Document caching
Three operations in the retrieval of a
document may take significant time:
At each stage, the server (in the first case) or browser (in
the other cases) may decide to keep a temporary copy of the
result. This copy should ideally be common to many browsers.
Automatic caching relieves the user of having to explicitly
save things which may be referred to again. It also relieves the
system of keeping multiple copies (one for each user who has read
the document). It allows local disk space to used optimally.
Cache management takes into account such factors as
-
expiry date
- file size
- time taken to get the file
- frequency of access
- time since access
As a guide to help a
cache program optimise the data it caches, it is useful if a
document is transmitted with an estimate by the server of the
lengt of time the data may be kept for. This allows fast changing
documents to be flushed from the system, preventing readers from
being mislead. (I would not propose any notification of document
changes to be distributed to cache managers automatically). For
example, an RFC may be cached for years, while the state of the
alarm system may be marked as valid for only one minute.
Window-oriented browsers effectively cache documents when they
keep several at a time in memory, in different windows. In this
case, for very volatile data, it may be useful to have the
browser automatically refresh the window when its data
expires.
( design issues
)_________________________________
Tim
BL