Multi-tenant Java 8 VM in beta

http://www.ibm.com/developerworks/java/library/j-multitenant-java/index.html

by SanderMak • 13 years ago

46 29 13 years ago

polskibus2• 13 years ago

Does anyone know if .NET runtime is multitenant? Would be great to know about the alternatives (and their future plans).

kevingadd• 13 years ago

.NET has a feature called 'application domains' which provides stuff pretty similar to this, but I don't know if the support is as complete. They use it for security sandboxing, on-demand code loading/unloading, etc.

http://msdn.microsoft.com/en-us/library/2bh4z9hs.aspx

rektide3• 13 years ago

I believe in Mono if one does Ahead-of-Time compilation the bytecode is just mem mapped in and can be shared between runtimes, giving you much of the advantage of this work.

pjmlp• 13 years ago

There is no bytecode any longer when you do AOT, just plain pure native code.

SideburnsOfDoom• 13 years ago

.Net runs in various places. Under IIS, you're thinking of Application Pools http://stackoverflow.com/questions/3868612/what-is-an-iis-ap...

polskibus2• 13 years ago

an app pool usually (without farm setting) translates to one w3wp process, so the deduplication doesn't take place. That would mean there's no real multitenancy in IIS via app pools.

silverlake• 13 years ago

Yes, .NET has had Application Domains since the beginning. It can be used for exactly this purpose.

"You can run several application domains in a single process with the same level of isolation that would exist in separate processes, but without incurring the additional overhead of making cross-process calls or switching between processes. The ability to run multiple applications within a single process dramatically increases server scalability."

http://msdn.microsoft.com/en-us/library/2bh4z9hs.aspx

rektide3• 13 years ago

Java has had Class Data Sharing (CDS) since jdk1.5, an archive of "standard libraries" shared between all instances. It can be rebuilt with additional libraries, speeding their load and reducing their footprint.

Links to notes on this, https://plus.google.com/113218107235105855584/posts/K9seVudj... . Stack overflow q, http://stackoverflow.com/questions/4692076/speed-up-applicat...

CDS is fantastically un-isolated and using it is going to be systemwide. You're still running many many java copies, and that is fat in size, ugly and busted in form. Containers like Tomcat exist to solve a near-like problem of being a many-application serving system. This virtualized virtual machine is definitely the first runtime that's oriented to multi-tenant, but if you look around, you can find some it's technical roots here and there.

modsrm• 13 years ago

Not sure it is the first one: http://www.waratek.com/product/cloudvm

eliasmacpherson• 13 years ago

I came across CDS before when trying to get desktop java applications to start up faster.

I also had hoped it would allow e.g. a constantly running fat server to run eclipse for multiple users more efficiently than each desktop duplicating work.

http://lukas.zapletalovi.com/2012/11/want-faster-java-startu...

I had thought CDS was just for Sun and IBM implementations, but from the above I can infer it works on OpenJDK too.

When you say, 'running many many java copies', do you mean java.exe?

6ren2• 13 years ago

Fantastic for sharing, though the startup time improvement is minor (e.g. I saw 17% improvement). BTW: that SO comment references a pdf that shows how to include your own classes, on pages 61-62 http://www.oracle.com/technetwork/jp/ondemand/java/20110519-...; tools link: http://hg.openjdk.java.net/jdk6/jdk6/jdk/file/tip/make/tools...

IBM's multi-tenancy gives 3.3 speedup, for HelloWorld - worse for others (maybe if they combined it with CDS?)

BTW: The only way to get instant Java startup is not to startup - use an already running JVM, with the classes already loaded. It's fast. Just leave it in the background til you need it - it's effectively a server. Especially good to invoke javac this way, for lightening compiles (if like me you don't use an IDE).

greyboy• 13 years ago

Interesting about keeping a JVM running for compilation. I'm curious about doing just this for my day job but can't seem to find a good explanation. Do you have any resources to point me to?

rektide3• 13 years ago

If one needs to be launching only a fixed set of programs fast, perhaps give CRIU, checkpoint restore in userspace, a try? Give the program time to warm up and load, checkpoint it, then restore a copy: run an already copy, rather than repeat the startup afresh. Post on CRIU from the same day: https://plus.google.com/113218107235105855584/posts/CNkhcV43...

trailfox• 13 years ago

Didn't Sun have an experimental MVM about 10 years ago?

raverbashing3• 13 years ago

Question: I had the impression that when you had several threads on a Java app this would result in several VMs, is this currently so, was so or it's my mistake and it was never like that?

SanderMak• 13 years ago

It was never like that. Threads have their own stack, but that's about it. They can access anything anywhere. Hence the current focus on concurrency using immutable message passing mechanisms on the JVM (actors etc.)

raverbashing3• 13 years ago

Or, to be more specific, what are the differences between thread handling under Linux and Windows regarding to the JVM?

Threads in Linux (in general) are separate process that share memory space, in Windows it's different and they're "threads" being scheduled under a parent process.

mhaymo• 13 years ago

The main cost of using the multitenant JVM is that tenants are less isolated than multiple applications that run in separate JVMs. For example, a native crash in the multitenant JVM affects all tenants.

Does anyone know what exactly is meant by a "native crash"?

frio• 13 years ago

If the JVM crashes.

njs12345• 13 years ago

For example, if a bug in the JVM or an external library causes a dereference of a (C/C++) null pointer.

ramblerman• 13 years ago

One permgen to kill them all

axelf• 13 years ago

I think java 8 gets rid of permgen

chii• 13 years ago

only to replace it with off heap memory iirc. Not sure what the benefit was tbh.

Multi-tenant Java 8 VM in beta

Related Stories