Redis-specific parameters

If you do not specify a parameter group for your Redis cluster, then a default parameter group appropriate to your engine version will be used. You can't change the values of any parameters in the default parameter group. However, you can create a custom parameter group and assign it to your cluster at any time as long as the values of conditionally modifiable parameters are the same in both parameter groups. For more information, see Creating a parameter group.

Redis 7 parameter changes

Parameter group family: redis7

Redis 7 default parameter groups are as follows:

• default.redis7 – Use this parameter group, or one derived from it, for Redis (cluster mode disabled) clusters and replication groups.

• default.redis7.cluster.on – Use this parameter group, or one derived from it, for Redis (cluster mode enabled) clusters and replication groups.

Parameters added in Redis 7 are as follows.

Name	Details	Description
cluster-allow-pubsubshard-when-down	Permitted values: yes, no Default: yes Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	When set to the default of yes, allows nodes to serve pubsub shard traffic while the cluster is in a down state, as long as it believes it owns the slots.
cluster-preferred-endpoint-type	Permitted values: ip, tls-dynamic Default: tls-dynamic Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	This value controls what endpoint is returned for MOVED/ASKING requests as well as the endpoint field for CLUSTER SLOTS and CLUSTER SHARDS. When the value is set to ip, the node will advertise its ip address. When the value is set to tls-dynamic, the node will advertise a hostname when encryption-in-transit is enabled and an ip address otherwise.
latency-tracking	Permitted values: yes, no Default: no Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	When set to yes tracks the per command latencies and enables exporting the percentile distribution via the INFO latency statistics command, and cumulative latency distributions (histograms) via the LATENCY command.
hash-max-listpack-entries	Permitted values: 0+ Default: 512 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	The maximum number of hash entries in order for the dataset to be compressed.
hash-max-listpack-value	Permitted values: 0+ Default: 64 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	The threshold of biggest hash entries in order for the dataset to be compressed.
zset-max-listpack-entries	Permitted values: 0+ Default: 128 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	The maximum number of sorted set entries in order for the dataset to be compressed.
zset-max-listpack-value	Permitted values: 0+ Default: 64 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	The threshold of biggest sorted set entries in order for the dataset to be compressed.

Parameters changed in Redis 7 are as follows.

Name	Details	Description
activerehashing	Modifiable: no. In Redis 7, this parameter is hidden and enabled by default. In order to disable it, you need to create a support case.	Modifiable was yes.

Parameters removed in Redis 7 are as follows.

Name	Details	Description
hash-max-ziplist-entries	Permitted values: 0+ Default: 512 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	Use listpack instead of ziplist for representing small hash encoding
hash-max-ziplist-value	Permitted values: 0+ Default: 64 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	Use listpack instead of ziplist for representing small hash encoding
zset-max-ziplist-entries	Permitted values: 0+ Default: 128 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	Use listpack instead of ziplist for representing small hash encoding.
zset-max-ziplist-value	Permitted values: 0+ Default: 64 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	Use listpack instead of ziplist for representing small hash encoding.
list-max-ziplist-size	Permitted values: Default: -2 Type: integer Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster.	The number of entries allowed per internal list node.

Redis 6.x parameter changes

Parameter group family: redis6.x

Redis 6.x default parameter groups are as follows:

• default.redis6.x – Use this parameter group, or one derived from it, for Redis (cluster mode disabled) clusters and replication groups.

• default.redis6.x.cluster.on – Use this parameter group, or one derived from it, for Redis (cluster mode enabled) clusters and replication groups.

Note

In Redis engine version 6.2, when the r6gd node family was introduced for use with Data tiering, only noeviction, volatile-lru and allkeys-lru max-memory policies are supported with r6gd node types.

For more information, see ElastiCache for Redis version 6.2 (enhanced) and ElastiCache for Redis version 6.0 (enhanced).

Parameters added in Redis 6.x are as follows.

Name	Details	Description
acl-pubsub-default (added in 6.2)	Permitted values: resetchannels, allchannels Default: allchannels Type: string Modifiable: Yes Changes take effect: The existing Redis users associated to the cluster will continue to have existing permissions. Either update the users or reboot the cluster to update the existing Redis users.	Default pubsub channel permissions for ACL users deployed to this cluster.
cluster-allow-reads-when-down (added in 6.0)	Default: no Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	When set to yes, a Redis (cluster mode enabled) replication group continues to process read commands even when a node is not able to reach a quorum of primaries. When set to the default of no, the replication group rejects all commands. We recommend setting this value to yes if you are using a cluster with fewer than three node groups or your application can safely handle stale reads.
tracking-table-max-keys (added in 6.0)	Default: 1,000,000 Type: number Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	To assist client-side caching, Redis supports tracking which clients have accessed which keys. When the tracked key is modified, invalidation messages are sent to all clients to notify them their cached values are no longer valid. This value enables you to specify the upper bound of this table. After this parameter value is exceeded, clients are sent invalidation randomly. This value should be tuned to limit memory usage while still keeping track of enough keys. Keys are also invalidated under low memory conditions.
acllog-max-len (added in 6.0)	Default: 128 Type: number Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	This value corresponds to the max number of entries in the ACL log.
active-expire-effort (added in 6.0)	Default: 1 Type: number Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	Redis deletes keys that have exceeded their time to live by two mechanisms. In one, a key is accessed and is found to be expired. In the other, a periodic job samples keys and causes those that have exceeded their time to live to expire. This parameter defines the amount of effort that Redis uses to expire items in the periodic job. The default value of 1 tries to avoid having more than 10 percent of expired keys still in memory. It also tries to avoid consuming more than 25 percent of total memory and to add latency to the system. You can increase this value up to 10 to increase the amount of effort spent on expiring keys. The tradeoff is higher CPU and potentially higher latency. We recommend a value of 1 unless you are seeing high memory usage and can tolerate an increase in CPU utilization.
lazyfree-lazy-user-del (added in 6.0)	Default: no Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	When the value is set to yes, the DEL command acts the same as UNLINK.

Parameters removed in Redis 6.x are as follows.

Name	Details	Description
lua-replicate-commands	Permitted values: yes/no Default: yes Type: boolean Modifiable: Yes Changes take effect: Immediately	Always enable Lua effect replication or not in Lua scripts

Redis 5.0.3 parameter changes

Parameter group family: redis5.0

Redis 5.0 default parameter groups

• default.redis5.0 – Use this parameter group, or one derived from it, for Redis (cluster mode disabled) clusters and replication groups.

• default.redis5.0.cluster.on – Use this parameter group, or one derived from it, for Redis (cluster mode enabled) clusters and replication groups.

Parameters added in Redis 5.0.3
Name	Details	Description
rename-commands	Default: none Type: string Modifiable: Yes Changes take effect: Immediately across all nodes in the cluster	A space-separated list of renamed Redis commands. The following is a restricted list of commands available for renaming: APPEND AUTH BITCOUNT BITFIELD BITOP BITPOS BLPOP BRPOP BRPOPLPUSH BZPOPMIN BZPOPMAX CLIENT CLUSTER COMMAND DBSIZE DECR DECRBY DEL DISCARD DUMP ECHO EVAL EVALSHA EXEC EXISTS EXPIRE EXPIREAT FLUSHALL FLUSHDB GEOADD GEOHASH GEOPOS GEODIST GEORADIUS GEORADIUSBYMEMBER GET GETBIT GETRANGE GETSET HDEL HEXISTS HGET HGETALL HINCRBY HINCRBYFLOAT HKEYS HLEN HMGET HMSET HSET HSETNX HSTRLEN HVALS INCR INCRBY INCRBYFLOAT INFO KEYS LASTSAVE LINDEX LINSERT LLEN LPOP LPUSH LPUSHX LRANGE LREM LSET LTRIM MEMORY MGET MONITOR MOVE MSET MSETNX MULTI OBJECT PERSIST PEXPIRE PEXPIREAT PFADD PFCOUNT PFMERGE PING PSETEX PSUBSCRIBE PUBSUB PTTL PUBLISH PUNSUBSCRIBE RANDOMKEY READONLY READWRITE RENAME RENAMENX RESTORE ROLE RPOP RPOPLPUSH RPUSH RPUSHX SADD SCARD SCRIPT SDIFF SDIFFSTORE SELECT SET SETBIT SETEX SETNX SETRANGE SINTER SINTERSTORE SISMEMBER SLOWLOG SMEMBERS SMOVE SORT SPOP SRANDMEMBER SREM STRLEN SUBSCRIBE SUNION SUNIONSTORE SWAPDB TIME TOUCH TTL TYPE UNSUBSCRIBE UNLINK UNWATCH WAIT WATCH ZADD ZCARD ZCOUNT ZINCRBY ZINTERSTORE ZLEXCOUNT ZPOPMAX ZPOPMIN ZRANGE ZRANGEBYLEX ZREVRANGEBYLEX ZRANGEBYSCORE ZRANK ZREM ZREMRANGEBYLEX ZREMRANGEBYRANK ZREMRANGEBYSCORE ZREVRANGE ZREVRANGEBYSCORE ZREVRANK ZSCORE ZUNIONSTORE SCAN SSCAN HSCAN ZSCAN XINFO XADD XTRIM XDEL XRANGE XREVRANGE XLEN XREAD XGROUP XREADGROUP XACK XCLAIM XPENDING GEORADIUS_RO GEORADIUSBYMEMBER_RO LOLWUT XSETID SUBSTR

For more information, see ElastiCache for Redis version 5.0.6 (enhanced).

Redis 5.0.0 parameter changes

Parameter group family: redis5.0

Redis 5.0 default parameter groups

• default.redis5.0 – Use this parameter group, or one derived from it, for Redis (cluster mode disabled) clusters and replication groups.

• default.redis5.0.cluster.on – Use this parameter group, or one derived from it, for Redis (cluster mode enabled) clusters and replication groups.

Parameters added in Redis 5.0
Name	Details	Description
stream-node-max-bytes	Permitted values: 0+ Default: 4096 Type: integer Modifiable: Yes Changes take effect: Immediately	The stream data structure is a radix tree of nodes that encode multiple items inside. Use this configuration to specify the maximum size of a single node in radix tree in Bytes. If set to 0, the size of the tree node is unlimited.
stream-node-max-entries	Permitted values: 0+ Default: 100 Type: integer Modifiable: Yes Changes take effect: Immediately	The stream data structure is a radix tree of nodes that encode multiple items inside. Use this configuration to specify the maximum number of items a single node can contain before switching to a new node when appending new stream entries. If set to 0, the number of items in the tree node is unlimited
active-defrag-max-scan-fields	Permitted values: 1 to 1000000 Default: 1000 Type: integer Modifiable: Yes Changes take effect: Immediately	Maximum number of set/hash/zset/list fields that will be processed from the main dictionary scan
lua-replicate-commands	Permitted values: yes/no Default: yes Type: boolean Modifiable: Yes Changes take effect: Immediately	Always enable Lua effect replication or not in Lua scripts
replica-ignore-maxmemory	Default: yes Type: boolean Modifiable: No	Determines if replica ignores maxmemory setting by not evicting items independent from the primary

Redis has renamed several parameters in engine version 5.0 in response to community feedback. For more information, see What's New in Redis 5?. The following table lists the new names and how they map to previous versions.

Parameters renamed in Redis 5.0
Name	Details	Description
replica-lazy-flush	Default: yes Type: boolean Modifiable: No Former name: slave-lazy-flush	Performs an asynchronous flushDB during replica sync.
client-output-buffer-limit-replica-hard-limit	Default: For values see Redis node-type specific parameters Type: integer Modifiable: No Former name: client-output-buffer-limit-slave-hard-limit	For Redis read replicas: If a client's output buffer reaches the specified number of bytes, the client will be disconnected.
client-output-buffer-limit-replica-soft-limit	Default: For values see Redis node-type specific parameters Type: integer Modifiable: No Former name: client-output-buffer-limit-slave-soft-limit	For Redis read replicas: If a client's output buffer reaches the specified number of bytes, the client will be disconnected, but only if this condition persists for client-output-buffer-limit-replica-soft-seconds.
client-output-buffer-limit-replica-soft-seconds	Default: 60 Type: integer Modifiable: No Former name: client-output-buffer-limit-slave-soft-seconds	For Redis read replicas: If a client's output buffer remains at client-output-buffer-limit-replica-soft-limit bytes for longer than this number of seconds, the client will be disconnected.
replica-allow-chaining	Default: no Type: string Modifiable: No Former name: slave-allow-chaining	Determines whether a read replica in Redis can have read replicas of its own.
min-replicas-to-write	Default: 0 Type: integer Modifiable: Yes Former name: min-slaves-to-write Changes Take Effect: Immediately	The minimum number of read replicas which must be available in order for the primary node to accept writes from clients. If the number of available replicas falls below this number, then the primary node will no longer accept write requests. If either this parameter or min-replicas-max-lag is 0, then the primary node will always accept writes requests, even if no replicas are available.
min-replicas-max-lag	Default: 10 Type: integer Modifiable: Yes Former name: min-slaves-max-lag Changes Take Effect: Immediately	The number of seconds within which the primary node must receive a ping request from a read replica. If this amount of time passes and the primary does not receive a ping, then the replica is no longer considered available. If the number of available replicas drops below min-replicas-to-write, then the primary will stop accepting writes at that point. If either this parameter or min-replicas-to-write is 0, then the primary node will always accept write requests, even if no replicas are available.
close-on-replica-write	Default: yes Type: boolean Modifiable: Yes Former name: close-on-slave-write Changes Take Effect: Immediately	If enabled, clients who attempt to write to a read-only replica will be disconnected.

Parameters removed in Redis 5.0
Name	Details	Description
repl-timeout	Default: 60 Modifiable: No	Parameter is not available in this version.

Redis 4.0.10 parameter changes

Parameter group family: redis4.0

Redis 4.0.x default parameter groups

• default.redis4.0 – Use this parameter group, or one derived from it, for Redis (cluster mode disabled) clusters and replication groups.

• default.redis4.0.cluster.on – Use this parameter group, or one derived from it, for Redis (cluster mode enabled) clusters and replication groups.

Parameters changed in Redis 4.0.10
Name	Details	Description
maxmemory-policy	Permitted values: allkeys-lru, volatile-lru, allkeys-lfu, volatile-lfu, allkeys-random, volatile-random, volatile-ttl, noeviction Default: volatile-lru Type: string Modifiable: Yes Changes take place: immediately	maxmemory-policy was added in version 2.6.13. In version 4.0.10 two new permitted values are added: allkeys-lfu, which will evict any key using approximated LFU, and volatile-lfu, which will evict using approximated LFU among the keys with an expire set. In version 6.2, when the r6gd node family was introduced for use with data-tiering, only noeviction, volatile-lru and allkeys-lru max-memory policies are supported with r6gd node types.

Parameters added in Redis 4.0.10
Name	Details	Description
Async deletion parameters
lazyfree-lazy-eviction	Permitted values: yes/no Default: no Type: boolean Modifiable: Yes Changes take place: immediately	Performs an asynchronous delete on evictions.
lazyfree-lazy-expire	Permitted values: yes/no Default: no Type: boolean Modifiable: Yes Changes take place: immediately	Performs an asynchronous delete on expired keys.
lazyfree-lazy-server-del	Permitted values: yes/no Default: no Type: boolean Modifiable: Yes Changes take place: immediately	Performs an asynchronous delete for commands which update values.
slave-lazy-flush	Permitted values: N/A Default: no Type: boolean Modifiable: No Changes take place: N/A	Performs an asynchronous flushDB during slave sync.
LFU parameters
lfu-log-factor	Permitted values: any integer > 0 Default: 10 Type: integer Modifiable: Yes Changes take place: immediately	Set the log factor, which determines the number of key hits to saturate the key counter.
lfu-decay-time	Permitted values: any integer Default: 1 Type: integer Modifiable: Yes Changes take place: immediately	The amount of time in minutes to decrement the key counter.
Active defragmentation parameters
activedefrag	Permitted values: yes/no Default: no Type: boolean Modifiable: Yes Changes take place: immediately	Enabled active defragmentation.
active-defrag-ignore-bytes	Permitted values: 10485760-104857600 Default: 104857600 Type: integer Modifiable: Yes Changes take place: immediately	Minimum amount of fragmentation waste to start active defrag.
active-defrag-threshold-lower	Permitted values: 1-100 Default: 10 Type: integer Modifiable: Yes Changes take place: immediately	Minimum percentage of fragmentation to start active defrag.
active-defrag-threshold-upper	Permitted values: 1-100 Default: 100 Type: integer Modifiable: Yes Changes take place: immediately	Maximum percentage of fragmentation at which we use maximum effort.
active-defrag-cycle-min	Permitted values: 1-75 Default: 25 Type: integer Modifiable: Yes Changes take place: immediately	Minimal effort for defrag in CPU percentage.
active-defrag-cycle-max	Permitted values: 1-75 Default: 75 Type: integer Modifiable: Yes Changes take place: immediately	Maximal effort for defrag in CPU percentage.
Client output buffer parameters
client-query-buffer-limit	Permitted values: 1048576-1073741824 Default: 1073741824 Type: integer Modifiable: Yes Changes take place: immediately	Max size of a single client query buffer.
proto-max-bulk-len	Permitted values: 1048576-536870912 Default: 536870912 Type: integer Modifiable: Yes Changes take place: immediately	Max size of a single element request.

Redis 3.2.10 parameter changes

Parameter group family: redis3.2

ElastiCache for Redis 3.2.10 there are no additional parameters supported.

Redis 3.2.6 parameter changes

Parameter group family: redis3.2

For Redis 3.2.6 there are no additional parameters supported.

Redis 3.2.4 parameter changes

Parameter group family: redis3.2

Beginning with Redis 3.2.4 there are two default parameter groups.

• default.redis3.2 – When running Redis 3.2.4, specify this parameter group or one derived from it, if you want to create a Redis (cluster mode disabled) replication group and still use the additional features of Redis 3.2.4.

• default.redis3.2.cluster.on – Specify this parameter group or one derived from it, when you want to create a Redis (cluster mode enabled) replication group.

Topics

• New parameters for Redis 3.2.4
• Parameters changed in Redis 3.2.4 (enhanced)

New parameters for Redis 3.2.4

Parameter group family: redis3.2

For Redis 3.2.4 the following additional parameters are supported.

Name	Details	Description
list-max-ziplist-size	Default: -2 Type: integer Modifiable: No	Lists are encoded in a special way to save space. The number of entries allowed per internal list node can be specified as a fixed maximum size or a maximum number of elements. For a fixed maximum size, use -5 through -1, meaning: -5: max size: 64 Kb - not recommended for normal workloads -4: max size: 32 Kb - not recommended -3: max size: 16 Kb - not recommended -2: max size: 8 Kb - recommended -1: max size: 4 Kb - recommended Positive numbers mean store up to exactly that number of elements per list node.
list-compress-depth	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Lists may also be compressed. Compress depth is the number of quicklist ziplist nodes from each side of the list to exclude from compression. The head and tail of the list are always uncompressed for fast push and pop operations. Settings are: 0: Disable all compression. 1: Start compressing with the 1st node in from the head and tail. [head]->node->node->...->node->[tail] All nodes except [head] and [tail] compress. 2: Start compressing with the 2nd node in from the head and tail. [head]->[next]->node->node->...->node->[prev]->[tail] [head], [next], [prev], [tail] do not compress. All other nodes compress. Etc.
cluster-enabled	Default: no/yes * Type: string Modifiable: No	Indicates whether this is a Redis (cluster mode enabled) replication group in cluster mode (yes) or a Redis (cluster mode enabled) replication group in non-cluster mode (no). Redis (cluster mode enabled) replication groups in cluster mode can partition their data across up to 500 node groups. * Redis 3.2.x has two default parameter groups. default.redis3.2 – default value no. default.redis3.2.cluster.on – default value yes. .
cluster-require-full-coverage	Default: no Type: boolean Modifiable: yes Changes Take Effect: Immediately	When set to yes, Redis (cluster mode enabled) nodes in cluster mode stop accepting queries if they detect there is at least one hash slot uncovered (no available node is serving it). This way if the cluster is partially down, the cluster becomes unavailable. It automatically becomes available again as soon as all the slots are covered again. However, sometimes you want the subset of the cluster which is working to continue to accept queries for the part of the key space that is still covered. To do so, just set the cluster-require-full-coverage option to no.
hll-sparse-max-bytes	Default: 3000 Type: integer Modifiable: Yes Changes Take Effect: Immediately	HyperLogLog sparse representation bytes limit. The limit includes the 16 byte header. When a HyperLogLog using the sparse representation crosses this limit, it is converted into the dense representation. A value greater than 16000 is not recommended, because at that point the dense representation is more memory efficient. We recommend a value of about 3000 to have the benefits of the space-efficient encoding without slowing down PFADD too much, which is O(N) with the sparse encoding. The value can be raised to ~10000 when CPU is not a concern, but space is, and the data set is composed of many HyperLogLogs with cardinality in the 0 - 15000 range.
reserved-memory-percent	Default: 25 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The percent of a node's memory reserved for nondata use. By default, the Redis data footprint grows until it consumes all of the node's memory. If this occurs, then node performance will likely suffer due to excessive memory paging. By reserving memory, you can set aside some of the available memory for non-Redis purposes to help reduce the amount of paging. This parameter is specific to ElastiCache, and is not part of the standard Redis distribution. For more information, see reserved-memory and Managing Reserved Memory.

Parameters changed in Redis 3.2.4 (enhanced)

Parameter group family: redis3.2

For Redis 3.2.4 the following parameters were changed.

Name	Details	Change
activerehashing	Modifiable: Yes if the parameter group is not associated with any cache clusters. Otherwise, no.	Modifiable was No.
databases	Modifiable: Yes if the parameter group is not associated with any cache clusters. Otherwise, no.	Modifiable was No.
appendonly	Default: off Modifiable: No	If you want to upgrade from an earlier Redis version, you must first turn appendonly off.
appendfsync	Default: off Modifiable: No	If you want to upgrade from an earlier Redis version, you must first turn appendfsync off.
repl-timeout	Default: 60 Modifiable: No	Is now unmodifiable with a default of 60.
tcp-keepalive	Default: 300	Default was 0.
list-max-ziplist-entries		Parameter is no longer available.
list-max-ziplist-value		Parameter is no longer available.

Redis 2.8.24 (enhanced) added parameters

Parameter group family: redis2.8

For Redis 2.8.24 there are no additional parameters supported.

Redis 2.8.23 (enhanced) added parameters

Parameter group family: redis2.8

For Redis 2.8.23 the following additional parameter is supported.

Name	Details	Description
close-on-slave-write	Default: yes Type: string (yes/no) Modifiable: Yes Changes Take Effect: Immediately	If enabled, clients who attempt to write to a read-only replica will be disconnected.

How close-on-slave-write works

The close-on-slave-write parameter is introduced by Amazon ElastiCache to give you more control over how your cluster responds when a primary node and a read replica node swap roles due to promoting a read replica to primary.

If the read-replica cluster is promoted to primary for any reason other than a Multi-AZ enabled replication group failing over, the client will continue trying to write to endpoint A. Because endpoint A is now the endpoint for a read-replica, these writes will fail. This is the behavior for Redis before ElastiCache introducing close-on-replica-write and the behavior if you disable close-on-replica-write.

With close-on-replica-write enabled, any time a client attempts to write to a read-replica, the client connection to the cluster is closed. Your application logic should detect the disconnection, check the DNS table, and reconnect to the primary endpoint, which now would be endpoint B.

When you might disable close-on-replica-write

If disabling close-on-replica-write results in writes to the failing cluster, why disable close-on-replica-write?

As previously mentioned, with close-on-replica-write enabled, any time a client attempts to write to a read-replica the client connection to the cluster is closed. Establishing a new connection to the node takes time. Thus, disconnecting and reconnecting as a result of a write request to the replica also affects the latency of read requests that are served through the same connection. This effect remains in place until a new connection is established. If your application is especially read-heavy or very latency-sensitive, you might keep your clients connected to avoid degrading read performance.

Redis 2.8.22 (enhanced) added parameters

Parameter group family: redis2.8

For Redis 2.8.22 there are no additional parameters supported.

Important

• Beginning with Redis version 2.8.22, repl-backlog-size applies to the primary cluster as well as to replica clusters.

• Beginning with Redis version 2.8.22, the repl-timeout parameter is not supported. If it is changed, ElastiCache will overwrite with the default (60s), as we do with appendonly.

The following parameters are no longer supported.

• appendonly

• appendfsync

• repl-timeout

Redis 2.8.21 added parameters

Parameter group family: redis2.8

For Redis 2.8.21, there are no additional parameters supported.

Redis 2.8.19 added parameters

Parameter group family: redis2.8

For Redis 2.8.19 there are no additional parameters supported.

Redis 2.8.6 added parameters

Parameter group family: redis2.8

For Redis 2.8.6 the following additional parameters are supported.

Name	Details	Description
min-slaves-max-lag	Default: 10 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The number of seconds within which the primary node must receive a ping request from a read replica. If this amount of time passes and the primary does not receive a ping, then the replica is no longer considered available. If the number of available replicas drops below min-slaves-to-write, then the primary will stop accepting writes at that point. If either this parameter or min-slaves-to-write is 0, then the primary node will always accept writes requests, even if no replicas are available.
min-slaves-to-write	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The minimum number of read replicas which must be available in order for the primary node to accept writes from clients. If the number of available replicas falls below this number, then the primary node will no longer accept write requests. If either this parameter or min-slaves-max-lag is 0, then the primary node will always accept writes requests, even if no replicas are available.
notify-keyspace-events	Default: (an empty string) Type: string Modifiable: Yes Changes Take Effect: Immediately	The types of keyspace events that Redis can notify clients of. Each event type is represented by a single letter: K — Keyspace events, published with a prefix of __keyspace@<db>__ E — Key-event events, published with a prefix of __keyevent@<db>__ g — Generic, non-specific commands such as DEL, EXPIRE, RENAME, etc. $ — String commands l — List commands s — Set commands h — Hash commands z — Sorted set commands x — Expired events (events generated every time a key expires) e — Evicted events (events generated when a key is evicted for maxmemory) A — An alias for g$lshzxe You can have any combination of these event types. For example, AKE means that Redis can publish notifications of all event types. Do not use any characters other than those listed above; attempts to do so will result in error messages. By default, this parameter is set to an empty string, meaning that keyspace event notification is disabled.
repl-backlog-size	Default: 1048576 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The size, in bytes, of the primary node backlog buffer. The backlog is used for recording updates to data at the primary node. When a read replica connects to the primary, it attempts to perform a partial sync (psync), where it applies data from the backlog to catch up with the primary node. If the psync fails, then a full sync is required. The minimum value for this parameter is 16384. Note Beginning with Redis 2.8.22, this parameter applies to the primary cluster as well as the read replicas.
repl-backlog-ttl	Default: 3600 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The number of seconds that the primary node will retain the backlog buffer. Starting from the time the last replica node disconnected, the data in the backlog will remain intact until repl-backlog-ttl expires. If the replica has not connected to the primary within this time, then the primary will release the backlog buffer. When the replica eventually reconnects, it will have to perform a full sync with the primary. If this parameter is set to 0, then the backlog buffer will never be released.
repl-timeout	Default: 60 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Represents the timeout period, in seconds, for: Bulk data transfer during synchronization, from the read replica's perspective Primary node timeout from the replica's perspective Replica timeout from the primary node's perspective

Redis 2.6.13 parameters

Parameter group family: redis2.6

Redis 2.6.13 was the first version of Redis supported by ElastiCache. The following table shows the Redis 2.6.13 parameters that ElastiCache supports.

Name	Details	Description
activerehashing	Default: yes Type: string (yes/no) Modifiable: Yes Changes take place: At Creation	Determines whether to enable Redis' active rehashing feature. The main hash table is rehashed ten times per second; each rehash operation consumes 1 millisecond of CPU time. This value is set when you create the parameter group. When assigning a new parameter group to a cluster, this value must be the same in both the old and new parameter groups.
appendonly	Default: no Type: string Modifiable: Yes Changes Take Effect: Immediately	Enables or disables Redis' append only file feature (AOF). AOF captures any Redis commands that change data in the cache, and is used to recover from certain node failures. The default value is no, meaning AOF is turned off. Set this parameter to yes to enable AOF. For more information, see Mitigating Failures. Note Append Only Files (AOF) is not supported for cache.t1.micro and cache.t2.* nodes. For nodes of this type, the appendonly parameter value is ignored. Note For Multi-AZ replication groups, AOF is not allowed.
appendfsync	Default: everysec Type: string Modifiable: Yes Changes Take Effect: Immediately	When appendonly is set to yes, controls how often the AOF output buffer is written to disk: no — the buffer is flushed to disk on an as-needed basis. everysec — the buffer is flushed once per second. This is the default. always — the buffer is flushed every time that data in the cluster is modified. Appendfsync is not supported for versions 2.8.22 and later.
client-output-buffer-limit-normal-hard-limit	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	If a client's output buffer reaches the specified number of bytes, the client will be disconnected. The default is zero (no hard limit).
client-output-buffer-limit-normal-soft-limit	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	If a client's output buffer reaches the specified number of bytes, the client will be disconnected, but only if this condition persists for client-output-buffer-limit-normal-soft-seconds. The default is zero (no soft limit).
client-output-buffer-limit-normal-soft-seconds	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	If a client's output buffer remains at client-output-buffer-limit-normal-soft-limit bytes for longer than this number of seconds, the client will be disconnected. The default is zero (no time limit).
client-output-buffer-limit-pubsub-hard-limit	Default: 33554432 Type: integer Modifiable: Yes Changes Take Effect: Immediately	For Redis publish/subscribe clients: If a client's output buffer reaches the specified number of bytes, the client will be disconnected.
client-output-buffer-limit-pubsub-soft-limit	Default: 8388608 Type: integer Modifiable: Yes Changes Take Effect: Immediately	For Redis publish/subscribe clients: If a client's output buffer reaches the specified number of bytes, the client will be disconnected, but only if this condition persists for client-output-buffer-limit-pubsub-soft-seconds.
client-output-buffer-limit-pubsub-soft-seconds	Default: 60 Type: integer Modifiable: Yes Changes Take Effect: Immediately	For Redis publish/subscribe clients: If a client's output buffer remains at client-output-buffer-limit-pubsub-soft-limit bytes for longer than this number of seconds, the client will be disconnected.
client-output-buffer-limit-slave-hard-limit	Default: For values see Redis node-type specific parameters Type: integer Modifiable: No	For Redis read replicas: If a client's output buffer reaches the specified number of bytes, the client will be disconnected.
client-output-buffer-limit-slave-soft-limit	Default: For values see Redis node-type specific parameters Type: integer Modifiable: No	For Redis read replicas: If a client's output buffer reaches the specified number of bytes, the client will be disconnected, but only if this condition persists for client-output-buffer-limit-slave-soft-seconds.
client-output-buffer-limit-slave-soft-seconds	Default: 60 Type: integer Modifiable: No	For Redis read replicas: If a client's output buffer remains at client-output-buffer-limit-slave-soft-limit bytes for longer than this number of seconds, the client will be disconnected.
databases	Default: 16 Type: integer Modifiable: No Changes take place: At Creation	The number of logical partitions the databases is split into. We recommend keeping this value low. This value is set when you create the parameter group. When assigning a new parameter group to a cluster, this value must be the same in both the old and new parameter groups.
hash-max-ziplist-entries	Default: 512 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for hashes. Hashes with fewer than the specified number of entries are stored using a special encoding that saves space.
hash-max-ziplist-value	Default: 64 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for hashes. Hashes with entries that are smaller than the specified number of bytes are stored using a special encoding that saves space.
list-max-ziplist-entries	Default: 512 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for lists. Lists with fewer than the specified number of entries are stored using a special encoding that saves space.
list-max-ziplist-value	Default: 64 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for lists. Lists with entries that are smaller than the specified number of bytes are stored using a special encoding that saves space.
lua-time-limit	Default: 5000 Type: integer Modifiable: No	The maximum execution time for a Lua script, in milliseconds, before ElastiCache takes action to stop the script. If lua-time-limit is exceeded, all Redis commands will return an error of the form ____-BUSY. Since this state can cause interference with many essential Redis operations, ElastiCache will first issue a SCRIPT KILL command. If this is unsuccessful, ElastiCache will forcibly restart Redis.
maxclients This value applies to all instance types except those explicity specified	Default: 65000 Type: integer Modifiable: No	The maximum number of clients that can be connected at one time.
	t2.medium Default: 20000 Type: integer Modifiable: No
	t2.small Default: 20000 Type: integer Modifiable: No
	t2.micro Default: 20000 Type: integer Modifiable: No
	t4g.micro Default: 20000 Type: integer Modifiable: No
	t3.medium Default: 65000 Type: integer Modifiable: No
	t3.small Default: 65000 Type: integer Modifiable: No
	t3.micro Default: 20000 Type: integer Modifiable: No
maxmemory-policy	Default: volatile-lru Type: string Modifiable: Yes Changes Take Effect: Immediately	The eviction policy for keys when maximum memory usage is reached. Valid values are: volatile-lru | allkeys-lru | volatile-random | allkeys-random | volatile-ttl | noeviction For more information, see Using Redis as an LRU cache.
maxmemory-samples	Default: 3 Type: integer Modifiable: Yes Changes Take Effect: Immediately	For least-recently-used (LRU) and time-to-live (TTL) calculations, this parameter represents the sample size of keys to check. By default, Redis chooses 3 keys and uses the one that was used least recently.
reserved-memory	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The total memory, in bytes, reserved for non-data usage. By default, the Redis node will grow until it consumes the node's maxmemory (see Redis node-type specific parameters). If this occurs, then node performance will likely suffer due to excessive memory paging. By reserving memory you can set aside some of the available memory for non-Redis purposes to help reduce the amount of paging. This parameter is specific to ElastiCache, and is not part of the standard Redis distribution. For more information, see reserved-memory-percent and Managing Reserved Memory.
set-max-intset-entries	Default: 512 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for certain kinds of sets (strings that are integers in radix 10 in the range of 64 bit signed integers). Such sets with fewer than the specified number of entries are stored using a special encoding that saves space.
slave-allow-chaining	Default: no Type: string Modifiable: No	Determines whether a read replica in Redis can have read replicas of its own.
slowlog-log-slower-than	Default: 10000 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The maximum execution time, in microseconds, for commands to be logged by the Redis Slow Log feature.
slowlog-max-len	Default: 128 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The maximum length of the Redis Slow Log.
tcp-keepalive	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	If this is set to a nonzero value (N), node clients are polled every N seconds to ensure that they are still connected. With the default setting of 0, no such polling occurs. Important Some aspects of this parameter changed in Redis version 3.2.4. See Parameters changed in Redis 3.2.4 (enhanced).
timeout	Default: 0 Type: integer Modifiable: Yes Changes Take Effect: Immediately	The number of seconds a node waits before timing out. Values are: 0 – never disconnect an idle client. 1-19 – invalid values. >=20 – the number of seconds a node waits before disconnecting an idle client.
zset-max-ziplist-entries	Default: 128 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for sorted sets. Sorted sets with fewer than the specified number of elements are stored using a special encoding that saves space.
zset-max-ziplist-value	Default: 64 Type: integer Modifiable: Yes Changes Take Effect: Immediately	Determines the amount of memory used for sorted sets. Sorted sets with entries that are smaller than the specified number of bytes are stored using a special encoding that saves space.

Note

If you do not specify a parameter group for your Redis 2.6.13 cluster, then a default parameter group (default.redis2.6) will be used. You cannot change the values of any parameters in the default parameter group; however, you can always create a custom parameter group and assign it to your cluster at any time.

Redis node-type specific parameters

Although most parameters have a single value, some parameters have different values depending on the node type used. The following table shows the default values for the maxmemory, client-output-buffer-limit-slave-hard-limit, and client-output-buffer-limit-slave-soft-limit parameters for each node type. The value of maxmemory is the maximum number of bytes available to you for use, data and other uses, on the node. For more information, see Available memory.

Note

The maxmemory parameter cannot be modified.

Node type	Maxmemory	Client-output-buffer-limit-slave-hard-limit	Client-output-buffer-limit-slave-soft-limit
cache.t1.micro	142606336	14260633	14260633
cache.t2.micro	581959680	58195968	58195968
cache.t2.small	1665138688	166513868	166513868
cache.t2.medium	3461349376	346134937	346134937
cache.t3.micro	536870912	53687091	53687091
cache.t3.small	1471026299	147102629	147102629
cache.t3.medium	3317862236	331786223	331786223
cache.t4g.micro	536870912	53687091	53687091
cache.t4g.small	1471026299	147102629	147102629
cache.t4g.medium	3317862236	331786223	331786223
cache.m1.small	943718400	94371840	94371840
cache.m1.medium	3093299200	309329920	309329920
cache.m1.large	7025459200	702545920	702545920
cache.m1.xlarge	14889779200	1488977920	1488977920
cache.m2.xlarge	17091788800	1709178880	1709178880
cache.m2.2xlarge	35022438400	3502243840	3502243840
cache.m2.4xlarge	70883737600	7088373760	7088373760
cache.m3.medium	2988441600	309329920	309329920
cache.m3.large	6501171200	650117120	650117120
cache.m3.xlarge	14260633600	1426063360	1426063360
cache.m3.2xlarge	29989273600	2998927360	2998927360
cache.m4.large	6892593152	689259315	689259315
cache.m4.xlarge	15328501760	1532850176	1532850176
cache.m4.2xlarge	31889126359	3188912636	3188912636
cache.m4.4xlarge	65257290629	6525729063	6525729063
cache.m4.10xlarge	166047614239	16604761424	16604761424
cache.m5.large	6854542746	685454275	685454275
cache.m5.xlarge	13891921715	1389192172	1389192172
cache.m5.2xlarge	27966669210	2796666921	2796666921
cache.m5.4xlarge	56116178125	5611617812	5611617812
cache.m5.12xlarge	168715971994	16871597199	16871597199
cache.m5.24xlarge	337500562842	33750056284	33750056284
cache.m6g.large	6854542746	685454275	685454275
cache.m6g.xlarge	13891921715	1389192172	1389192172
cache.m6g.2xlarge	27966669210	2796666921	2796666921
cache.m6g.4xlarge	56116178125	5611617812	5611617812
cache.m6g.8xlarge	111325552312	11132555231	11132555231
cache.m6g.12xlarge	168715971994	16871597199	16871597199
cache.m6g.16xlarge	225000375228	22500037523	22500037523
cache.c1.xlarge	6501171200	650117120	650117120
cache.r3.large	14470348800	1468006400	1468006400
cache.r3.xlarge	30513561600	3040870400	3040870400
cache.r3.2xlarge	62495129600	6081740800	6081740800
cache.r3.4xlarge	126458265600	12268339200	12268339200
cache.r3.8xlarge	254384537600	24536678400	24536678400
cache.r4.large	13201781556	1320178155	1320178155
cache.r4.xlarge	26898228839	2689822883	2689822883
cache.r4.2xlarge	54197537997	5419753799	5419753799
cache.r4.4xlarge	108858546586	10885854658	10885854658
cache.r4.8xlarge	218255432090	21825543209	21825543209
cache.r4.16xlarge	437021573120	43702157312	43702157312
cache.r5.large	14037181030	1403718103	1403718103
cache.r5.xlarge	28261849702	2826184970	2826184970
cache.r5.2xlarge	56711183565	5671118356	5671118356
cache.r5.4xlarge	113609865216	11360986522	11360986522
cache.r5.12xlarge	341206346547	34120634655	34120634655
cache.r5.24xlarge	682485973811	68248597381	68248597381
cache.r6g.large	14037181030	1403718103	1403718103
cache.r6g.xlarge	28261849702	2826184970	2826184970
cache.r6g.2xlarge	56711183565	5671118356	5671118356
cache.r6g.4xlarge	113609865216	11360986522	11360986522
cache.r6g.8xlarge	225000375228	22500037523	22500037523
cache.r6g.12xlarge	341206346547	34120634655	34120634655
cache.r6g.16xlarge	450000750456	45000075046	45000075046
cache.r6gd.xlarge	28261849702	2826184970	2826184970
cache.r6gd.2xlarge	56711183565	5671118356	5671118356
cache.r6gd.4xlarge	113609865216	11360986522	11360986522
cache.r6gd.8xlarge	225000375228	22500037523	22500037523
cache.r6gd.12xlarge	341206346547	34120634655	34120634655
cache.r6gd.16xlarge	450000750456	45000075046	45000075046
cache.r7g.large	14037181030	1403718103	1403718103
cache.r7g.xlarge	28261849702	2826184970	2826184970
cache.r7g.2xlarge	56711183565	5671118356	5671118356
cache.r7g.4xlarge	113609865216	11360986522	11360986522
cache.r7g.8xlarge	225000375228	22500037523	22500037523
cache.r7g.12xlarge	341206346547	34120634655	34120634655
cache.r7g.16xlarge	450000750456	45000075046	45000075046
cache.m7g.large	6854542746	685454275	685454275
cache.m7g.xlarge	13891921715	1389192172	1389192172
cache.m7g.2xlarge	27966669210	2796666921	2796666921
cache.m7g.4xlarge	56116178125	5611617812	5611617812
cache.m7g.8xlarge	111325552312	11132555231	11132555231
cache.m7g.12xlarge	168715971994	16871597199	16871597199
cache.m7g.16xlarge	225000375228	22500037523	22500037523
cache.c7gn.large	3317862236	1403718103	1403718103
cache.c7gn.xlarge	6854542746	2826184970	2826184970
cache.c7gn.2xlarge	13891921715	5671118356	5671118356
cache.c7gn.4xlarge	27966669210	11360986522	11360986522
cache.c7gn.8xlarge	56116178125	22500037523	22500037523
cache.c7gn.12xlarge	84357985997	34120634655	34120634655
cache.c7gn.16xlarge	113609865216	45000075046	45000075046

Note

All current generation instance types are created in an Amazon Virtual Private Cloud VPC by default.

T1 instances do not support Multi-AZ.

T1 and T2 instances do not support Redis AOF.

Redis configuration variables appendonly and appendfsync are not supported on Redis version 2.8.22 and later.