to cache
      the intersection for some time often is a good idea.
      
      To do so, it is possible to setup a slave as a writable slave, and
      perform the intersection on the slave side, perhaps setting a TTL on the
      resulting key so that it will expire after some time.
      
      THE BUG
      
      Problem: in order to have a consistent replication, expiring of keys in
      Redis replication is up to the master, that synthesize DEL operations to
      send in the replication stream. However slaves logically expire keys
      by hiding them from read attempts from clients so that if the master did
      not promptly sent a DEL, the client still see logically expired keys
      as non existing.
      
      Because slaves don't actively expire keys by actually evicting them but
      just masking from the POV of read operations, if a key is created in a
      writable slave, and an expire is set, the key will be leaked forever:
      
      1. No DEL will be received from the master, which does not know about
      such a key at all.
      
      2. No eviction will be performed by the slave, since it needs to disable
      eviction because it's up to masters, otherwise consistency of data is
      lost.
      
      THE FIX
      
      In order to fix the problem, the slave should be able to tag keys that
      were created in the slave side and have an expire set in some way.
      
      My solution involved using an unique additional dictionary created by
      the writable slave only if needed. The dictionary is obviously keyed by
      the key name that we need to track: all the keys that are set with an
      expire directly by a client writing to the slave are tracked.
      
      The value in the dictionary is a bitmap of all the DBs where such a key
      name need to be tracked, so that we can use a single dictionary to track
      keys in all the DBs used by the slave (actually this limits the solution
      to the first 64 DBs, but the default with Redis is to use 16 DBs).
      
      This solution allows to pay both a small complexity and CPU penalty,
      which is zero when the feature is not used, actually. The slave-side
      eviction is encapsulated in code which is not coupled with the rest of
      the Redis core, if not for the hook to track the keys.
      
      TODO
      
      I'm doing the first smoke tests to see if the feature works as expected:
      so far so good. Unit tests should be added before merging into the
      4.0 branch.
      04542cff
  6. 06 Jul, 2016 1 commit