1. 27 Jun, 2017 1 commit
    • antirez's avatar
      RDB modules values serialization format version 2. · 365dd037
      antirez authored
      The original RDB serialization format was not parsable without the
      module loaded, becuase the structure was managed only by the module
      itself. Moreover RDB is a streaming protocol in the sense that it is
      both produce di an append-only fashion, and is also sometimes directly
      sent to the socket (in the case of diskless replication).
      
      The fact that modules values cannot be parsed without the relevant
      module loaded is a problem in many ways: RDB checking tools must have
      loaded modules even for doing things not involving the value at all,
      like splitting an RDB into N RDBs by key or alike, or just checking the
      RDB for sanity.
      
      In theory module values could be just a blob of data with a prefixed
      length in order for us to be able to skip it. However prefixing the values
      with a length would mean one of the following:
      
      1. To be able to write some data at a previous offset. This breaks
      stremaing.
      2. To bufferize values before outputting them. This breaks performances.
      3. To have some chunked RDB output format. This breaks simplicity.
      
      Moreover, the above solution, still makes module values a totally opaque
      matter, with the fowllowing problems:
      
      1. The RDB check tool can just skip the value without being able to at
      least check the general structure. For datasets composed mostly of
      modules values this means to just check the outer level of the RDB not
      actually doing any checko on most of the data itself.
      2. It is not possible to do any recovering or processing of data for which a
      module no longer exists in the future, or is unknown.
      
      So this commit implements a different solution. The modules RDB
      serialization API is composed if well defined calls to store integers,
      floats, doubles or strings. After this commit, the parts generated by
      the module API have a one-byte prefix for each of the above emitted
      parts, and there is a final EOF byte as well. So even if we don't know
      exactly how to interpret a module value, we can always parse it at an
      high level, check the overall structure, understand the types used to
      store the information, and easily skip the whole value.
      
      The change is backward compatible: older RDB files can be still loaded
      since the new encoding has a new RDB type: MODULE_2 (of value 7).
      The commit also implements the ability to check RDB files for sanity
      taking advantage of the new feature.
      365dd037
  2. 19 May, 2017 1 commit
  3. 18 Apr, 2017 1 commit
  4. 17 Apr, 2017 1 commit
  5. 13 Dec, 2016 1 commit
    • 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. 01 Dec, 2016 1 commit
  7. 10 Nov, 2016 1 commit
    • antirez's avatar
      PSYNC2: Save replication ID/offset on RDB file. · 28c96d73
      antirez authored
      This means that stopping a slave and restarting it will still make it
      able to PSYNC with the master. Moreover the master itself will retain
      its ID/offset, in case it gets turned into a slave, or if a slave will
      try to PSYNC with it with an exactly updated offset (otherwise there is
      no backlog).
      
      This change was possible thanks to PSYNC v2 that makes saving the current
      replication state much simpler.
      28c96d73
  8. 09 Nov, 2016 1 commit
    • antirez's avatar
      PSYNC2: different improvements to Redis replication. · 2669fb83
      antirez authored
      The gist of the changes is that now, partial resynchronizations between
      slaves and masters (without the need of a full resync with RDB transfer
      and so forth), work in a number of cases when it was impossible
      in the past. For instance:
      
      1. When a slave is promoted to mastrer, the slaves of the old master can
      partially resynchronize with the new master.
      
      2. Chained slalves (slaves of slaves) can be moved to replicate to other
      slaves or the master itsef, without requiring a full resync.
      
      3. The master itself, after being turned into a slave, is able to
      partially resynchronize with the new master, when it joins replication
      again.
      
      In order to obtain this, the following main changes were operated:
      
      * Slaves also take a replication backlog, not just masters.
      
      * Same stream replication for all the slaves and sub slaves. The
      replication stream is identical from the top level master to its slaves
      and is also the same from the slaves to their sub-slaves and so forth.
      This means that if a slave is later promoted to master, it has the
      same replication backlong, and can partially resynchronize with its
      slaves (that were previously slaves of the old master).
      
      * A given replication history is no longer identified by the `runid` of
      a Redis node. There is instead a `replication ID` which changes every
      time the instance has a new history no longer coherent with the past
      one. So, for example, slaves publish the same replication history of
      their master, however when they are turned into masters, they publish
      a new replication ID, but still remember the old ID, so that they are
      able to partially resynchronize with slaves of the old master (up to a
      given offset).
      
      * The replication protocol was slightly modified so that a new extended
      +CONTINUE reply from the master is able to inform the slave of a
      replication ID change.
      
      * REPLCONF CAPA is used in order to notify masters that a slave is able
      to understand the new +CONTINUE reply.
      
      * The RDB file was extended with an auxiliary field that is able to
      select a given DB after loading in the slave, so that the slave can
      continue receiving the replication stream from the point it was
      disconnected without requiring the master to insert "SELECT" statements.
      This is useful in order to guarantee the "same stream" property, because
      the slave must be able to accumulate an identical backlog.
      
      * Slave pings to sub-slaves are now sent in a special form, when the
      top-level master is disconnected, in order to don't interfer with the
      replication stream. We just use out of band "\n" bytes as in other parts
      of the Redis protocol.
      
      An old design document is available here:
      
      https://gist.github.com/antirez/ae068f95c0d084891305
      
      However the implementation is not identical to the description because
      during the work to implement it, different changes were needed in order
      to make things working well.
      2669fb83
  9. 06 Oct, 2016 1 commit
    • antirez's avatar
      Module: Ability to get context from IO context. · 152c1b68
      antirez authored
      It was noted by @dvirsky that it is not possible to use string functions
      when writing the AOF file. This sometimes is critical since the command
      rewriting may need to be built in the context of the AOF callback, and
      without access to the context, and the limited types that the AOF
      production functions will accept, this can be an issue.
      
      Moreover there are other needs that we can't anticipate regarding the
      ability to use Redis Modules APIs using the context in order to build
      representations to emit AOF / RDB.
      
      Because of this a new API was added that allows the user to get a
      temporary context from the IO context. The context is auto released
      if obtained when the RDB / AOF callback returns.
      
      Calling multiple time the function to get the context, always returns
      the same one, since it is invalid to have more than a single context.
      152c1b68
  10. 02 Oct, 2016 1 commit
  11. 19 Sep, 2016 2 commits
  12. 01 Sep, 2016 1 commit
    • antirez's avatar
      Fix rdb.c var types when calling rdbLoadLen(). · 57a0db94
      antirez authored
      Technically as soon as Redis 64 bit gets proper support for loading
      collections and/or DBs with more than 2^32 elements, the 32 bit version
      should be modified in order to check if what we read from rdbLoadLen()
      overflows. This would only apply to huge RDB files created with a 64 bit
      instance and later loaded into a 32 bit instance.
      57a0db94
  13. 11 Aug, 2016 1 commit
  14. 09 Aug, 2016 2 commits
  15. 21 Jul, 2016 1 commit
    • antirez's avatar
      Avoid simultaneous RDB and AOF child process. · 0a628e51
      antirez authored
      This patch, written in collaboration with Oran Agra (@oranagra) is a companion
      to 780a8b1d. Together the two patches should avoid that the AOF and RDB saving
      processes can be spawned at the same time. Previously conditions that
      could lead to two saving processes at the same time were:
      
      1. When AOF is enabled via CONFIG SET and an RDB saving process is
         already active.
      
      2. When the SYNC command decides to start an RDB saving process ASAP in
         order to serve a new slave that cannot partially resynchronize (but
         only if we have a disk target for replication, for diskless
         replication there is not such a problem).
      
      Condition "1" is not very severe but "2" can happen often and is
      definitely good at degrading Redis performances in an unexpected way.
      
      The two commits have the effect of always spawning RDB savings for
      replication in replicationCron() instead of attempting to start an RDB
      save synchronously. Moreover when a BGSAVE or AOF rewrite must be
      performed, they are instead just postponed using flags that will try to
      perform such operations ASAP.
      
      Finally the BGSAVE command was modified in order to accept a SCHEDULE
      option so that if an AOF rewrite is in progress, when this option is
      given, the command no longer returns an error, but instead schedules an
      RDB rewrite operation for when it will be possible to start it.
      0a628e51
  16. 01 Jul, 2016 3 commits
  17. 05 Jun, 2016 1 commit
  18. 03 Jun, 2016 1 commit
  19. 01 Jun, 2016 3 commits
  20. 25 Apr, 2016 2 commits
  21. 15 Feb, 2016 1 commit
  22. 01 Oct, 2015 3 commits
  23. 07 Sep, 2015 1 commit
    • antirez's avatar
      Undo slaves state change on failed rdbSaveToSlavesSockets(). · 8e555374
      antirez authored
      As Oran Agra suggested, in startBgsaveForReplication() when the BGSAVE
      attempt returns an error, we scan the list of slaves in order to remove
      them since there is no way to serve them currently.
      
      However we check for the replication state BGSAVE_START, which was
      modified by rdbSaveToSlaveSockets() before forking(). So when fork fails
      the state of slaves remain BGSAVE_END and no cleanup is performed.
      
      This commit fixes the problem by making rdbSaveToSlavesSockets() able to
      undo the state change on fork failure.
      8e555374
  24. 05 Aug, 2015 2 commits
    • antirez's avatar
    • antirez's avatar
      Make sure we re-emit SELECT after each new slave full sync setup. · 15de6b10
      antirez authored
      In previous commits we moved the FULLRESYNC to the moment we start the
      BGSAVE, so that the offset we provide is the right one. However this
      also means that we need to re-emit the SELECT statement every time a new
      slave starts to accumulate the changes.
      
      To obtian this effect in a more clean way, the function that sends the
      FULLRESYNC reply was overloaded with a more important role of also doing
      this and chanigng the slave state. So it was renamed to
      replicationSetupSlaveForFullResync() to better reflect what it does now.
      15de6b10
  25. 04 Aug, 2015 1 commit
    • antirez's avatar
      PSYNC initial offset fix. · 292fec05
      antirez authored
      This commit attempts to fix a bug involving PSYNC and diskless
      replication (currently experimental) found by Yuval Inbar from Redis Labs
      and that was later found to have even more far reaching effects (the bug also
      exists when diskstore is off).
      
      The gist of the bug is that, a Redis master replies with +FULLRESYNC to
      a PSYNC attempt that fails and requires a full resynchronization.
      However, the baseline offset sent along with FULLRESYNC was always the
      current master replication offset. This is not ok, because there are
      many reasosn that may delay the RDB file creation. And... guess what,
      the master offset we communicate must be the one of the time the RDB
      was created. So for example:
      
      1) When the BGSAVE for replication is delayed since there is one
         already but is not good for replication.
      2) When the BGSAVE is not needed as we attach one currently ongoing.
      3) When because of diskless replication the BGSAVE is delayed.
      
      In all the above cases the PSYNC reply is wrong and the slave may
      reconnect later claiming to need a wrong offset: this may cause
      data curruption later.
      292fec05
  26. 27 Jul, 2015 1 commit
  27. 26 Jul, 2015 4 commits