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Redis 2.6 release notes

** IMPORTANT ** Check the 'Migrating from 2.4 to 2.6' section at the end of
                this file for information about what changed between 2.4 and
                2.6 and how this may affect your application.

Upgrade urgency levels:

LOW:      No need to upgrade unless there are new features you want to use.
MODERATE: Program an upgrade of the server, but it's not urgent.
HIGH:     There is a critical bug that may affect some part of users. Upgrade!
CRITICAL: There is a critical bug affecting MOST USERS. Upgrade ASAP.

---[ Redis 2.5.10 (2.6 Release Candidate 4) ]


* [BUGFIX]   Allow PREFIX to be overwritten on "make install".
* [BUGFIX]   Run the test with just one client if the computer is slow.
* [BUGFIX]   Event port support in our event driven libray.
* [BUGFIX]   Jemalloc updated to 3.0.0. This fixes a possibly AOF rewrite issue.
             See https://github.com/antirez/redis/issues/504 for info.
* [BUGFIX]   Fixed issue #516: ZINTERSTORE / ZUNIONSTORE with mixed sets/zsets.
* [BUGFIX]   Set fd to writable when poll(2) detects POLLERR or POLLHUP event.
* [BUGFIX]   Fixed RESTORE hash failure (Issue #532).
* [IMPROVED] Allow an AOF rewrite buffer > 2GB (Related to issue #504).
* [IMPROVED] Server cron function frequency is now configurable (REDIS_HZ).
* [IMPROVED] Better, less blocking expired keys collection algorithm.
* [FEATURE]  New commands: BITOP and BITCOUNT.
* [FEATURE]  redis-cli --pipe for mass import.

What's new in Redis 2.5.9 (aka 2.6 Release Candidate 3)

UPGRADE URGENCY: critical, upgrade ASAP.

* [BUGFIX] Fix for issue #500 (https://github.com/antirez/redis/pull/500).
           Redis 2.6-RC1 and RC2 may corrupt ziplist-encoded sorted sets
           produced by Redis 2.4.x.
* [BUGFIX] Fixed several bugs in init.d script.
* [BUGFIX] syncio.c functions modified for speed and correctness. On osx
           (and possibly other BSD-based systems) the slave would block on
           replication to send the SYNC command when the master was not
           available. This is fixed now, but was not affecting Linux installs.
* Now when slave-serve-stale-data is set to yes and the master is down, instead
  of reporting a generic error Redis replies with -MASTERDOWN.

What's new in Redis 2.5.8 (aka 2.6 Release Candidate 2)

UPGRADE URGENCY: high for all the users of the KEYS command, otherwise low.

* [BUGFIX] Fix for KEYS command: if the DB contains keys with expires the KEYS
           command may return the wrong output, having duplicated or missing
           keys. See issue #487 and #488 on github for details.

What's new in Redis 2.5.7 (aka 2.6 Release Candidate 1)

UPGRADE URGENCY: upgrade not recommended because this is an RC release.

* This is the first release candidate for Redis 2.6. We are not aware of
  bugs, but part of this code is young and was never tested in production
  environments, so handle with care.

An overview of new features and changes in Redis 2.6.x

* Server side Lua scripting, see http://redis.io/commands/eval
* Virtual Memory removed (was deprecated in 2.4)
* Hardcoded limits about max number of clients removed.
* AOF low level semantics is generally more sane, and especially when used
  in slaves.
* Milliseconds resolution expires, also added new commands with milliseconds
  precision (PEXPIRE, PTTL, ...).
* Better memory usage for "small" lists, ziplists and hashes when fields or
  values contain small integers.
* Read only slaves.
* New bit opeations: BITCOUNT and BITOP commands.
* Clients max output buffer soft and hard limits. You can specifiy different
  limits for different classes of clients (normal,pubsub,slave).
* More incremental (less blocking) expired keys collection algorithm, in
  practical terms this means that Redis is more responsive when a very
  big number of keys expire about at the same time.
* AOF is now able to rewrite aggregate data types using variadic commands,
  often producing an AOF that is faster to save, load, and is smaller in size.
* Every redis.conf directive is now accepted as a command line option for the
  redis-server binary, with the same name and number of arguments.
* Hash table seed randomization for protection against collisions attacks.
* Performances improved when writing large objects to Redis.
* Integrated memory test, see redis-server --test-memory.
* New DUMP, RESTORE, MIGRATE commands (back ported from Redis Cluster to 2.6).
* CRC64 checksump in RDB files.
* Better MONITOR output and behavior (now commands are logged before execution).
* "Software Watchdog" feature to debug latency issues.
* Significant parts of the core refactored or rewritten. New internal APIs
  and core changes allowed to develop Redis Cluster on top of the new code,
  however for 2.6 all the cluster code was removed, and will be released with
  Redis 3.0 when it is more complete and stable.
* Redis ASCII art logo added at startup.
* Crash report on memory violation or failed asserts improved significantly
  to make debugging of hard to catch bugs simpler.
* redis-benchmark improvements: ability to run selected tests,
  CSV output, faster, better help.
* redis-cli improvements: --eval for comfortable development of Lua scripts.
* SHUTDOWN now supports two optional arguments: "SAVE" and "NOSAVE".
* INFO output split into sections, the command is now able to just show 
  pecific sections.
* New statistics about how many time a command was called, and how much
  execution time it used (INFO commandstats).
* More predictable SORT behavior in edge cases.
* Better support for big endian and *BSD systems.
* Build system improved.

Migrating from 2.4 to 2.6

Redis 2.4 is mostly a strict subset of 2.6. However there are a few things
that you should be aware of:

* You can't use .rdb and AOF files generated with 2.6 into a 2.4 instance.
* 2.4 slaves can be attached to 2.6 masters, but not the contrary, and only
  for the time needed to perform the version upgrade.

There are also a few API differences, that are unlikely to cause problems,
but it is better to keep them in mind:

* SORT now will refuse to sort in numerical mode elements that can't be parsed
  as numbers.
* EXPIREs now all have millisecond resolution (but this is very unlikely to
  break code that was not conceived exploting the previous resolution error
  in some way.)
* INFO output is a bit different now, and contains empty lines and comments
  starting with '#'. All the major clients should be already fixed to work
  with the new INFO format.
* Slaves are only read-only by default (but you can change this easily
  setting the "slave-read-only" configuration option to "no" editing your
  redis.conf or using CONFIG SET.

The following INFO fields were renamed for consistency:

     changes_since_last_save -> rdb_changes_since_last_save
     bgsave_in_progress -> rdb_bgsave_in_progress
     last_save_time -> rdb_last_save_time
     last_bgsave_status -> rdb_last_bgsave_status
     bgrewriteaof_in_progress -> aof_rewrite_in_progress
     bgrewriteaof_scheduled -> aof_rewrite_scheduled

The following redis.conf and CONFIG GET / SET parameters changed:

    * hash-max-zipmap-entries, now replaced by hash-max-ziplist-entries
    * hash-max-zipmap-value, now replaced by hash-max-ziplist-value
    * glueoutputbuf option was now completely removed (was deprecated)


Credits: Where not specified the implementation and design are done by
Salvatore Sanfilippo and Pieter Noordhuis. Thanks to VMware for making all
this possible. Also many thanks to all the other contributors and the amazing
community we have.

See commit messages for more credits.