-Re: Zookeeper session timeouts during RAID Checks
Patrick Hunt 2013-10-08, 06:53
Hi Srikanth. Do you see any of these in your server logs?
LOG.warn("fsync-ing the write ahead log in "
+ " took " + syncElapsedMS
+ "ms which will adversely effect
operation latency. "
+ "See the ZooKeeper troubleshooting guide");
On Mon, Oct 7, 2013 at 11:45 PM, Srikanth R <[EMAIL PROTECTED]> wrote:
> hi zookeepers,
> I am using zookeeper 3.4.5 in a 3 server ensemble mode. And its datadir is
> in a dedicated 6 disk 2.5TB Raid10 Volume. Only HDFS namenode/journal txns
> and Zookeeper txnlog/snapshots are written to this volume. The issue is
> whenever the weekly raid check is running, clients that have 5 Sec Timeouts
> are timing out randomly. Has anyone seen issues like this with datadir on
> Raid before ?
> Also there isnt much writes going into ZK, only hadoop-ha and hbase master
> are using the ZK services.
> 1. There are no cpu bottlenecks or memory/swapping issues on the boxes.
> 2. In ZK strace output, there are a few random 2-3 secs intervals where no
> system calls are recorded, which is weird. And most of the timeouts
> correspond to this time period. But not able to figure out what ZK does
> during that intervals.
> 3. Enabled GC logs, no traces of full GC during timeouts. Though there were
> full GCs recorded over period of time, the pause is only for 0.3-0.4 secs.
> Also tried the ConcMarkSweep GC without any improvement.
> 4. There are not network errors/timeouts.
> 5. At times I see a max latency of 3-4 secs in connection stats, but avg
> and min latency are 0.
> 6. ran zk-latencies.py and latency seems to be same with and without raid
> Here's the zookeeper config
> -bash-4.1$ df -h
> Filesystem Size Used Avail Use% Mounted on
> /dev/md2 116G 79G 32G 72% /
> tmpfs 12G 0 12G 0% /dev/shm
> /dev/md0 97M 31M 61M 34% /boot
> /dev/md3 2.6T 297M 2.5T 1% /data
> -bash-4.1$ cat /proc/mdstat
> Personalities : [raid10] [raid1]
> md3 : active raid10 sdc5 sdd5 sda5 sdf5 sdb5 sde5
> 2782511616 blocks super 1.1 512K chunks 2 near-copies [6/6] [UUUUUU]
> [===================>.] check = 95.3% (2654099584/2782511616)
> finish=41.5min speed=51516K/sec
> bitmap: 0/21 pages [0KB], 65536KB chunk
> Here are my queries,
> 1. what is the best way to find out what the Zookeeper threads are doing
> (strace hasnt helped much)
> 2. There isnt much data written to/read from ZK. why would ZK fail ?
> 3. Is it possible to trace all the requests that come in to ZK ?
> Please let me know if you need more info. Any help is greatly appreciated.