Re: [Libvir] Scability / performance fix for virDomainLookupByID

On Fri, Jul 07, 2006 at 03:47:59PM +0100, Daniel P. Berrange wrote: > Attached is a patch to significantly increase scalability / performance of > the xenDaemonLookupByID method. The current implementation would get a > list of all domain names from XenD, and then iterate doing a HTTP GET on > /xend/domain/[name] until the domain with match ID was found. THis had > O(n) complexity, with the result that when running on a system with 20 > actives domains, 'virsh list' would have O(n^2) complexity needing ~230 > HTTP calls, giving a runtime of ~9 seconds. > > The patch is to make the code do a HTTP GET on /xend/domain/[id] which we > just discovered is a valid URL to access. This makes the method call O(1), I should have guessed that earlier, especially after the report last week about virDomainLookupByName(conn, "1") working fine ... > and 'virsh list' is now a saner O(n), and completes in ~1 second. While > still not great performance, this is certainly much better. I think it > ought to be possible to optimize the code still further so that XenD is > avoided altogether for simple commands which can be fullfilled purely > with data available from Hypervisor, but that will need further > investigation. > > Please review the patch in case I missed any bugs / edge cases just 2 small things: in xenDaemonLookupByID, it seems (but I may have misread the patch) that the free of name in the error code in case the rpc failed is a bit risky and should be guarded by if (name != NULL)

and the documentation for the new function in xend_internal.h is the old one inherited from Anthony first version, I somehow deprecated it, documenting the function itself in the .c file, but it's just nitpicking :-)