redis的redis.conf文件详解

  1 redis.conf配置文件
  2 
  3 # Redis configuration file example
  4  
  5 # Note on units: when memory size is needed, it is possible to specifiy
  6 # it in the usual form of 1k 5GB 4M and so forth:
  7 #
  8 # 1k => 1000 bytes
  9 # 1kb => 1024 bytes
 10 # 1m => 1000000 bytes
 11 # 1mb => 1024*1024 bytes
 12 # 1g => 1000000000 bytes
 13 # 1gb => 1024*1024*1024 bytes
 14 #
 15 # units are case insensitive so 1GB 1Gb 1gB are all the same.
 16 
 17 ################################## INCLUDES ###################################
 18  
 19 # Include one or more other config files here.  This is useful if you
 20 # have a standard template that goes to all redis server but also need
 21 # to customize a few per-server settings.  Include files can include
 22 # other files, so use this wisely.
 23 #
 24 # include /path/to/local.conf
 25 # include /path/to/other.conf
 26 指定包含其它的配置文件，可以在同一主机上多个Redis实例之间使用同一份配置文件，而同时各个实例又拥有自己的特定配置文件
 27 
 28 ################################ GENERAL  #####################################
 29  
 30 # By default Redis does not run as a daemon. Use ‘yes‘ if you need it.
 31 # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
 32 daemonize no 
 33 Redis默认不是以守护进程的方式运行，可以通过该配置项修改，使用yes启用守护进程
 34  
 35 
 36 # When running daemonized, Redis writes a pid file in /var/run/redis.pid by
 37 # default. You can specify a custom pid file location here.
 38 pidfile /var/run/redis.pid
 39 当Redis以守护进程方式运行时，Redis默认会把pid写入/var/run/redis.pid文件，可以通过pidfile指定
 40 
 41 
 42 # Accept connections on the specified port, default is 6379.
 43 # If port 0 is specified Redis will not listen on a TCP socket.
 44 port 6379
 45 指定Redis监听端口，默认端口为6379
 46 
 47 
 48 # If you want you can bind a single interface, if the bind option is not
 49 # specified all the interfaces will listen for incoming connections.
 50 #
 51 # bind 127.0.0.1
 52 绑定的主机地址
 53 
 54 
 55 # Specify the path for the unix socket that will be used to listen for
 56 # incoming connections. There is no default, so Redis will not listen
 57 # on a unix socket when not specified.
 58 #
 59 # unixsocket /tmp/redis.sock
 60 # unixsocketperm 755
 61  
 62 # Close the connection after a client is idle for N seconds (0 to disable)
 63 timeout 0
 64 当 客户端闲置多长时间后关闭连接，如果指定为0，表示关闭该功能
 65 
 66 
 67 # Set server verbosity to ‘debug‘
 68 # it can be one of:
 69 # debug (a lot of information, useful for development/testing)
 70 # verbose (many rarely useful info, but not a mess like the debug level)
 71 # notice (moderately verbose, what you want in production probably)
 72 # warning (only very important / critical messages are logged)
 73 loglevel verbose
 74 指定日志记录级别，Redis总共支持四个级别：debug、verbose、notice、warning，默认为verbose
 75 
 76 # Specify the log file name. Also ‘stdout‘ can be used to force
 77 # Redis to log on the standard output. Note that if you use standard
 78 # output for logging but daemonize, logs will be sent to /dev/null
 79 logfile stdout
 80 
 81 
 82 日志记录方式，默认为标准输出，如果配置Redis为守护进程方式运行，而这里又配置为日志记录方式为标准输出，则日志将会发送给/dev/null
 83 # To enable logging to the system logger, just set ‘syslog-enabled‘ to yes,
 84 # and optionally update the other syslog parameters to suit your needs.
 85 # syslog-enabled no
 86  
 87 # Specify the syslog identity.
 88 # syslog-ident redis
 89  
 90 # Specify the syslog facility.  Must be USER or between LOCAL0-LOCAL7.
 91 # syslog-facility local0
 92  
 93 # Set the number of databases. The default database is DB 0, you can select
 94 # a different one on a per-connection basis using SELECT <dbid> where
 95 # dbid is a number between 0 and ‘databases‘-1
 96 databases 16
 97 
 98 
 99 设置数据库的数量，默认数据库为0，可以使用SELECT <dbid>命令在连接上指定数据库id
100 ################################ SNAPSHOTTING  #################################
101 #
102 # Save the DB on disk:
103 #
104 #   save <seconds> <changes>
105 #
106 #   Will save the DB if both the given number of seconds and the given
107 #   number of write operations against the DB occurred.
108 #
109 #   In the example below the behaviour will be to save:
110 #   after 900 sec (15 min) if at least 1 key changed
111 #   after 300 sec (5 min) if at least 10 keys changed
112 #   after 60 sec if at least 10000 keys changed
113 #
114 #   Note: you can disable saving at all commenting all the "save" lines.
115  
116 save 900 1
117 save 300 10
118 save 60 10000
119 分别表示900秒（15分钟）内有1个更改，300秒（5分钟）内有10个更改以及60秒内有10000个更改。
120 指定在多长时间内，有多少次更新操作，就将数据同步到数据文件，可以多个条件配合
121 
122 
123 # Compress string objects using LZF when dump .rdb databases?
124 # For default that‘s set to ‘yes‘ as it‘s almost always a win.
125 # If you want to save some CPU in the saving child set it to ‘no‘ but
126 # the dataset will likely be bigger if you have compressible values or keys.
127 rdbcompression yes
128 指定存储至本地数据库时是否压缩数据，默认为yes，Redis采用LZF压缩，如果为了节省CPU时间，可以关闭该选项，但会导致数据库文件变的巨大
129 
130 
131 # The filename where to dump the DB
132 dbfilename dump.rdb
133 指定本地数据库文件名，默认值为dump.rdb
134 
135 
136 # The working directory.
137 #
138 # The DB will be written inside this directory, with the filename specified
139 # above using the ‘dbfilename‘ configuration directive.
140 #
141 # Also the Append Only File will be created inside this directory.
142 #
143 # Note that you must specify a directory here, not a file name.
144 dir ./
145 指定本地数据库存放目录
146 
147 
148 
149 ################################# REPLICATION #################################
150  
151 # Master-Slave replication(主从复制). Use slaveof to make a Redis instance a copy of
152 # another Redis server. Note that the configuration is local to the slave
153 # so for example it is possible to configure the slave to save the DB with a
154 # different interval, or to listen to another port, and so on.
155 #
156 # slaveof <masterip> <masterport>
157 slaveof <masterip> <masterport> 设置当本机为slav服务时，设置master服务的IP地址及端口，在Redis启动时，它会自动从master进行数据同步
158 
159 
160 
161 # If the master is password protected (using the "requirepass" configuration
162 # directive below) it is possible to tell the slave to authenticate before
163 # starting the replication synchronization process, otherwise the master will
164 # refuse the slave request.
165 #
166 # masterauth <master-password>
167 masterauth <master-password> 当master服务设置了密码保护时，slav服务连接master的密码
168 
169 
170 # When a slave lost the connection with the master, or when the replication
171 # is still in progress, the slave can act in two different ways:
172 #
173 # 1) if slave-serve-stale-data is set to ‘yes‘ (the default) the slave will
174 #    still reply to client requests, possibly with out of data data, or the
175 #    data set may just be empty if this is the first synchronization.
176 #
177 # 2) if slave-serve-stale data is set to ‘no‘ the slave will reply with
178 #    an error "SYNC with master in progress" to all the kind of commands
179 #    but to INFO and SLAVEOF.
180 #
181 slave-serve-stale-datayes
182  
183 
184 
185 # Slaves send PINGs to server in a predefined interval. It‘s possible to change
186 # this interval with the repl_ping_slave_period option. The default value is 10
187 # seconds.
188 #
189 # repl-ping-slave-period 10
190  
191 # The following option sets a timeout for both Bulk transfer I/O timeout and
192 # master data or ping response timeout. The default value is 60 seconds.
193 #
194 # It is important to make sure that this value is greater than the value
195 # specified for repl-ping-slave-period otherwise a timeout will be detected
196 # every time there is low traffic between the master and the slave.
197 #
198 # repl-timeout 60
199  
200 ################################## SECURITY ###################################
201  
202 # Require clients to issue AUTH <PASSWORD> before processing any other
203 # commands.  This might be useful in environments in which you do not trust
204 # others with access to the host running redis-server.
205 #
206 # This should stay commented out for backward compatibility and because most
207 # people do not need auth (e.g. they run their own servers).
208 #
209 # Warning: since Redis is pretty fast an outside user can try up to
210 # 150k passwords per second against a good box. This means that you should
211 # use a very strong password otherwise it will be very easy to break.
212 #
213 # requirepass foobared
214  requirepass foobared 设置Redis连接密码，如果配置了连接密码，客户端在连接Redis时需要通过AUTH <password>命令提供密码，默认关闭
215 
216 
217 # Command renaming.
218 #
219 # It is possilbe to change the name of dangerous commands in a shared
220 # environment. For instance the CONFIG command may be renamed into something
221 # of hard to guess so that it will be still available for internal-use
222 # tools but not available for general clients.
223 #
224 # Example:
225 #
226 # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
227 #
228 # It is also possilbe to completely kill a command renaming it into
229 # an empty string:
230 #
231 # rename-command CONFIG ""
232  
233 ################################### LIMITS ####################################
234  
235 # Set the max number of connected clients at the same time. By default there
236 # is no limit, and it‘s up to the number of file descriptors the Redis process
237 # is able to open. The special value ‘0‘ means no limits.
238 # Once the limit is reached Redis will close all the new connections sending
239 # an error ‘max number of clients reached‘.
240 #
241 # maxclients 128
242 maxclients 128 设置同一时间最大客户端连接数，默认无限制，Redis可以同时打开的客户端连接数为Redis进程可以打开的最大文件描述符数，如果设置 maxclients 0，表示不作限制。当客户端连接数到达限制时，Redis会关闭新的连接并向客户端返回max number of clients reached错误信息
243 
244 
245 
246 # Don‘t use more memory than the specified amount of bytes.
247 # When the memory limit is reached Redis will try to remove keys with an
248 # EXPIRE set. It will try to start freeing keys that are going to expire
249 # in little time and preserve keys with a longer time to live.
250 # Redis will also try to remove objects from free lists if possible.
251 #
252 # If all this fails, Redis will start to reply with errors to commands
253 # that will use more memory, like SET, LPUSH, and so on, and will continue
254 # to reply to most read-only commands like GET.
255 #
256 # WARNING: maxmemory can be a good idea mainly if you want to use Redis as a
257 # ‘state‘ server or cache, not as a real DB. When Redis is used as a real
258 # database the memory usage will grow over the weeks, it will be obvious if
259 # it is going to use too much memory in the long run, and you‘ll have the time
260 # to upgrade. With maxmemory after the limit is reached you‘ll start to get
261 # errors for write operations, and this may even lead to DB inconsistency.
262 #
263 # maxmemory <bytes>
264  maxmemory <bytes>指定Redis最大内存限制，Redis在启动时会把数据加载到内存中，达到最大内存后，Redis会先尝试清除已到期或即将到期的Key，当此方法处理 后，仍然到达最大内存设置，将无法再进行写入操作，但仍然可以进行读取操作。Redis新的vm机制，会把Key存放内存，Value会存放在swap区
265 
266 
267 
268 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
269 # is reached? You can select among five behavior:
270 #
271 # volatile-lru -> remove the key with an expire set using an LRU algorithm
272 # allkeys-lru -> remove any key accordingly to the LRU algorithm
273 # volatile-random -> remove a random key with an expire set
274 # allkeys->random -> remove a random key, any key
275 # volatile-ttl -> remove the key with the nearest expire time (minor TTL)
276 # noeviction -> don‘t expire at all, just return an error on write operations
277 #
278 # Note: with all the kind of policies, Redis will return an error on write
279 #       operations, when there are not suitable keys for eviction.
280 #
281 #       At the date of writing this commands are: set setnx setex append
282 #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
283 #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
284 #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
285 #       getset mset msetnx exec sort
286 #
287 # The default is:
288 #
289 # maxmemory-policy volatile-lru
290  
291 # LRU and minimal TTL algorithms are not precise algorithms but approximated
292 # algorithms (in order to save memory), so you can select as well the sample
293 # size to check. For instance for default Redis will check three keys and
294 # pick the one that was used less recently, you can change the sample size
295 # using the following configuration directive.
296 #
297 # maxmemory-samples 3
298  
299 ############################## APPEND ONLY MODE ###############################
300  
301 # By default Redis asynchronously dumps the dataset on disk. If you can live
302 # with the idea that the latest records will be lost if something like a crash
303 # happens this is the preferred way to run Redis. If instead you care a lot
304 # about your data and don‘t want to that a single record can get lost you should
305 # enable the append only mode: when this mode is enabled Redis will append
306 # every write operation received in the file appendonly.aof. This file will
307 # be read on startup in order to rebuild the full dataset in memory.
308 #
309 # Note that you can have both the async dumps and the append only file if you
310 # like (you have to comment the "save" statements above to disable the dumps).
311 # Still if append only mode is enabled Redis will load the data from the
312 # log file at startup ignoring the dump.rdb file.
313 #
314 # IMPORTANT: Check the BGREWRITEAOF to check how to rewrite the append
315 # log file in background when it gets too big.
316  
317 appendonly no
318 appendonly no指定是否在每次更新操作后进行日志记录，Redis在默认情况下是异步的把数据写入磁盘，如果不开启，可能会在断电时导致一段时间内的数据丢失。因为 redis本身同步数据文件是按上面save条件来同步的，所以有的数据会在一段时间内只存在于内存中。默认为no
319 
320 
321 
322 # The name of the append only file (default: "appendonly.aof")
323 # appendfilename appendonly.aof
324  appendfilename appendonly.aof指定更新日志文件名，默认为appendonly.aof
325 # The fsync() call tells the Operating System to actually write data on disk
326 # instead to wait for more data in the output buffer. Some OS will really flush
327 # data on disk, some other OS will just try to do it ASAP.
328 #
329 # Redis supports three different modes:
330 #
331 # no: don‘t fsync, just let the OS flush the data when it wants. Faster.
332 # always: fsync after every write to the append only log . Slow, Safest.
333 # everysec: fsync only if one second passed since the last fsync. Compromise.
334 #
335 # The default is "everysec" that‘s usually the right compromise between
336 # speed and data safety. It‘s up to you to understand if you can relax this to
337 # "no" that will will let the operating system flush the output buffer when
338 # it wants, for better performances (but if you can live with the idea of
339 # some data loss consider the default persistence mode that‘s snapshotting),
340 # or on the contrary, use "always" that‘s very slow but a bit safer than
341 # everysec.
342 #
343 # If unsure, use "everysec".
344  
345 # appendfsync always
346 appendfsync everysec
347 # appendfsync no
348 指定更新日志条件，共有3个可选值：
349 no：表示等操作系统进行数据缓存同步到磁盘（快）
350 always：表示每次更新操作后手动调用fsync()将数据写到磁盘（慢，安全）
351 everysec：表示每秒同步一次（折衷，默认值）
352 
353 
354 
355 # When the AOF fsync policy is set to always or everysec, and a background
356 # saving process (a background save or AOF log background rewriting) is
357 # performing a lot of I/O against the disk, in some Linux configurations
358 # Redis may block too long on the fsync() call. Note that there is no fix for
359 # this currently, as even performing fsync in a different thread will block
360 # our synchronous write(2) call.
361 #
362 # In order to mitigate this problem it‘s possible to use the following option
363 # that will prevent fsync() from being called in the main process while a
364 # BGSAVE or BGREWRITEAOF is in progress.
365 #
366 # This means that while another child is saving the durability of Redis is
367 # the same as "appendfsync none", that in pratical terms means that it is
368 # possible to lost up to 30 seconds of log in the worst scenario (with the
369 # default Linux settings).
370 #
371 # If you have latency problems turn this to "yes". Otherwise leave it as
372 # "no" that is the safest pick from the point of view of durability.
373 no-appendfsync-on-rewrite no
374  
375 # Automatic rewrite of the append only file.
376 # Redis is able to automatically rewrite the log file implicitly calling
377 # BGREWRITEAOF when the AOF log size will growth by the specified percentage.
378 #
379 # This is how it works: Redis remembers the size of the AOF file after the
380 # latest rewrite (or if no rewrite happened since the restart, the size of
381 # the AOF at startup is used).
382 #
383 # This base size is compared to the current size. If the current size is
384 # bigger than the specified percentage, the rewrite is triggered. Also
385 # you need to specify a minimal size for the AOF file to be rewritten, this
386 # is useful to avoid rewriting the AOF file even if the percentage increase
387 # is reached but it is still pretty small.
388 #
389 # Specify a precentage of zero in order to disable the automatic AOF
390 # rewrite feature.
391  
392 auto-aof-rewrite-percentage 100
393 auto-aof-rewrite-min-size 64mb
394  
395 ################################## SLOW LOG ###################################
396  
397 # The Redis Slow Log is a system to log queries that exceeded a specified
398 # execution time. The execution time does not include the I/O operations
399 # like talking with the client, sending the reply and so forth,
400 # but just the time needed to actually execute the command (this is the only
401 # stage of command execution where the thread is blocked and can not serve
402 # other requests in the meantime).
403 #
404 # You can configure the slow log with two parameters: one tells Redis
405 # what is the execution time, in microseconds, to exceed in order for the
406 # command to get logged, and the other parameter is the length of the
407 # slow log. When a new command is logged the oldest one is removed from the
408 # queue of logged commands.
409  
410 # The following time is expressed in microseconds, so 1000000 is equivalent
411 # to one second. Note that a negative number disables the slow log, while
412 # a value of zero forces the logging of every command.
413 slowlog-log-slower-than 10000
414  
415 # There is no limit to this length. Just be aware that it will consume memory.
416 # You can reclaim memory used by the slow log with SLOWLOG RESET.
417 slowlog-max-len 1024
418  
419 ################################ VIRTUAL MEMORY ###############################
420  
421 ### WARNING! Virtual Memory is deprecated in Redis 2.4
422 ### The use of Virtual Memory is strongly discouraged.
423  
424 ### WARNING! Virtual Memory is deprecated in Redis 2.4
425 ### The use of Virtual Memory is strongly discouraged.
426  
427 # Virtual Memory allows Redis to work with datasets bigger than the actual
428 # amount of RAM needed to hold the whole dataset in memory.
429 # In order to do so very used keys are taken in memory while the other keys
430 # are swapped into a swap file, similarly to what operating systems do
431 # with memory pages.
432 #
433 # To enable VM just set ‘vm-enabled‘ to yes, and set the following three
434 # VM parameters accordingly to your needs.
435  
436 vm-enabled no
437 指定是否启用虚拟内存机制，默认值为no，简单的介绍一下，VM机制将数据分页存放，由Redis将访问量较少的页即冷数据swap到磁盘上，访问多的页面由磁盘自动换出到内存中（在后面的文章我会仔细分析Redis的VM机制）
438 
439 
440 
441 
442 # vm-enabled yes
443  
444 # This is the path of the Redis swap file. As you can guess, swap files
445 # can‘t be shared by different Redis instances, so make sure to use a swap
446 # file for every redis process you are running. Redis will complain if the
447 # swap file is already in use.
448 #
449 # The best kind of storage for the Redis swap file (that‘s accessed at random)
450 # is a Solid State Disk (SSD).
451 #
452 # *** WARNING *** if you are using a shared hosting the default of putting
453 # the swap file under /tmp is not secure. Create a dir with access granted
454 # only to Redis user and configure Redis to create the swap file there.
455 vm-swap-file /tmp/redis.swap
456 虚拟内存文件路径，默认值为/tmp/redis.swap，不可多个Redis实例共享
457 
458 
459 
460 # vm-max-memory configures the VM to use at max the specified amount of
461 # RAM. Everything that deos not fit will be swapped on disk *if* possible, that
462 # is, if there is still enough contiguous space in the swap file.
463 #
464 # With vm-max-memory 0 the system will swap everything it can. Not a good
465 # default, just specify the max amount of RAM you can in bytes, but it‘s
466 # better to leave some margin. For instance specify an amount of RAM
467 # that‘s more or less between 60 and 80% of your free RAM.
468 vm-max-memory 0
469 将所有大于vm-max-memory的数据存入虚拟内存,无论vm-max-memory设置多小,所有索引数据都是内存存储的(Redis的索引数据 就是keys),也就是说,当vm-max-memory设置为0的时候,其实是所有value都存在于磁盘。默认值为0
470 
471 
472 
473 # Redis swap files is split into pages. An object can be saved using multiple
474 # contiguous pages, but pages can‘t be shared between different objects.
475 # So if your page is too big, small objects swapped out on disk will waste
476 # a lot of space. If you page is too small, there is less space in the swap
477 # file (assuming you configured the same number of total swap file pages).
478 #
479 # If you use a lot of small objects, use a page size of 64 or 32 bytes.
480 # If you use a lot of big objects, use a bigger page size.
481 # If unsure, use the default :)
482 vm-page-size 32
483 Redis swap文件分成了很多的page，一个对象可以保存在多个page上面，但一个page上不能被多个对象共享，vm-page-size是要根据存储的 数据大小来设定的，作者建议如果存储很多小对象，page大小最好设置为32或者64bytes；如果存储很大大对象，则可以使用更大的page，如果不 确定，就使用默认值
484 
485 
486 
487 # Number of total memory pages in the swap file.
488 # Given that the page table (a bitmap of free/used pages) is taken in memory,
489 # every 8 pages on disk will consume 1 byte of RAM.
490 #
491 # The total swap size is vm-page-size * vm-pages
492 #
493 # With the default of 32-bytes memory pages and 134217728 pages Redis will
494 # use a 4 GB swap file, that will use 16 MB of RAM for the page table.
495 #
496 # It‘s better to use the smallest acceptable value for your application,
497 # but the default is large in order to work in most conditions.
498 vm-pages 134217728
499 设置swap文件中的page数量，由于页表（一种表示页面空闲或使用的bitmap）是在放在内存中的，，在磁盘上每8个pages将消耗1byte的内存。
500 
501 
502 
503 # Max number of VM I/O threads running at the same time.
504 # This threads are used to read/write data from/to swap file, since they
505 # also encode and decode objects from disk to memory or the reverse, a bigger
506 # number of threads can help with big objects even if they can‘t help with
507 # I/O itself as the physical device may not be able to couple with many
508 # reads/writes operations at the same time.
509 #
510 # The special value of 0 turn off threaded I/O and enables the blocking
511 # Virtual Memory implementation.
512 vm-max-threads 4
513 设置访问swap文件的线程数,最好不要超过机器的核数,如果设置为0,那么所有对swap文件的操作都是串行的，可能会造成比较长时间的延迟。默认值为4
514 
515 
516 
517 ############################### ADVANCED CONFIG ###############################
518  
519 # Hashes are encoded in a special way (much more memory efficient) when they
520 # have at max a given numer of elements, and the biggest element does not
521 # exceed a given threshold. You can configure this limits with the following
522 # configuration directives.
523 hash-max-zipmap-entries 512
524 hash-max-zipmap-value 64
525 指定在超过一定的数量或者最大的元素超过某一临界值时，采用一种特殊的哈希算法
526 
527 
528 
529 # Similarly to hashes, small lists are also encoded in a special way in order
530 # to save a lot of space. The special representation is only used when
531 # you are under the following limits:
532 list-max-ziplist-entries 512
533 list-max-ziplist-value 64
534  
535 # Sets have a special encoding in just one case: when a set is composed
536 # of just strings that happens to be integers in radix 10 in the range
537 # of 64 bit signed integers.
538 # The following configuration setting sets the limit in the size of the
539 # set in order to use this special memory saving encoding.
540 set-max-intset-entries 512
541  
542 # Similarly to hashes and lists, sorted sets are also specially encoded in
543 # order to save a lot of space. This encoding is only used when the length and
544 # elements of a sorted set are below the following limits:
545 zset-max-ziplist-entries 128
546 zset-max-ziplist-value 64
547  
548 # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
549 # order to help rehashing the main Redis hash table (the one mapping top-level
550 # keys to values). The hash table implementation redis uses (see dict.c)
551 # performs a lazy rehashing: the more operation you run into an hash table
552 # that is rhashing, the more rehashing "steps" are performed, so if the
553 # server is idle the rehashing is never complete and some more memory is used
554 # by the hash table.
555 #
556 # The default is to use this millisecond 10 times every second in order to
557 # active rehashing the main dictionaries, freeing memory when possible.
558 #
559 # If unsure:
560 # use "activerehashing no" if you have hard latency requirements and it is
561 # not a good thing in your environment that Redis can reply form time to time
562 # to queries with 2 milliseconds delay.
563 #
564 # use "activerehashing yes" if you don‘t have such hard requirements but
565 # want to free memory asap when possible.
566 activerehashing yes
567