Modifying Configuration Parameters

Procedure

1. Log in to the DCS console.
2. Click in the upper left corner and select a region and a project.
3. In the navigation pane, choose Cache Manager.
4. On the Cache Manager page, click the name of the DCS instance you want to configure.
5. Choose Instance Configuration > Parameters.
6. On the Parameters page, click Modify.
7. Modify parameters based on your requirements.

   Table 1 and Table 2 describe the parameters. In most cases, retain the default values.

   Table 1 DCS Redis instance configuration parameters

   Parameter	Description	Value Range	Default Value
   active-expire-num	Number of expired keys that can be deleted in regular scans. Redis 3.0 instances do not have this parameter.	1–1000	20
   timeout	The maximum amount of time (in seconds) a connection between a client and the DCS instance can be allowed to remain idle before the connection is terminated. A setting of 0 means that this function is disabled. Proxy Cluster instances do not have this parameter.	0–7200 seconds	0
   appendfsync	Controls how often fsync() transfers cached data to the disk. Note that some OSs will perform a complete data transfer but some others only make a "best-effort" attempt. There are three settings: no: fsync() is never called. The OS will flush data when it is ready. This mode offers the highest performance. always: fsync() is called after every write to the AOF. This mode is very slow, but also very safe. everysec: fsync() is called once per second. This mode provides a compromise between safety and performance. Single-node instances do not have this parameter.	no always everysec	no
   appendonly	Indicates whether to log each modification of the instance (that is, data persistence). By default, data is written to disks asynchronously in Redis. If this function is disabled, recently-generated data might be lost in the event of a power failure. Options: yes: enabled no: disabled Single-node instances do not have this parameter.	yes no	yes
   client-output-buffer-limit-slave-soft-seconds	Number of seconds that the output buffer remains above client-output-buffer-slave-soft-limit before the client is disconnected. Single-node instances do not have this parameter.	0–60	60
   client-output-buffer-slave-hard-limit	Hard limit (in bytes) on the output buffer of replica clients. Once the output buffer exceeds the hard limit, the client is immediately disconnected. Single-node instances do not have this parameter.	Depends on the instance type and specifications.	Depends on the instance type and specifications.
   client-output-buffer-slave-soft-limit	Soft limit (in bytes) on the output buffer of replica clients. Once the output buffer exceeds the soft limit and continuously remains above the limit for the time specified by the client-output-buffer-limit-slave-soft-seconds parameter, the client is disconnected. Single-node instances do not have this parameter.	Depends on the instance type and specifications.	Depends on the instance type and specifications.
   maxmemory-policy	The deletion policy to apply when the maxmemory limit is reached. Options: volatile-lru: Evict keys by trying to remove the less recently used (LRU) keys first, but only among keys that have an expire set. (Recommended) allkeys-lru: Evict keys by trying to remove the LRU keys first. volatile-random: evict keys randomly, but only evict keys with an expire set. allkeys-random: Evict keys randomly. volatile-ttl: Evict keys with an expire set, and try to evict keys with a shorter time to live (TTL) first. noeviction: Do not delete any keys and only return errors when the memory limit was reached. volatile-lfu: Evict keys by trying to remove the less frequently used (LFU) keys first, but only among keys that have an expire set. allkeys-lfu: Evict keys by trying to remove the LFU keys first.	Depends on the instance version.	Depends on the instance version and type.
   lua-time-limit	Maximum time allowed for executing a Lua script (in milliseconds).	100–5000	5,000
   master-read-only	Sets the instance to be read-only. All write operations will fail. Proxy Cluster instances do not have this parameter.	yes no	no
   maxclients	The maximum number of clients allowed to be concurrently connected to a DCS instance. Proxy Cluster instances do not have this parameter.	Depends on the instance type and specifications.	Depends on the instance type and specifications.
   proto-max-bulk-len	Maximum size of a single element request (in bytes).	1,048,576–536,870,912	536,870,912
   repl-backlog-size	The replication backlog size (bytes). The backlog is a buffer that accumulates replica data when replicas are disconnected from the master. When a replica reconnects, a partial synchronization is performed to synchronize the data that was missed while replicas were disconnected. Single-node instances do not have this parameter.	16,384–1,073,741,824	1,048,576
   repl-backlog-ttl	The amount of time, in seconds, before the backlog buffer is released, starting from the last a replica was disconnected. The value 0 indicates that the backlog is never released. Single-node instances do not have this parameter.	0–604,800	3,600
   repl-timeout	Replication timeout (in seconds). Single-node instances do not have this parameter.	30–3,600	60
   hash-max-ziplist-entries	Hashes are encoded using a memory efficient data structure when the number of entries in hashes is less than the value of this parameter.	1–10,000	512
   hash-max-ziplist-value	Hashes are encoded using a memory efficient data structure when the biggest entry in hashes does not exceed the length threshold indicated by this parameter.	1–10,000	64
   set-max-intset-entries	When a set is composed of just strings that happen to be integers in radix 10 in the range of 64 bit signed integers, sets are encoded using a memory efficient data structure.	1–10,000	512
   zset-max-ziplist-entries	Sorted sets are encoded using a memory efficient data structure when the number of entries in sorted sets is less than the value of this parameter.	1–10,000	128
   zset-max-ziplist-value	Sorted sets are encoded using a memory efficient data structure when the biggest entry in sorted sets does not exceed the length threshold indicated by this parameter.	1–10,000	64
   latency-monitor-threshold	Threshold time in latency monitoring. Unit: millisecond. Set to 0: Latency monitoring is disabled. Set to more than 0: All with at least this many milliseconds of latency will be logged. By running the LATENCY command, you can perform operations related to latency monitoring, such as obtaining statistical data, and configuring and enabling latency monitoring. Proxy Cluster instances do not have this parameter.	0–86,400,000 ms	0
   notify-keyspace-events	Controls which keyspace events notifications are enabled for. If the value is an empty string, this function is disabled. A combination of different values can be used to enable notifications for multiple event types. Possible values: K: Keyspace events, published with the __keyspace@__ prefix. E: Keyevent events, published with __keyevent@__ prefix g: Generic commands (non-type specific) such as DEL, EXPIRE, and RENAME $: String commands l: List commands s: Set commands h: Hash commands z: Sorted set commands x: Expired events (events generated every time a key expires) e: Evicted events (events generated when a key is evicted for maxmemory) A: an alias for "g$lshzxe" The parameter value must contain either K or E. A cannot be used together with any of the characters in "g$lshzxe". For example, the value Kl means that Redis will notify Pub/Sub clients about keyspace events and list commands. The value AKE means Redis will notify Pub/Sub clients about all events. Proxy Cluster instances do not have this parameter.	See the parameter description.	Ex
   slowlog-log-slower-than	Redis records queries that exceed a specified execution time. slowlog-log-slower-than is the maximum time allowed, in microseconds, for command execution. If this threshold is exceeded, Redis will record the query.	0–1,000,000	10,000
   slowlog-max-len	The maximum allowed number of slow queries that can be logged. Slow query log consumes memory, but you can reclaim this memory by running the SLOWLOG RESET command.	0–1000	128

   

   1. For more information about the parameters described in Table 1, visit https://redis.io/topics/memory-optimization.
   2. The latency-monitor-threshold parameter is usually used for fault location. After locating faults based on the latency information collected, change the value of latency-monitor-threshold to 0 to avoid unnecessary latency.
   3. More about the notify-keyspace-events parameter:
      • The parameter setting must contain at least a K or E.
      • A is an alias for "g$lshzxe" and cannot be used together with any of the characters in "g$lshzxe".
      • For example, the value Kl means that Redis will notify Pub/Sub clients about keyspace events and list commands. The value AKE means Redis will notify Pub/Sub clients about all events.
   4. Configurable parameters and their values vary depending on the instance type.

   Table 2 DCS Memcached instance configuration parameters

   Parameter	Description	Value Range	Default Value
   timeout	The maximum amount of time (in seconds) a connection between a client and the DCS instance can be allowed to remain idle before the connection is terminated. A setting of 0 means that this function is disabled.	0–7200 seconds	0
   maxclients	The maximum number of clients allowed to be concurrently connected to a DCS instance.	1000–10,000	10,000
   maxmemory-policy	The policy applied when the maxmemory limit is reached. For more information about data eviction, see What Is the Default Data Eviction Policy? or visit the Redis official website.	volatile-lru allkeys-lru volatile-random allkeys-random volatile-ttl noeviction	noeviction
   reserved-memory-percent	Percentage of the maximum available memory reserved for background processes, such as data persistence and replication.	0–80	30

8. After you have finished setting the parameters, click Save.
9. Click Yes to confirm the modification.

Typical Scenarios of Configuring Parameters

The following describes how to change the value of the appendonly parameter:

• If Redis is used as the cache and services are insensitive to Redis data losses, disable instance persistence to improve performance. In this case, change the value of appendonly to no. For details, see Procedure.
• If Redis is used as the database or services are sensitive to Redis data losses, enable instance persistence. In this case, change the value of appendonly to yes. For details, see Procedure. After instance persistence is enabled, you need to consider the frequency of writing Redis cache data to disks and the impact on the Redis performance. You can use this parameter together with the appendfsync parameter. There are three modes of calling fsync():
  • no: fsync() is never called. The OS will flush data when it is ready. This mode offers the highest performance.
  • always: fsync() is called after every write to the AOF. This mode is very slow, but also very safe.
  • everysec: fsync() is called once per second, ensuring both data security and performance.

Currently, the appendonly and appendfsync parameters can be modified on the console only for master/standby and Redis 4.0 and later Redis Cluster instances.