3.1 KiB
#Cache
Overview
The cache filter is capable of caching the result of SELECTs, so that subsequent identical SELECTs are served directly by MaxScale, without being routed to any server.
Configuration
The cache filter is straightforward to configure and simple to add to any existing service.
[Cache]
type=filter
module=cache
ttl=5
storage=...
storage_options=...
[Cached Routing Service]
type=service
...
filters=Cache
Each configured cache filter uses a storage of its own. That is, if there are two services, each configured with a specific cache filter, then, even if queries target the very same servers the cached data will not be shared.
Two services can use the same cache filter, but then either the services should use the very same servers or a completely different set of servers, where the used table names are different. Otherwise there can be unintended sharing.
Filter Parameters
The cache filter has one mandatory parameter - storage - and a few
optional ones.
storage
The name of the module that provides the storage for the cache. That
module will be loaded and provided with the value of storage_options as
argument. For instance:
storage=storage_rocksdb
storage_options
A comma separated list of arguments to be provided to the storage module,
specified in storage, when it is loaded. Note that the needed arguments
depend upon the specific module. For instance,
storage_options=storage_specific_option1=value1,storage_specific_option2=value2
allowed_references
Specifies whether any or only fully qualified references are allowed in queries stored to the cache.
allowed_references=[qualified|any]
The default is qualified, which means that only queries where
the database name is included in the table name are subject to caching.
select col from db.tbl;
If any is specified, then also queries where the table name is not
fully qualified are subject to caching.
select col from tbl;
Care should be excersized before this setting is changed, because, for instance, the following is likely to produce unexpected results.
use db1;
select col from tbl;
...
use db2;
select col from tbl;
The setting can be changed to any, provided fully qualified names
are always used or if the names of tables in different databases are
different.
max_resultset_rows
Specifies the maximum number of rows a resultset can have in order to be stored in the cache. A resultset larger than this, will not be stored.
max_resultset_rows=1000
Zero or a negative value is interpreted as no limitation.
The default value is -1.
max_resultset_size
Specifies the maximum size a resultset can have, measured in kibibytes, in order to be stored in the cache. A resultset larger than this, will not be stored.
max_resultset_size=128
The default value is 64.
ttl
Time to live; the amount of time - in seconds - the cached result is used before it is refreshed from the server.
If nothing is specified, the default ttl value is 10.
ttl=60
#Storage