[Deploying Sakai] Strange database connection memory issue at U-M

Sean DeMonner demonner at umich.edu
Thu Sep 17 06:48:20 PDT 2009


We're seeing some strange behavior on our app servers at U-M. Here  
are some details:

- Database connection memory usage on individual app servers  
increases by about .5 GB seemingly randomly every day or two. This is  
total memory for all 50 db pool connection from a given appserver,  
and confusingly enough there seems to be about an equal amount of  
increase in all 50 connections' memory usage

- The memory has not been released, except upon a restart. It is  
likely it is a cache that when filled up might evict some data, but  
we haven't filled it yet -- we've done preemptive restarts to avoid  
problems at the beginning of the term.

- Analysis of the log files does not reveal any telltale activities  
that might account for the increase in usage

- The behavior is new to 2.6 (was not observed in 2.5)

- We have seen it under light and heavy loads. What is interesting is  
that it is not strictly periodic nor obviously "random" (whatever  
that means)

- It looks like this (each color is an app server):

So far this doesn't seem like a crisis situation, but we are  
concerned that we have some strange resource gobbling activity that  
we can't explain.

Has anyone seem similar behavior or have any ideas about what might  
be causing the memory jumps?



Sean DeMonner, IT Senior Project Manager, CTools Implementation Group
Digital Media Commons @ The Duderstadt Center, U-M      (734) 615-9765
Pub Key 24DD6B09

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