I got this working, did a hard kill of regionserver, and it worked. I used the hadoop/hdfs/branches/HDFS-265 branch and was banging my head trying to get it work. Saw that hlog was reflectively calling SequenceFile.Writer.syncFs(). This method did not exist (in hadoop/common/branches/branch-0.21), so I naively changed it to call sync(). But this is a different kind of sync...
To get it to work I added the Writer.syncFs() method which just calls out.sync(). On Sat, Aug 8, 2009 at 7:51 PM, Andrew Purtell <[email protected]> wrote: > I realized too late I was not running Hadoop with DEBUG, only HBase. > > I'll try again next month, when it will not hurt to lose data. > > - Andy > > > > > ________________________________ > From: stack <[email protected]> > To: [email protected] > Sent: Saturday, August 8, 2009 6:34:07 PM > Subject: Re: append (hadoop-4379), was -> Re: roadmap: data integrity > > Didn't mean to be so short. I'd suggest that it would be good putting your > experience up in HDFS-200/HADOOP-4379. Lads there'd be interested in what > you've found. > St.Ack > > On Sat, Aug 8, 2009 at 9:36 AM, Andrew Purtell <[email protected]> > wrote: > > > Cluster down hard after RS failure. Master stuck indefinitely splitting > > logs. > > Endless instances of this message, once per second: > > > > org.apache.hadoop.hdfs.DFSClient: Could not complete file > > /hbase/content/1965559571/oldlogfile.lo retrying... > > > > Turning off "dfs.support.append". > > > > - Andy > > > > > > > > > > ________________________________ > > From: stack <[email protected]> > > To: [email protected] > > Sent: Friday, August 7, 2009 12:34:40 PM > > Subject: Re: append (hadoop-4379), was -> Re: roadmap: data integrity > > > > You are a good man Andrew. > > St.Ack > > > > On Fri, Aug 7, 2009 at 10:27 AM, Andrew Purtell <[email protected]> > > wrote: > > > > > I'm going to join you in testing this stack, taking the below as config > > > recipe. > > > > > > - Andy > > > > > > > > > > > > > > > ________________________________ > > > From: stack <[email protected]> > > > To: [email protected] > > > Sent: Friday, August 7, 2009 9:54:53 AM > > > Subject: append (hadoop-4379), was -> Re: roadmap: data integrity > > > > > > Here is a quick note on the current state of my testing of HADOOP-4379 > > > (support for 'append' in hadoop 0.20.x). > > > > > > On my small test cluster, I am not able to break the latest patch > posted > > by > > > Dhruba under heavy-loadings. It seems to basically work. On > > regionserver > > > crash, the master runs log split and when it comes to the last in the > set > > > of > > > regionserver logs for splitting, the one that is inevitably unclosed > > > because > > > the process crashed, we are able to recover most edits in this last > file > > > (in > > > my testing, it seemed to be all edits up to the last flush of the > > > regionserver process). > > > > > > The upshot is that tentatively, we may have a "working" append in the > > 0.20 > > > timeframe (In 0.21, we should have > > > https://issues.apache.org/jira/browse/HDFS-265). I'll keep testing > but > > > I'd > > > suggest its time for others to try out. > > > > > > With HADOOP-4379, the process recovering non-closed log files -- the > > master > > > in our case -- must successfully open the file in append mode and then > > > close > > > it. Once closed, new readers can purportedly see up to the last flush. > > > The > > > open to append can take a little while before it will go through > > (Complaint > > > is that another process holds the files' lease). Meantime, the opening > > for > > > append process must retry. In my experience its taking 2-10 seconds. > > > > > > Support for appends is off by default in hadoop even after HADOOP-4379 > > has > > > been applied. To enable, you need to set dfs.support.append. Set it > > > everywhere -- all over hadoop and in hbase-site.xml so hbase/DFSClient > > can > > > see the attribute. > > > > > > HBase TRUNK will recognize if the bundled hadoop supports append via > > > introspection (SequenceFile has a new syncFs method when HADOOP-4379 > has > > > been applied). If an append-supporting hadoop is present, and > > > dfs.support.append is set in hbase context, then hbase when its running > > > HLog#splitLog will try to opening files to append. On regionserver > > crash, > > > you can see the master HLog#splitLog loop retrying the open for append > > > until > > > it is successful (You'll see in the master log complaint that lease on > > the > > > file is held by another process). We retry every second. > > > > > > Successful recovery of all edits is uncovering new, interesting issues. > > In > > > my testing I was killing regionserver only but also killing > regionserver > > > and > > > datanode. In latter case, what I would see is that namenode would > > continue > > > to assign the dead namenode work at least until its lease expired. > Fair > > > enough says you, only the datanode lease is ten minutes by default. I > > set > > > it down in my tests using heartbeat.recheck.interval (There is a > pregnant > > > comment in HADOOP-4379 w/ clientside code where Ruyue Ma says they get > > > around this issue by having client pass the namenode the datanodes it > > knows > > > dead when asking for an extra block). We might want to recommend > setting > > > it > > > down in general. > > > > > > Other issues are hbase bugs we see when edits all recovered. I've been > > > filing issues on these over last few days. > > > > > > St.Ack > > > > > > > > > > > > > > > > > > On Fri, Aug 7, 2009 at 9:03 AM, Andrew Purtell <[email protected]> > > > wrote: > > > > > > > Good to see there's direct edit replication support; that can make > > > > things easier. > > > > > > > > I've seen people use DRDB or NFS to replicate edits currently. > > > > > > > > Namenode failover is a "solvable" issue with traditional HA: OS level > > > > heartbeats, fencing, fail over -- e.g. HA infrastructure daemon > starts > > > > NN instance on node B if heartbeat from node A is lost and takes a > > > > power control operation on A to make sure it is dead. On both nodes > the > > > > infastructure daemons trigger the OS watchdog if the NN process dies. > > > > Combine this with automatic IP address reassignment. Then, page the > > > > operators. Add another node C for additional redundancy, and make > sure > > > > all of the alternatives are on separate racks and power rails, and > make > > > > sure the L2 and L3 topology is also HA (e.g. bonded ethernet to > > > > redundant switches at L2, mesh routing at L3, etc.) If the cluster is > > > > not super huge it can all be spanned at L2 over redundant switches. > L3 > > > > redundancy is tricker. A typical configuration could have a lot of > OSPF > > > > stub networks -- depends how L2 is partitoned -- which can make the > > > > routing table difficult for operators to sort out. > > > > > > > > I've seen this type of thing work for myself, ~15 seconds from > > > > (simulated) fault on NN node A to the new NN up and responding to DN > > > > reconnections on node B, with 0.19. > > > > > > > > You can build in additional assurance of fast failover by building > > > > redundant processes to run concurrently with a few datanodes which > over > > > > and over ping the NN via the namenode protocol and trigger fencing > and > > > > failover if it stops responding. > > > > > > > > One wrinkle is the new namenode starts up in safe mode. As long as > > > > HBase can handle temporary periods where the cluster goes into > > > > safemode after NN fail over, it can ride it out. > > > > > > > > This is ugly, but this is I believe an accepted and valid systems > > > > engineering solution for the NN SPOF issue for the folks I mentioned > > > > in my previous email, something they would be familiar with. Edit > > > > replication support in HDFS 0.21 makes it a little less work to > > > > achieve and maybe a little faster to execute, so that's an > > > > improvement. > > > > > > > > It may be overstating it a little bit to say that the NN SPOF is not > a > > > > concern for HBase, but, in my opinion, we need to address WAL and > > > > (lack of FSCK) issues first before being concerned about it. HBase > can > > > > lose data all on its own. > > > > > > > > - Andy > > > > > > > > > > > > > > > > > > > > > > > > ________________________________ > > > > From: Jean-Daniel Cryans <[email protected]> > > > > To: [email protected] > > > > Sent: Friday, August 7, 2009 3:25:19 AM > > > > Subject: Re: roadmap: data integrity > > > > > > > > https://issues.apache.org/jira/browse/HADOOP-4539 > > > > > > > > This issue was closed long ago. But, Steve Loughran just said on tha > > > > hadoop mailing list that the new NN has to come up with the same > > > > IP/hostname as the failed one. > > > > > > > > J-D > > > > > > > > On Fri, Aug 7, 2009 at 2:37 AM, Ryan Rawson<[email protected]> > wrote: > > > > > WAL is a major issue, but another one that is coming up fast is the > > > > > SPOF that is the namenode. > > > > > > > > > > Right now, namenode aside, I can rolling restart my entire cluster, > > > > > including rebooting the machines if I needed to. But not so with > the > > > > > namenode, because if it does AWOL, all sorts of bad can happen. > > > > > > > > > > I hope that HDFS 0.21 addresses both these issues. Can we get > > > > > positive confirmation that this is being worked on? > > > > > > > > > > -ryan > > > > > > > > > > On Thu, Aug 6, 2009 at 10:25 AM, Andrew Purtell< > [email protected]> > > > > wrote: > > > > >> I updated the roadmap up on the wiki: > > > > >> > > > > >> > > > > >> * Data integrity > > > > >> * Insure that proper append() support in HDFS actually closes > the > > > > >> WAL last block write hole > > > > >> * HBase-FSCK (HBASE-7) -- Suggest making this a blocker for > 0.21 > > > > >> > > > > >> I have had several recent conversations on my travels with people > in > > > > >> Fortune 100 companies (based on this list: > > > > >> http://www.wageproject.org/content/fortune/index.php). > > > > >> > > > > >> You and I know we can set up well engineered HBase 0.20 clusters > > that > > > > >> will be operationally solid for a wide range of use cases, but > given > > > > >> those aforementioned discussions there are certain sectors which > > would > > > > >> say HBASE-7 is #1 before HBase is "bank ready". Not until we can > > say: > > > > >> > > > > >> - Yes, when the client sees data has been committed, it actually > > has > > > > >> been written and replicated on spinning or solid state media in > all > > > > >> cases. > > > > >> > > > > >> - Yes, we go to great lengths to recover data if ${deity} forbid > > you > > > > >> crush some underprovisioned cluster with load or some bizarre bug > or > > > > >> system fault happens. > > > > >> > > > > >> HBASE-1295 is also required for business continuity reasons, but > > this > > > > >> is already a priority item for some HBase committers. > > > > >> > > > > >> The question is I think does the above align with project goals. > > > > >> Making HBase-FSCK a blocker will probably knock something someone > > > > >> wants for the 0.21 timeframe off the list. > > > > >> > > > > >> - Andy > > > > >> > > > > >> > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
