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Defrag: document the feature in redis.conf.

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antirez 2017-01-11 17:24:49 +01:00
parent 6ad34a4b78
commit 634b096610
1 changed files with 49 additions and 6 deletions
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redis.conf
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@ -1230,21 +1230,64 @@ aof-rewrite-incremental-fsync yes
# lfu-decay-time 1
########################### ACTIVE DEFRAGMENTATION #######################
#
# WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested
# even in production and manually tested by multiple engineers for some
# time.
#
# What is active defragmentation?
# -------------------------------
#
# Active (online) defragmentation allows a Redis server to compact the
# spaces left between small allocations and deallocations of data in memory,
# thus allowing to reclaim back memory.
#
# Fragmentation is a natural process that happens with every allocator (but
# less so with Jemalloc, fortunately) and certain workloads. Normally a server
# restart is needed in order to lower the fragmentation, or at least to flush
# away all the data and create it again. However thanks to this feature
# implemented by Oran Agra for Redis 4.0 this process can happen at runtime
# in an "hot" way, while the server is running.
#
# Basically when the fragmentation is over a certain level (see the
# configuration options below) Redis will start to create new copies of the
# values in contiguous memory regions by exploiting certain specific Jemalloc
# features (in order to understand if an allocation is causing fragmentation
# and to allocate it in a better place), and at the same time, will release the
# old copies of the data. This process, repeated incrementally for all the keys
# will cause the fragmentation to drop back to normal values.
#
# Important things to understand:
#
# 1. This feature is disabled by default, and only works if you compiled Redis
# to use the copy of Jemalloc we ship with the source code of Redis.
# This is the default with Linux builds.
#
# 2. You never need to enable this feature if you don't have fragmentation
# issues.
#
# 3. Once you experience fragmentation, you can enable this feature when
# needed with the command "CONFIG SET activedefrag yes".
#
# The configuration parameters are able to fine tune the behavior of the
# defragmentation process. If you are not sure about what they mean it is
# a good idea to leave the defaults untouched.
# enabled active defragmentation
# Enabled active defragmentation
# activedefrag yes
# minimum amount of fragmentation waste to start active defrag
# Minimum amount of fragmentation waste to start active defrag
# active-defrag-ignore-bytes 100mb
# minimum percentage of fragmentation to start active defrag
# Minimum percentage of fragmentation to start active defrag
# active-defrag-threshold-lower 10
# maximum percentage of fragmentation at which we use maximum effort
# Maximum percentage of fragmentation at which we use maximum effort
# active-defrag-threshold-upper 100
# minimal effort for defrag in CPU percentage
# Minimal effort for defrag in CPU percentage
# active-defrag-cycle-min 25
# maximal effort for defrag in CPU percentage
# Maximal effort for defrag in CPU percentage
# active-defrag-cycle-max 75