An R6 class for managing a persistent file-based cache
Cache provides an R6 API for managing an on-disk key-value
store for R objects. The objects are serialized to a single folder as
.rds files and the key of the object equals the name of the file.
Cache supports automatic removal of old files if the cache folder exceeds a
predetermined number of files, total size, or if the individual files exceed
a certain age.
rotor::DirectoryQueue -> Cache
dira character scalar. path of the directory in which to store the cache files
ninteger scalar: number of files in the cache
max_filessee the compress argument of base::saveRDS().
Note: this differs from the $compress argument of rotate().
max_filesinteger scalar: maximum number of files to keep in
the cache
dira character scalar. path of the directory in which to store the cache files
ninteger scalar: number of files in the cache
max_filessee the compress argument of base::saveRDS().
Note: this differs from the $compress argument of rotate().
max_filesinteger scalar: maximum number of files to keep in
the cache
max_sizescalar integer, character or Inf. Delete
cached files (starting with the oldest) until the total size of the
cache is below max_size. Integers are interpreted as bytes. You
can pass character vectors that contain a file size suffix like 1k
(kilobytes), 3M (megabytes), 4G (gigabytes), 5T (terabytes). Instead
of these short forms you can also be explicit and use the IEC suffixes
KiB, MiB, GiB, TiB. In Both cases 1 kilobyte is 1024 bytes, 1
megabyte is 1024 kilobytes, etc... .
max_age a Date scalar: Remove all backups before this date
a character scalar representing a Date in ISO format (e.g. "2019-12-31")
a character scalar representing an Interval in the form "<number> <interval>" (see rotate())
hashfunNULL or a function to generate a unique hash from the
object to be cached (see example). The hash must be a text string
that is a valid filename on the target system. If $hashfun is NULL,
a storage key must be supplied manually in cache$push(). If a new
object is added with the same key as an existing object, the existing
object will be overwritten without warning.
All cached files
new()
Cache$new( dir = dirname(file), max_files = Inf, max_size = Inf, max_age = Inf, compression = TRUE, hashfun = digest::digest, create_dir = TRUE )
create_dirlogical scalar. If TRUE dir is created if it
does not exist.
td <- file.path(tempdir(), "cache-test")
# When using a real hash function as hashfun, identical objects will only
# be added to the cache once
cache_hash <- Cache$new(td, hashfun = digest::digest)
cache_hash$push(iris)
cache_hash$push(iris)
cache_hash$files
cache_hash$purge()
# To override this behaviour use a generator for unique ids, such as uuid
if (requireNamespace("uuid")){
cache_uid <- Cache$new(td, hashfun = function(x) uuid::UUIDgenerate())
cache_uid$push(iris)
cache_uid$push(iris)
cache_uid$files
cache_uid$purge()
}
unlink(td, recursive = TRUE)
push()
push a new object to the cache
Cache$push(x, key = self$hashfun(x))
xany R object
keya character scalar. Key under which to store the cached
object. Must be a valid filename. Defaults to being generated by
$hashfun() but may also be supplied manually.
a character scalar: the key of the newly added object
read()
read a cached file
Cache$read(key)
keycharacter scalar. key of the cached file to read.
remove()
remove a single file from the cache
Cache$remove(key)
keycharacter scalar. key of the cached file to remove
pop()
Read and remove a single file from the cache
Cache$pop(key)
keycharacter scalar. key of the cached file to read/remove
prune()
Prune the cache
Delete cached objects that match certain criteria. max_files and
max_size deletes the oldest cached objects first; however, this is
dependent on accuracy of the file modification timestamps on your system.
For example, ext3 only supports second-accuracy, and some windows
version only support timestamps at a resolution of two seconds.
If two files have the same timestamp, they are deleted in the lexical
sort order of their key. This means that by using a function that
generates lexically sortable keys as hashfun (such as
ulid::generate()) you can enforce the correct deletion order. There
is no such workaround if you use a real hash function.
Cache$prune( max_files = self$max_files, max_size = self$max_size, max_age = self$max_age, now = Sys.time() )
max_files, max_size, max_agesee section Active Bindings.
nowa POSIXct datetime scalar. The current time (for max_age)
purge()
purge the cache (remove all cached files)
Cache$purge()
destroy()
purge the cache (remove all cached files)
Cache$destroy()
print()
Cache$print()
set_max_files()
Cache$set_max_files(x)
set_max_age()
Cache$set_max_age(x)
set_max_size()
Cache$set_max_size(x)
set_compression()
Cache$set_compression(x)
set_hashfun()
Cache$set_hashfun(x)
Other R6 Classes:
BackupQueueDateTime,
BackupQueueDate,
BackupQueueIndex,
BackupQueue,
DirectoryQueue
## ------------------------------------------------
## Method `Cache$new`
## ------------------------------------------------
td <- file.path(tempdir(), "cache-test")
# When using a real hash function as hashfun, identical objects will only
# be added to the cache once
cache_hash <- Cache$new(td, hashfun = digest::digest)
cache_hash$push(iris)
cache_hash$push(iris)
cache_hash$files
cache_hash$purge()
# To override this behaviour use a generator for unique ids, such as uuid
if (requireNamespace("uuid")){
cache_uid <- Cache$new(td, hashfun = function(x) uuid::UUIDgenerate())
cache_uid$push(iris)
cache_uid$push(iris)
cache_uid$files
cache_uid$purge()
}
unlink(td, recursive = TRUE)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.