[OPEN-ILS-DEV] caching and High Availability

[dkyle]

a short while ago, in a not too distant thread....

miker wrote this:
Once in a while a bug would pop up that would take a single machine
down.  That's no problem at all for the application proper; OpenSRF
just ignores the misbehaving machine and distributes the load to the
rest (yay opensrf).  However, it was a problem for memcache.  1/20th
of the session keys (and the search cache, and some other stuff) would
go away

I got off on a tangent looking at memory cache redundancy, but it 
suddenly occurred to me to ask:

Shouldn't the application take into account cache failure and gracefully 
adjust?

Why are critical things like session keys not written to disk during 
CachePut calls? and that disk store accessed if a Get call to memcache 
fails?

Isn't that the typical way memcache is used?

Although memcache distributes objects across machines/instances, any 
particular object is cached on only one machine, so there is always a 
possible single point of failure despite setting up a HA Cluster.


... or am I missing something?

Doug.