[Opensim-dev] Memory cache
Alan M Webb
alan_webb at us.ibm.com
Thu May 21 19:10:52 UTC 2009
For an in-memory asset cache to be heavier than a network communication
with a remote is not amazing - it is incredible.
The first fetch would be expected to be marginally more expensive than a
direct reference to the server, but subsequent references should be orders
of magnitude better, even if the asset cache design were bad. For it to be
worse, it would need to be fundamentally broken.
What quantitative information do we have that demonstrates all of this?
The only outcome must be to fix the asset cache, if it is indeed broken.
If a virtual world has more than one client, then it must benefit from the
cache, provided the cache is still being used as the reference point for
asset fetching. There has been a lot of churn in the code of late, is it
possible that some of these changes have inadvertently disabled, or
bypassed, the cache?
Best regards
Alan
-------------------
T.J. Watson Research Center, Hawthorne, NY
1-914-784-7286
alan_webb at us.ibm.com
From:
diva at metaverseink.com
To:
opensim-dev at lists.berlios.de
Date:
05/21/2009 02:43 PM
Subject:
Re: [Opensim-dev] Memory cache
The cache, as configured, has 32K asset slots, which is a lot. So it
takes a while until the cache releases some objects for the GC to
collect. I think there's something else going on with that cache --
probably too many locking conflicts between threads, or something like
that. Whatever it is, it's much heavier than fetching the assets from
the remote asset server, which is amazing. And another amazing thing is
that remote fetching of so many assets at the same time (whenever a
client connects) has such good observable performance for the user.
If the purpose of the cache is to go easy on the asset server (not
necessarily improve the observable performance, which is already very
good without the mem cache) it might make more sense to use a file
system / local DB instead of a memory cache.
Stefan Andersson wrote:
> If the cache is releasing objects, I think we might well be seeing
> LOH fragmentation.
>
> http://msdn.microsoft.com/en-us/magazine/cc534993.aspx
>
> The solution would then be to break the binaries apart into byte cucks
> smaller than the LOH trshold.
>
> Best regards,
> Stefan Andersson
>
>
>
>
> > From: adam at deepthink.com.au
> > To: opensim-dev at lists.berlios.de
> > Date: Wed, 20 May 2009 17:21:51 -0400
> > Subject: Re: [Opensim-dev] Memory cache
> >
> > We are using an external caching library I believe, it could be
> sitting in there.
> >
> > Adam
> >
> > > -----Original Message-----
> > > From: opensim-dev-bounces at lists.berlios.de [mailto:opensim-dev-
> > > bounces at lists.berlios.de] On Behalf Of Melanie
> > > Sent: Wednesday, 20 May 2009 1:56 PM
> > > To: opensim-dev at lists.berlios.de
> > > Subject: Re: [Opensim-dev] Memory cache
> > >
> > > The surprise really is that the cache would be a performance loss
> > > instead of a performance gain. What is there that makes it so slow?
> > >
> > > Melanie
> > >
> > > Frisby, Adam wrote:
> > > > As chief engineer aboard the USS OSgrid, I might want to
recommend
> > > against this.
> > > >
> > > > Not having the sims cache assets will mean that every asset
request
> > > will hit the core asset server which in turn will result in higher
> > > bandwidth requirements for it in the long run. It doesn't appear to
> > > have made a huge impact on our bandwidth charts for this week yet -
> > > however I wouldn't be surprised if it did if everyone did this.
> > > >
> > > > Adam
> > > >
> > > > From: opensim-dev-bounces at lists.berlios.de [mailto:opensim-dev-
> > > bounces at lists.berlios.de] On Behalf Of Nebadon Izumi
> > > > Sent: Wednesday, 20 May 2009 10:19 AM
> > > > To: diva at metaverseink.com; opensim-dev at lists.berlios.de
> > > > Subject: Re: [Opensim-dev] Memory cache
> > > >
> > > > Yay for mistakes that end in gains!!! of course if anyone asks i
> > > planned this ;P anyway i thought people would like to see my ini
> > > changes.. this is what lead to the discovery:
> > > >
> > > > [OpenSim.ini]
> > > > ; The following is the configuration section for the new style
> > > grid servers
> > > > ; If you don't know what this is, don't enable it. It will eat
> > > your data,
> > > > ; format your hard drive and make all meat in your fridge spoil.
> > > > ; You have been warned.
> > > > ; Some of this is starting to work!
> > > > [Modules]
> > > > ; Choose one
> > > > ;AssetServices = "LocalAssetServicesConnector"
> > > > AssetServices = "RemoteAssetServicesConnector"
> > > > ;AssetServices = "HGAssetBroker"
> > > >
> > > > ; If you don't want asset caching in the regions, comment this
> > > > AssetCaching = "CoreAssetCache" ;<<<---*** SEE ERROR HERE ***---
> > > ->>>
> > > >
> > > > ; Choose one
> > > > ;UserServices = "LocalUserServicesConnector"
> > > > UserServices = "RemoteUserServicesConnector"
> > > >
> > > >
> > > > [AssetService]
> > > > ; Parameters for local assets, formerly known as "standalone"
> > > > LocalServiceModule =
> > > "OpenSim.Services.AssetService.dll:AssetService"
> > > > StorageProvider = "OpenSim.Data.SQLite.dll"
> > > > ;StorageProvider = "OpenSim.Data.MySQL.dll"
> > > > ;ConnectionString = "Data Source=localhost;Database=opensim;User
> > > ID=opensim;Password=opensim;"
> > > > DefaultAssetLoader =
> > > "OpenSim.Framework.AssetLoader.Filesystem.dll"
> > > > AssetLoaderArgs = "assets/AssetSets.xml"
> > > >
> > > > ; Parameters for remote assets, formerly known as "grid"
> > > > AssetServerURI = "http://assets.osgrid.org:8003/"
> > > >
> > > > ; Paremeters for the Hypergrid connector
> > > >
> > > > ;; Parameters for the HG Broker
> > > > ; Use this one if you have a standalone grid
> > > > ;LocalGridAssetService =
> > > "OpenSim.Services.AssetService.dll:AssetService"
> > > > ; Use this one if this sim is connected to a grid-wide asset
> > > server
> > > > ;LocalGridAssetService =
> > > "OpenSim.Services.Connectors.dll:AssetServiceConnector"
> > > > ;HypergridAssetService =
> > > "OpenSim.Services.AssetService.dll:HGAssetService"
> > > >
> > > > [AssetCache]
> > > > ; Number of buckets for assets
> > > > CacheBuckets = 32768
> > > >
> > > > [UserService]
> > > > ;LocalServiceModule =
> > > "OpenSim.Services.UserService.dll:UserService"
> > > >
> > > > [/OpenSim.ini]
> > > >
> > > > Please test this out and see if you see gains too and let us
know.
> > > >
> > > > Neb
> > > >
> > > >
> > > >
> > > >
---------------------------------------------------------------------
> > > ---
> > > >
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