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Update cache documentation

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Johan Wikman 2017-01-20 13:30:58 +02:00
parent 872bbd1ab3
commit d012f137c6
1 changed files with 28 additions and 10 deletions
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Documentation/Filters/Cache.md
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@ -1,13 +1,25 @@
# 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.
The cache filter is a simple cache that is capable of caching the result of
SELECTs, so that subsequent identical SELECTs are served directly by MaxScale,
without the queries being routed to any server.
_Note that the cache is still experimental._
## Limitations
* Currently there is **no** cache invalidation, apart from _time-to-live_. This
will be changed in forthcoming releases.
* Resultsets of prepared statements are **not** cached. This will be changed
in forthcoming releases.
## Configuration
The cache filter is straightforward to configure and simple to add to any
existing service.
The cache is simple to add to any existing service. However, some experimentation
may be required in order to find the configuration settings that provide
the maximum benefit.
```
[Cache]
@ -18,7 +30,7 @@ soft_ttl=20
storage=...
storage_options=...
rules=...
debug=...
...
[Cached Routing Service]
type=service
@ -40,7 +52,9 @@ sharing.
### Filter Parameters
The cache filter has one mandatory parameter - `storage` - and a few
optional ones.
optional ones. Note that it is advisable to specify `max_size` to prevent
the cache from using up all memory there is, in case there is very litte
overlap among the queries.
#### `storage`
@ -48,7 +62,7 @@ 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=storage_inmemory
```
#### `storage_options`
@ -113,7 +127,9 @@ The maximum number of items the cache may contain. If the limit has been
reached and a new item should be stored, then an older item will be evicted.
Note that if `cached_data` is `thread_specific` then this limit will be
applied to each cache _separately_.
applied to each cache _separately_. That is, if a thread specific cache
is used, then the total number of cached items is #threads * the value
of `max_count`.
```
max_count=1000
```
@ -129,7 +145,8 @@ Note that the value of `max_size` must be at least as large as the value of
`max_resultset_size`.
Note that if `cached_data` is `thread_specific` then this limit will be
applied to each cache _separately_.
applied to each cache _separately_. That is, if a thread specific cache
is used, then the total size is #threads * the value of `max_size`.
```
max_size=1000
```
@ -175,7 +192,7 @@ denoting different logging.
* ` 2` (`0b00010`) A non-matching rule is logged.
* ` 4` (`0b00100`) A decision to use data from the cache is logged.
* ` 8` (`0b01000`) A decision not to use data from the cache is logged.
* '16' (`0b10000`) Higher level decisions are logged.
* `16` (`0b10000`) Higher level decisions are logged.
Default is `0`. To log everything, give `debug` a value of `31`.
@ -409,6 +426,7 @@ For instance, the following are equivalent:
"op": "like",
"value": "bob@.*"
}
```
Note that if _op_ is `=` or `!=` then the usual assumptions apply,
that is, a value of `bob` is equivalent with `'bob'@'%'`. If _like_