[libvirt] [PATCH v2] lib: Add note that bulk stats API queries may overrun RPC buffers

[Peter Krempa]

On Tue, May 23, 2017 at 17:19:53 +0200, Martin Kletzander wrote:
> On Tue, May 23, 2017 at 05:07:40PM +0200, Michal Privoznik wrote:
> > On 05/23/2017 04:35 PM, Martin Kletzander wrote:
> > > On Tue, May 23, 2017 at 04:23:30PM +0200, Peter Krempa wrote:

[...]

> > > > + * Note that this API is prone to exceeding maximum RPC if querying
> > > > too many VMs
> > > > + * with lots of statistics. It's suggested to query in batches of
> > > > 10VMs, which
> > > > + * should be good enough for VMs with 3000 disks + networks.
> > > > + *
> > > 
> > > Coming to think about it... Why don't we just batch this ourselves under
> > > the hood and just return the merged result?
> > 
> > Because:
> > 
> > https://www.redhat.com/archives/libvir-list/2017-May/msg00088.html
> > 
> 
> Not on the RPC level, the API would just be syntax sugar to
> virDomainListGetStats() if a flag was passed
> (e.g. VIR_DOMAIN_GET_ALL_STATS_I_DONT_REALLY_CARE_IF_THIS_IS_DONE_IN_ONE_LIBVIRT_CALL)

Also compared to a full fragmentation of the returned data, this would
result into a worst-case-scenario memory usage of MAX_SIZE *
NVMS_QUERIED_IN_ORIGINAL_CALL, when compared to an unbounded memory use
of the full fragmentation approach.
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