----- Original Message -----
> I am completely against this.
> It make the return value differ according to input which
> is a big no no when talking about type safe APIs.
> 
> The only reason we have this problem is because there is this
> thing against making multiple calls.
> 
> Just split it up.
> getVmRuntimeStats() - transient things like mem and cpu%
> getVmInformation() - (semi)static things like disk\networking layout
> etc.
> Each updated at different intervals.

+1 on splitting the data up into 2 separate API calls.
You could potentially add a checksum (md5, or any other way) of the "static" 
data to getVmRuntimeStats and not bother even with polling the VmInformation if 
this hasn't changed.  Then you could poll as often as you'd like the stats and 
immediately see if you also need to retrieve VmInfo or not (you rarely would).

> 
> ----- Original Message -----
> > From: "Vinzenz Feenstra" <vfeen...@redhat.com>
> > To: vdsm-devel@lists.fedorahosted.org, engine-de...@ovirt.org
> > Sent: Thursday, March 7, 2013 6:25:54 AM
> > Subject: [Engine-devel] Proposal VDSM <=> Engine Data Statistics
> > Retrieval   Optimization
> > 
> > 
> > Please find the prettier version on the wiki:
> > http://www.ovirt.org/Proposal_VDSM_-_Engine_Data_Statistics_Retrieval
> > 
> > Proposal VDSM - Engine Data Statistics Retrieval
> > VDSM <=> Engine data retrieval optimization
> > Motivation:
> > 
> > 
> > Currently the RHEVM engine is polling the a lot of data from VDSM
> > every 15 seconds. This should be optimized and the amount of data
> > requested should be more specific.
> > 
> > For each VM the data currently contains much more information than
> > actually needed which blows up the size of the XML content quite
> > big. We could optimize this by splitting the reply on the
> > getVmStats
> > based on the request of the engine into sections. For this reason
> > Omer Frenkel and me have split up the data into parts based on
> > their
> > usage.
> > 
> > This data can and usually does change during the lifetime of the
> > VM.
> > Rarely Changed:
> > 
> > 
> > This data is change not very frequent and it should be enough to
> > update this only once in a while. Most commonly this data changes
> > after changes made in the UI or after a migration of the VM to
> > another Host. Status = Running acpiEnable = true vmType = kvm
> > guestName = W864GUESTAGENTT displayType = qxl guestOs = Win 8
> > kvmEnable = true # this should be constant and never changed
> > pauseCode = NOERR monitorResponse = 0 session = Locked # unused
> > netIfaces = [{'name': 'Realtek RTL8139C+ Fast Ethernet NIC',
> > 'inet6':  ['fe80::490c:92bb:bbcc:9f87'], 'inet': ['10.34.60.148'],
> > 'hw': '00:1a:4a:22:3c:db'}] appsList = ['RHEV-Tools 3.2.4',
> > 'RHEV-Agent64 3.2.3', 'RHEV-Serial64 3.2.3', 'RHEV-Network64
> > 3.2.2',
> > 'RHEV-Network64 3.2.3', 'RHEV-Block64 3.2.3', 'RHEV-Balloon64
> > 3.2.3', 'RHEV-Balloon64 3.2.2', 'RHEV-Agent64 3.2.2', 'RHEV-USB
> > 3.2.3', 'RHEV-Block64 3.2.2', 'RHEV-Serial64 3.2.2'] pid = 11314
> > guestIPs = 10.34.60.148 # duplicated info displayIp = 0 displayPort
> > = 5902 displaySecurePort = 5903 username = user@W864GUESTAGENTT
> > clientIp = lastLogin = 1361976900.67 Often Changed:
> > 
> > 
> > This data is changed quite often however it is not necessary to
> > update this data every 15 seconds. As this is cumulative data and
> > reflects the current status, and it does not need to be snapshotted
> > every 15 seconds to retrieve statistics. The data can be retrieved
> > in much more generous time slices. (e.g. Every 5 minutes) network =
> > {'vnet1': {'macAddr': '00:1a:4a:22:3c:db', 'rxDropped': '0',
> > 'txDropped': '0', 'rxErrors': '0', 'txRate': '0.0', 'rxRate':
> > '0.0',
> > 'txErrors': '0', 'state': 'unknown', 'speed': '100', 'name':
> > 'vnet1'}} disksUsage = [{'path': 'c:\\', 'total': '64055406592',
> > 'fs': 'NTFS', 'used': '19223846912'}, {'path': 'd:\\', 'total':
> > '3490912256', 'fs': 'UDF', 'used': '3490912256'}] timeOffset =
> > 14422
> > elapsedTime = 68591 hash = 2335461227228498964 statsAge = 0.09 #
> > unused Often Changed but unused
> > 
> > 
> > This data does not seem to be used in the engine at all. It is not
> > even used in the data warehouse. memoryStats = {'swap_out': '0',
> > 'majflt': '0', 'mem_free': '1466884', 'swap_in': '0', 'pageflt':
> > '0', 'mem_total': '2096736', 'mem_unused': '1466884'} balloonInfo =
> > {'balloon_max': 2097152, 'balloon_cur': 2097152} disks = {'vda':
> > {'readLatency': '0', 'apparentsize': '64424509440', 'writeLatency':
> > '1754496',  'imageID': '28abb923-7b89-4638-84f8-1700f0b76482',
> > 'flushLatency': '156549',  'readRate': '0.00', 'truesize':
> > '18855059456', 'writeRate': '952.05'}, 'hdc': {'readLatency': '0',
> > 'apparentsize': '0', 'writeLatency': '0', 'flushLatency': '0',
> > 'readRate': '0.00', 'truesize': '0', 'writeRate': '0.00'}} Very
> > frequent uppdates needed by webadmin portal:
> > 
> > 
> > This data is mostly needed for the webadmin portal and might be
> > required to be updated quite often. An exception here is the
> > statsAge field, which seems to be unused by the Engine. This data
> > could be requested every 15 seconds to keep things as they are now.
> > cpuSys = 2.32 cpuUser = 1.34 memUsage = 30 Proposed Solution for
> > VDSM & Engine:
> > 
> > 
> > We will introduce new optional parameters to getVmStats,
> > getAllVmStats and list to allow a finer grained specification of
> > data which should be included.
> > 
> > Parameter: statsType = <string> (getVmStats, getAllVmStats only)
> > Allowed values:
> > 
> >     * full (default to keep backwards compatibility)
> >     * app-list (Just send the application list)
> >     * rare (include everything from rarely changed to very
> >     frequent)
> >     * often (include everything from often changed to very
> >     frequent)
> >     * frequent (only send the very frequently changed items)
> > 
> > 
> > 
> > Parameter: clientId = <string> The client id is specified by the
> > client and should be unique however constantly used.
> > 
> > Parameter: diff = <boolean> In combination with the clientId VDSM
> > will send only differences to the previous request from the named
> > clientId. (if diff=true)
> > 
> > 
> > Additional Change:
> > 
> > 
> > Besides the introduction of the new parameters for list, getVmStats
> > and getAllVmStats it might make sense to include a hash for the
> > appList into the rarely changed section of the response which would
> > allow to identify changes and avoid having to sent the complete
> > appList every so often and only if the hash known to the client is
> > outdated.
> > 
> > Note: The appList (Application List) reported by the guest agent
> > could be fully implemented on request only, as long as the guest
> > agent installed supports this. As there seems to be a request to
> > have the complete list of installed applications on all guests this
> > data could be quite extensive and a huge list. On the other hand
> > this data is only rarely visible and therefore it should not be
> > requested all the time and only on demand. Improvement of the Guest
> > Agent:
> > 
> > 
> > As part of the proposed solution it is necessary to improve the
> > guest
> > agent as well. For the full application list there should be
> > implemented a caching system which will be fully reactive and
> > should
> > not poll the application list for example all the time. The guest
> > can create a prepared data file containing all data in the JSON
> > format (as used for the communication with VDSM via VIO) and just
> > have to read that file from disk and directly sends it to VDSM.
> > However it is quite possible that this list is to big and it might
> > have to be chunked into pieces. (Multiple messages, which would
> > have
> > to be supported by VDSM then as well) The solution for this is to
> > make VDSM request this data and it will retrieve the data necessary
> > on request only. --
> > Regards,
> > 
> > Vinzenz Feenstra | Senior Software Engineer
> > RedHat Engineering Virtualization R & D
> > Phone: +420 532 294 625
> > IRC: vfeenstr or evilissimo
> > 
> > Better technology. Faster innovation. Powered by community
> > collaboration.
> > See how it works at redhat.com
> > _______________________________________________
> > Engine-devel mailing list
> > engine-de...@ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
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