This page provides a list of Memorystore for Memcached's modifiable and unmodifiable Memcached configuration parameters, as well as the default values for the parameters.
Modifiable configuration parameters
You can modify the following parameters when creating or updating a Memorystore for Memcached instance. Updating parameters requires you to change and apply parameters in two separate steps. For more information about how to change these configurations, see Configuring Memcached instances .
Parameter
Acceptable values
Default value
Description
listen-backlog (-b)
1-10000
1024
Adjustable length of the connection backlog queue. The backlog is the number
of network connection requests queued up to be processed by Memcached.
disable-flush-all (-F)
true, false
false
Setting
disable-flush-all
to true
disables the open
source Memcached flush-all
command. Modifying this configuration
increments the cmd_flush
counter, however a flush does not actually
occur.disable-watch (-W)
true, false
false
Memcached version 1.6.15, or later.If set to
true
this parameter disables the use of watch commands. Watchers allow you to connect to Memcached and inspect what's going on internally. Fetches, mutations, connection events etc. can be observed by using watch <fetchers|mutation|evictions|connevents|deletions>.max-item-size (-I)
524288-134217728 (bytes)
1048576
The Memcached parameter
max-item-size
sets the maximum size limit
for items stored in the instance. It is subject to a few additional constraints: -
max-item-sizemust be greater than or equal to slab_chunk_max.slab_chunk_max is set to 524288 bytes (512 KiB), and Memorystore for Memcached does not support changing this value. Therefore, the minimum value of max-item-size is 524288 bytes as opposed to the open source Memcached supported minimum (1024 bytes). -
max-item-sizemust be evenly divisible by slab_chunk_max (524288 bytes). -
max-item-sizemay not be more than half the total allocated size of the cache (the -m flag).
slab-min-size (-n)
1-1024 (bytes)
48
Sets the minimum item size and the size of the smallest Memcached slab.
slab-growth-factor (-f)
1.01-100.00
1.25
slab-growth-factor
is the multiplier used to calculate the size
of Memcached chunks/slabs. Lowering this value can improve the efficiency of
memory usage, but it depends on size of items to be stored and the available
memory of the instance.protocol (-B)
auto, ascii
auto
The binding protocol. Designates which protocol clients attempting to
connect to the server must use. Auto supports both binary and ascii protocol.
disable-cas (-C)
true, false
false
If
disable-cas
is set to true
, check and set (CAS)
operations are disabled. Disabling CAS operations uses 8 fewer bytes for each
item in the cache. Memcached uses the CAS operation to refresh an item's data if
it hasn't been updated since the last retrieval.disable-evictions (-M)
true, false
false
If set to
true
, when out of memory, Memcached returns an error
rather than evicting items. The instance won't accept writes until memory
becomes available.max-reqs-per-event (-R)
1-1000
20
Limits the number of requests per event that a single client connection can
make. After the client exceeds this value, the server prioritizes other clients
before it continues to process the original client request.
reserved-memory-percent
0.0-50.0
10.0
Sets your instance's Reserved Memory to the
specified percentage to increase the amount of space available for memory
overhead. This setting also reduces cache memory by the same percentage.
Instances created before October 25, 2021 have a default value of 0. For more
information, see Memory management best practices
.
Supported extended options
| Parameter | Acceptable values | Default value | Description |
|---|---|---|---|
|
track_sizes
|
true, false | false (disabled) | If track-sizes
is set to true
, users can run the
Memcached stats sizes
command. We do not recommend enabling this
configuration in production environments. |
|
watcher_logbuf_size
|
0-2097151 (kibibytes) | 262144 | The size of the write buffer per active watcher connected. Changing this
configuration adjusts the size of the watch
command's logging
buffer size. To avoid losing logs, increase watcher_logbuf_size
when it is full. |
|
worker_logbuf_size
|
48-524288 (kibibytes) | 65536 | Controls the size of the buffer for each active worker. The background thread reads from these buffers. |
|
lru_crawler
|
true, false | true (enabled) | The lru_crawler
configuration enables a background process that
scans through slabs and removes the least recently used (lru) items from those
slabs. This process is not CPU or memory intensive. Since it is enabled, the
process will run at launch time until you set lru_crawler
to false
. |
|
idle_timeout
|
0-86400 seconds | 0 (disabled) | Set to 0 (disabled) by default. This configurations sets time in seconds that clients can idle before timing out and disconnecting. |
|
lru_maintainer
|
true, false | true (enabled) | Enabled by default. lru_maintainer
is a background process that
determines how recently items are accessed in order to properly sort all items
by "least recently used" (lru). |
|
maxconns_fast
|
true, false | false (disabled) | Manages how Memcached processes new connections when the maximum number
of clients is reached. When maxconns-fast
is set to false
, connections exceeding the maximum connection limit are added
to a queue. When maxconns-fast
is set to true
,
connections exceeding the maximum connection limit are dropped and served an
error message. |
|
hash_algorithm
|
jenkins, murmur3, xxh3 | murmur3 | Designates the hash algorithm that the instance uses. Only instances using Memcached version 1.6.15 or higher can use the xxh3 config. |
Unmodifiable configuration parameters
The following table lists the Memcached configuration parameters that you cannot modify with Memorystore for Memcached, and the default values of the parameters. For more details, see the list of native Memcached configuration parameters .
| Parameter | Default value |
|---|---|
| port (-p) | 11211 |
| memory-limit (-m) | Memorystore sets this value to match the memory configured for each node in the instance node config. This configuration is unmodifiable; however, you can add Reserved Memory with the reserved memory configuration listed above. |
| threads (-t) | Memorystore sets this value to match the number of CPUs for each instance node. |
| conn-limit (-c) | 65000 per node |
| verbose (-v) | true |
| slab_automove | true (enabled) |
| slab_reassign | true (enabled) |
| enable-largepages (-L) | false (disabled) |
| lock-memory (-k) | false (disabled) |
| expirezero-does-not-evict | Not supported. Deprecated in Memcached 1.4.35. |
| slab_chunk_max | 524288 bytes |
| modern | true (enabled) |
What's next
- Learn how to configure Memcached instances .
- Monitor your Memcached instances .
