Re: [libvirt] [PATCH] RFC: Remove all object hashtable caches from virConnectPtr

On Fri, Oct 29, 2010 at 12:52:18PM +0100, Daniel P. Berrange wrote: > The virConnectPtr struct will cache instances of all other > objects. APIs like virDomainLookupByUUID will return a > cached object, so if you do virDomainLookupByUUID twice in > a row, you'll get the same exact virDomainPtr instance. > > This does not have any performance benefit, since the actual > logic in virDomainLookupByUUID (and other APIs returning > virDomainPtr, etc instances) is not short-circuited. All > it does is to ensure there is only one single virDomainPtr > in existance for any given UUID. > > The caching has a number of downsides though, all relating > to stale data. If APIs aren't careful to always overwrite > the 'id' field in virDomainPtr it may become out of data. > Likewise for the name field, if a guest is renamed, or if > a guest is deleted, and then a new one created with the > same UUID but different name. > > This has been an ongoing, endless source of bugs for all > applications using libvirt from languages with garbage > collection, causing them to get virDomainPtr instances > from long ago with stale data. > > The caching is also a waste of memory resources, since > both applications, and language bindings often maintain > their own hashtable caches of object instances. > > This patch removes all the hash table caching, so all > APIs return brand new virDomainPtr (etc) object instances. No one has any comments on this change I thought would be hugely controversial... ?

From what you've decribed, it seems like a good change. I would have