Hi,
I don't know if this is a feature already - but is it possible to "pause"
memcache's expiry?
For example we cache a lot of data in memcached (sourced from MySQL) that
is read only. If the underlying code knows the MySQL server has failed it
would be handy to "signal" memcached, and for memcached then to stop
expiring objects.
When you signal memcached to start expiring again it should re-evaluates
objects expiry date, and set it to be "now" + whatever the expiry time was,
perhaps minus how long the object had left to live before the system was
'paused'.
So if you pushed an object into cache with a 5 minute expiry time, and then
signalled to memcache to "pause" expiry in 3 minutes time - that object
would not expire - instead, when you signal memcached "begin expiry" it
would have it's expiry time at that point set to "now + 5 minutes - 3
minutes" = so now + 2 minutes.
The reasoning behind this is:
- In a failed MySQL environment our front line code can survive using
cached objects for a very long time if it has to, but we don't want them to
expire if we know MySQL has gone away (at the same time we don't want to
set object expiry times of hours unless we have to).
- We also don't want memcached to throw all the objects out the moment we
tell it to start expiring data again (to avoid the stampeding hurd).
Is this possibel with current memcached?
Maybe adding such a "pause" feature would be a good idea - you could have a
literal "pause" which mean no expired objects will be released from cache
(memory permitting) - but may all expire at once when the unpaused, and an
"adaptive pause" which means no expired objects would be released, and
their expiry time [upon pause removal] will be reevaluated in accordance
with the suggestion above.
Jon.
