Clustering Manager Error

Dear All,

I tried to use 2 server with clustering plugin. Everythings works fine, my active user is about 18,000. But sometimes when I see on clustering menu one of my node become Not Available. And i got this error message in my error.log :

21:31:35 [org.jivesoftware.database.SequenceManager.getNextBlock(SequenceManager.java:24 0)] WARNING: failed to obtain next ID block due to thread contention. Trying again…

Can everybody give me why it’s happen and what is the solution for this?

Thanks

Agus