Morning all. Day 2 begins... I discussed this with someone else earlier and they pointed out that we also have task trackers running on all of those nodes, which will affect the amount of memory being used when jobs are being run. Each tasktracker had a maximum of 8 maps and 8 reduces configured per node, with a JVM Xmx of 512mb each. Clearly this implies a fully utilised node will use 8*512mb + 8*512mb = 8GB of memory on tasks alone. That's before the datanode does anything, or HBase for that matter.
As such, I've dropped it to 4 maps, 4 reduces per node and reduced the Xmx to 256mb, giving a potential maximum task overhead of 2GB per node. Running 'vmstat 20' now, under load from mapreduce jobs, suggests that the actual free memory is about the same, but the memory cache is much much bigger, which presumably is healthlier as, in theory, that ought to relinquish memory to processes that request it. Lets see if that does the trick! ta Jamie On 7 July 2010 19:30, Jean-Daniel Cryans <[email protected]> wrote: > YouAreDead means that the region server's session was expired, GC > seems like your major problem. (file problems can happen after a GC > sleep because they were moved around while the process was sleeping, > you also get the same kind of messages with xcievers issue... sorry > for the confusion) > > By over committing the memory I meant trying to fit too much stuff in > the amount of RAM that you have. I guess it's the map and reduce tasks > that eat all the free space? Why not lower their number? > > J-D > > On Wed, Jul 7, 2010 at 11:22 AM, Jamie Cockrill > <[email protected]> wrote: >> PS, I've now reset my MAX_FILESIZE back to the default. (from the 1GB >> i raised it to). It caused me to run into a delightful >> 'YouAreDeadException' which looks very related to the Garbage >> collection issues on the Troubleshooting page, as my Zookeeper session >> expired. >> >> Thanks >> >> Jamie >> >> >> >> On 7 July 2010 19:19, Jamie Cockrill <[email protected]> wrote: >>> By overcommit, do you mean make my overcommit_ratio higher on each box >>> (its at the default 50 at the moment)? What I'm noticing at the moment >>> is that hadoop is taking up the vast majority of the memory on the >>> boxes. >>> >>> I found this article: >>> http://blog.rapleaf.com/dev/2010/01/05/the-wrath-of-drwho-or-unpredictable-hadoop-memory-usage/ >>> which Todd, it looks like you replied to. Does this sound like a >>> similar problem? No worries if you can't remember, it was back in >>> january! This article suggests reducing the amount of memory allocated >>> to Hadoop at startup, how would I go about doing this? >>> >>> Thank you everyone for your patience so far. Sorry if this is taking >>> up a lot of your time. >>> >>> Thanks, >>> >>> Jamie >>> >>> On 7 July 2010 19:03, Jean-Daniel Cryans <[email protected]> wrote: >>>> swappinness at 0 is good, but also don't overcommit your memory! >>>> >>>> J-D >>>> >>>> On Wed, Jul 7, 2010 at 10:53 AM, Jamie Cockrill >>>> <[email protected]> wrote: >>>>> I think you're right. >>>>> >>>>> Unfortunately the machines are on a separate network to this laptop, >>>>> so I'm having to type everything across, apologies if it doesn't >>>>> translate well... >>>>> >>>>> free -m gave: >>>>> >>>>> Mem Total Used Free >>>>> 7992 7939 53 >>>>> b/c 7877 114 >>>>> Swap: 23415 895 22519 >>>>> >>>>> I did this on another node that isn't being smashed at the moment and >>>>> the numbers came out similar, but the buffers/cache free was higher >>>>> >>>>> vmstat -20 is giving non-zero si and so's ranging between 3 and just >>>>> short of 5000. >>>>> >>>>> That seems to be it I guess. Hadoop troubleshooting suggests setting >>>>> swappiness to 0, is that just a case of changing the value in >>>>> /proc/sys/vm/swappiness? >>>>> >>>>> thanks >>>>> >>>>> Jamie >>>>> >>>>> >>>>> >>>>> >>>>> On 7 July 2010 18:40, Todd Lipcon <[email protected]> wrote: >>>>>> On Wed, Jul 7, 2010 at 10:32 AM, Jamie Cockrill >>>>>> <[email protected]>wrote: >>>>>> >>>>>>> On the subject of GC and heap, I've left those as defaults. I could >>>>>>> look at those if that's the next logical step? Would there be anything >>>>>>> in any of the logs that I should look at? >>>>>>> >>>>>>> One thing I have noticed is that it does take an absolute age to log >>>>>>> in to the DN/RS to restart the RS once it's fallen over, in one >>>>>>> instance it took about 10 minutes. These are 8GB, 4 core amd64 boxes >>>>>>> >>>>>>> >>>>>> That indicates swapping. Can you run "free -m" on the node? >>>>>> >>>>>> Also let "vmstat 20" run while running your job and observe the "si" and >>>>>> "so" columns. If those are nonzero, it indicates you're swapping, and >>>>>> you've >>>>>> oversubscribed your RAM (very easy on 8G machines) >>>>>> >>>>>> -Todd >>>>>> >>>>>> >>>>>> >>>>>>> ta >>>>>>> >>>>>>> Jamie >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 7 July 2010 18:30, Jamie Cockrill <[email protected]> wrote: >>>>>>> > Bad news, it looks like my xcievers is set as it should be, it's in >>>>>>> > the hdfs-site.xml and looking at the job.xml of one of my jobs in the >>>>>>> > job-tracker, it's showing that property as set to 2047. I've cat | >>>>>>> > grepped one of the datanode logs and although there were a few in >>>>>>> > there, they were from a few months ago. I've upped my MAX_FILESIZE on >>>>>>> > my table to 1GB to see if that helps (not sure if it will!). >>>>>>> > >>>>>>> > Thanks, >>>>>>> > >>>>>>> > Jamie >>>>>>> > >>>>>>> > On 7 July 2010 18:12, Jean-Daniel Cryans <[email protected]> wrote: >>>>>>> >> xcievers exceptions will be in the datanodes' logs, and your problem >>>>>>> >> totally looks like it. 0.20.5 will have the same issue (since it's on >>>>>>> >> the HDFS side) >>>>>>> >> >>>>>>> >> J-D >>>>>>> >> >>>>>>> >> On Wed, Jul 7, 2010 at 10:08 AM, Jamie Cockrill >>>>>>> >> <[email protected]> wrote: >>>>>>> >>> Hi Todd & JD, >>>>>>> >>> >>>>>>> >>> Environment: >>>>>>> >>> All (hadoop and HBase) installed as of karmic-cdh3, which means: >>>>>>> >>> Hadoop 0.20.2+228 >>>>>>> >>> HBase 0.89.20100621+17 >>>>>>> >>> Zookeeper 3.3.1+7 >>>>>>> >>> >>>>>>> >>> Unfortunately my whole cluster of regionservers have now crashed, >>>>>>> >>> so I >>>>>>> >>> can't really say if it was swapping too much. There is a DEBUG >>>>>>> >>> statement just before it crashes saying: >>>>>>> >>> >>>>>>> >>> org.apache.hadoop.hbase.regionserver.wal.HLog: closing hlog writer >>>>>>> >>> in >>>>>>> >>> hdfs://<somewhere on my HDFS, in /hbase> >>>>>>> >>> >>>>>>> >>> What follows is: >>>>>>> >>> >>>>>>> >>> WARN org.apache.hadoop.hdfs.DFSClient: DataStreamer Exception: >>>>>>> >>> org.apache.hadoop.ipc.RemoteException: >>>>>>> >>> org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException: No >>>>>>> >>> lease >>>>>>> >>> on <file location as above> File does not exist. Holder >>>>>>> >>> DFSClient_-11113603 does not have any open files >>>>>>> >>> >>>>>>> >>> It then seems to try and do some error recovery (Error Recovery for >>>>>>> >>> block null bad datanode[0] nodes == null), fails (Could not get >>>>>>> >>> block >>>>>>> >>> locations. Source file "<hbase file as before>" - Aborting). There >>>>>>> >>> is >>>>>>> >>> then an ERROR org.apache...HRegionServer: Close and delete failed. >>>>>>> >>> There is then a similar LeaseExpiredException as above. >>>>>>> >>> >>>>>>> >>> There are then a couple of messages from HRegionServer saying that >>>>>>> >>> it's notifying master of its shutdown and stopping itself. The >>>>>>> >>> shutdown hook then fires and the RemoteException and >>>>>>> >>> LeaseExpiredExceptions are printed again. >>>>>>> >>> >>>>>>> >>> ulimit is set to 65000 (it's in the regionserver log, printed as I >>>>>>> >>> restarted the regionserver), however I haven't got the xceivers set >>>>>>> >>> anywhere. I'll give that a go. It does seem very odd as I did have a >>>>>>> >>> few of them fall over one at a time with a few early loads, but that >>>>>>> >>> seemed to be because the regions weren't splitting properly, so all >>>>>>> >>> the traffic was going to one node and it was being overwhelmed. >>>>>>> >>> Once I >>>>>>> >>> throttled it, after one load it a region split seemed to get >>>>>>> >>> triggered, which flung regions all over, which made subsequent loads >>>>>>> >>> much more distributed. However, perhaps the time-bomb was ticking... >>>>>>> >>> I'll have a go at specifying the xcievers property. I'm pretty >>>>>>> >>> certain i've got everything else covered, except the patches as >>>>>>> >>> referenced in the JIRA. >>>>>>> >>> >>>>>>> >>> I just grepped some of the log files and didn't get an explicit >>>>>>> >>> exception with 'xciever' in it. >>>>>>> >>> >>>>>>> >>> I am considering downgrading(?) to 0.20.5, however because >>>>>>> >>> everything >>>>>>> >>> is installed as per karmic-cdh3, I'm a bit reluctant to do so as >>>>>>> >>> presumably Cloudera has tested each of these versions against each >>>>>>> >>> other? And I don't really want to introduce further versioning >>>>>>> >>> issues. >>>>>>> >>> >>>>>>> >>> Thanks, >>>>>>> >>> >>>>>>> >>> Jamie >>>>>>> >>> >>>>>>> >>> >>>>>>> >>> On 7 July 2010 17:30, Jean-Daniel Cryans <[email protected]> >>>>>>> >>> wrote: >>>>>>> >>>> Jamie, >>>>>>> >>>> >>>>>>> >>>> Does your configuration meets the requirements? >>>>>>> >>>> >>>>>>> http://hbase.apache.org/docs/r0.20.5/api/overview-summary.html#requirements >>>>>>> >>>> >>>>>>> >>>> ulimit and xcievers, if not set, are usually time bombs that blow >>>>>>> >>>> off >>>>>>> when >>>>>>> >>>> the cluster is under load. >>>>>>> >>>> >>>>>>> >>>> J-D >>>>>>> >>>> >>>>>>> >>>> On Wed, Jul 7, 2010 at 9:11 AM, Jamie Cockrill < >>>>>>> [email protected]>wrote: >>>>>>> >>>> >>>>>>> >>>>> Dear all, >>>>>>> >>>>> >>>>>>> >>>>> My current HBase/Hadoop architecture has HBase region servers on >>>>>>> >>>>> the >>>>>>> >>>>> same physical boxes as the HDFS data-nodes. I'm getting an awful >>>>>>> >>>>> lot >>>>>>> >>>>> of region server crashes. The last thing that happens appears to >>>>>>> >>>>> be a >>>>>>> >>>>> DroppedSnapshot Exception, caused by an IOException: could not >>>>>>> >>>>> complete write to file <file on HDFS>. I am running it under load, >>>>>>> how >>>>>>> >>>>> heavy that is I'm not sure how that is quantified, but I'm >>>>>>> >>>>> guessing >>>>>>> it >>>>>>> >>>>> is a load issue. >>>>>>> >>>>> >>>>>>> >>>>> Is it common practice to put region servers on data-nodes? Is it >>>>>>> >>>>> common to see region server crashes when either the HDFS or region >>>>>>> >>>>> server (or both) is under heavy load? I'm guessing that is the >>>>>>> >>>>> case >>>>>>> as >>>>>>> >>>>> I've seen a few similar posts. I've not got a great deal of >>>>>>> >>>>> capacity >>>>>>> >>>>> to be separating region servers from HDFS data nodes, but it >>>>>>> >>>>> might be >>>>>>> >>>>> an argument I could make. >>>>>>> >>>>> >>>>>>> >>>>> Thanks >>>>>>> >>>>> >>>>>>> >>>>> Jamie >>>>>>> >>>>> >>>>>>> >>>> >>>>>>> >>> >>>>>>> >> >>>>>>> > >>>>>>> >>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> Todd Lipcon >>>>>> Software Engineer, Cloudera >>>>>> >>>>> >>>> >>> >> >
