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

[Martin Kletzander]

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?

>  * 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.
>--
>2.12.2
>
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