Showing posts from July, 2010

Core Dump Analysis with mdb/dbx

We had a Java application core dump. pstack and jstack will show all threads, but does not reveal which thread's guilty. Finding this one thread is simple:

# mdb /usr/bin/java /var/core/core_hostname_java_8081_8081_1276625241_1986 mdb: core file data for mapping at ffb80000 not saved: Bad address
Loading modules: [ ]
> $C
4d2fe5f8`_lwp_kill+8(6, 0, 20f04, ff36932c, ff38a000, ff38abdc)
4d2fe658`umem_do_abort+0x1c(3c, 4d2fe5a8, 6, 20e40, ff376ad8, 0)
4d2fe6b8`umem_err_recoverable+0x7c(ff377b54, a, 20d38, 656ebd84, ff38d0e8, ff377b5f)
4d2fe718`process_free+0x114(59c2008, 1, 0, 3e3a1000, 1ec08, 656d3e9c)
4d2fe778`XYZfree+0x1b8(59c2008, 65725b48, 15b, 4, 45a, 4d2fe9f8)
4d2fe810`XYZ_XYZ_FreeUser+0x28(59c2008, 4d2fea64, 4d2fe9e0, ffffff80, 80000000, 0)

Read/Write Performance Observations

As I mentioned in my previous post, we have now moved more active mailboxes to the Sun Oracle 7000 Storage System. Active means, incoming mails, POP3/IMAP4 accesses etc.


First we will take a look at disk read latency. We can see that more than 50% are lower than 10ms.

A sanity check on one of the NFS-clients confirms this

    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device      73.6   36.5  494.4  317.7  0.0  0.3    0.1    2.4   1  22 filer:/filesystemb     39.8   31.7  322.2  445.4  0.0  0.1    0.4    1.8   1  12 filer:/filesystemb

We can see that the average service time over this 10 second sample is around 2ms. Usually I'm not interpreting the %b value too much, other than if it constantly is at 100%. Newer file-systems read/write in bursts, which makes it not a good problem indicator.

Next we will take a look at the read I/Os. We can see a moderate number of read I/Os per disk.

We can also see the bandwith usage for this operation. For comparison I've m…

ARC Cache revisited

As we move more and more active mailboxes onto our OpenStorage box, it's time to have a look at the ARC cache.

If you remember, I already blogged a while ago about the ARC. At that time we had only inactive mailboxes, with almost no access other than incoming mails.

This is how it looks with active mailboxes:

I've colored all the hits. As you can see, there is a huge amount of metadata hits and prefetched metadata hits. You can also see some data hits and prefetched data hits.

We're now constantly adding more and more mailboxes to the system, resulting in more and more metadata. As the amount of data grows L2ARC will become more important. Stay tuned for a blog entry about how the L2ARC behaves...