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

[Michal Privoznik]

On 05/23/2017 04:35 PM, Martin Kletzander wrote:
> On Tue, May 23, 2017 at 04:23:30PM +0200, Peter Krempa wrote:
>> Hint that the users should limit the number of VMs queried in the bulk
>> stats API.
>> ---
>> v2:
>> - added a suggestion of the number of queried VMs (valid after bump to
>> 32M message)
>>
>> src/libvirt-domain.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
>> index 310b91b37..aef061943 100644
>> --- a/src/libvirt-domain.c
>> +++ b/src/libvirt-domain.c
>> @@ -11315,6 +11315,10 @@ virConnectGetDomainCapabilities(virConnectPtr
>> conn,
>>  * VIR_CONNECT_GET_ALL_DOMAINS_STATS_SHUTOFF and/or
>>  * VIR_CONNECT_GET_ALL_DOMAINS_STATS_OTHER for all other states.
>>  *
>> + * Note that this API is prone to exceeding maximum RPC message size
>> on hosts
>> + * with lots of VMs so it's suggested to use virDomainListGetStats
>> with a
>> + * reasonable list of VMs as the argument.
>> + *
>>  * Returns the count of returned statistics structures on success, -1
>> on error.
>>  * The requested data are returned in the @retStats parameter. The
>> returned
>>  * array should be freed by the caller. See virDomainStatsRecordListFree.
>> @@ -11386,6 +11390,10 @@ virConnectGetAllDomainStats(virConnectPtr conn,
>>  * Note that any of the domain list filtering flags in @flags may be
>> rejected
>>  * by this function.
>>  *
>> + * 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

Michal