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From Joe Obernberger <joseph.obernber...@gmail.com>
Subject Re: Recovery Issue - Solr 6.6.1 and HDFS
Date Tue, 21 Nov 2017 20:07:47 GMT
We've never run an index this size in anything but HDFS, so I have no 
comparison.  What we've been doing is keeping two main collections - all 
data, and the last 30 days of data.  Then we handle queries based on 
date range.  The 30 day index is significantly faster.

My main concern right now is that 6 of the 100 shards are not coming 
back because of no leader.  I've never seen this error before.  Any 
ideas?  ClusterStatus shows all three replicas with state 'down'.

Thanks!

-joe


On 11/21/2017 2:35 PM, Hendrik Haddorp wrote:
> We actually also have some performance issue with HDFS at the moment. 
> We are doing lots of soft commits for NRT search. Those seem to be 
> slower then with local storage. The investigation is however not 
> really far yet.
>
> We have a setup with 2000 collections, with one shard each and a 
> replication factor of 2 or 3. When we restart nodes too fast that 
> causes problems with the overseer queue, which can lead to the queue 
> getting out of control and Solr pretty much dying. We are still on 
> Solr 6.3. 6.6 has some improvements and should handle these actions 
> faster. I would check what you see for 
> "/solr/admin/collections?action=OVERSEERSTATUS&wt=json". The critical 
> part is the "overseer_queue_size" value. If this goes up to about 
> 10000 it is pretty much game over on our setup. In that case it seems 
> to be best to stop all nodes, clear the queue in ZK and then restart 
> the nodes one by one with a gap of like 5min. That normally recovers 
> pretty well.
>
> regards,
> Hendrik
>
> On 21.11.2017 20:12, Joe Obernberger wrote:
>> We set the hard commit time long because we were having performance 
>> issues with HDFS, and thought that since the block size is 128M, 
>> having a longer hard commit made sense.  That was our hypothesis 
>> anyway.  Happy to switch it back and see what happens.
>>
>> I don't know what caused the cluster to go into recovery in the first 
>> place.  We had a server die over the weekend, but it's just one out 
>> of ~50.  Every shard is 3x replicated (and 3x replicated in HDFS...so 
>> 9 copies).  It was at this point that we noticed lots of network 
>> activity, and most of the shards in this recovery, fail, retry loop.  
>> That is when we decided to shut it down resulting in zombie lock files.
>>
>> I tried using the FORCELEADER call, which completed, but doesn't seem 
>> to have any effect on the shards that have no leader. Kinda out of 
>> ideas for that problem.  If I can get the cluster back up, I'll try a 
>> lower hard commit time.  Thanks again Erick!
>>
>> -Joe
>>
>>
>> On 11/21/2017 2:00 PM, Erick Erickson wrote:
>>> Frankly with HDFS I'm a bit out of my depth so listen to Hendrik ;)...
>>>
>>> I need to back up a bit. Once nodes are in this state it's not
>>> surprising that they need to be forcefully killed. I was more thinking
>>> about how they got in this situation in the first place. _Before_ you
>>> get into the nasty state how are the Solr nodes shut down? Forcefully?
>>>
>>> Your hard commit is far longer than it needs to be, resulting in much
>>> larger tlog files etc. I usually set this at 15-60 seconds with local
>>> disks, not quite sure whether longer intervals are helpful on HDFS.
>>> What this means is that you can spend up to 30 minutes when you
>>> restart solr _replaying the tlogs_! If Solr is killed, it may not have
>>> had a chance to fsync the segments and may have to replay on startup.
>>> If you have openSearcher set to false, the hard commit operation is
>>> not horribly expensive, it just fsync's the current segments and opens
>>> new ones. It won't be a total cure, but I bet reducing this interval
>>> would help a lot.
>>>
>>> Also, if you stop indexing there's no need to wait 30 minutes if you
>>> issue a manual commit, something like
>>> .../collection/update?commit=true. Just reducing the hard commit
>>> interval will make the wait between stopping indexing and restarting
>>> shorter all by itself if you don't want to issue the manual commit.
>>>
>>> Best,
>>> Erick
>>>
>>> On Tue, Nov 21, 2017 at 10:34 AM, Hendrik Haddorp
>>> <hendrik.haddorp@gmx.net> wrote:
>>>> Hi,
>>>>
>>>> the write.lock issue I see as well when Solr is not been stopped 
>>>> gracefully.
>>>> The write.lock files are then left in the HDFS as they do not get 
>>>> removed
>>>> automatically when the client disconnects like a ephemeral node in
>>>> ZooKeeper. Unfortunately Solr does also not realize that it should 
>>>> be owning
>>>> the lock as it is marked in the state stored in ZooKeeper as the 
>>>> owner and
>>>> is also not willing to retry, which is why you need to restart the 
>>>> whole
>>>> Solr instance after the cleanup. I added some logic to my Solr 
>>>> start up
>>>> script which scans the log files in HDFS and compares that with the 
>>>> state in
>>>> ZooKeeper and then delete all lock files that belong to the node 
>>>> that I'm
>>>> starting.
>>>>
>>>> regards,
>>>> Hendrik
>>>>
>>>>
>>>> On 21.11.2017 14:07, Joe Obernberger wrote:
>>>>> Hi All - we have a system with 45 physical boxes running solr 
>>>>> 6.6.1 using
>>>>> HDFS as the index.  The current index size is about 31TBytes. With 3x
>>>>> replication that takes up 93TBytes of disk. Our main collection is 
>>>>> split
>>>>> across 100 shards with 3 replicas each.  The issue that we're 
>>>>> running into
>>>>> is when restarting the solr6 cluster.  The shards go into recovery 
>>>>> and start
>>>>> to utilize nearly all of their network interfaces.  If we start 
>>>>> too many of
>>>>> the nodes at once, the shards will go into a recovery, fail, and 
>>>>> retry loop
>>>>> and never come up.  The errors are related to HDFS not responding 
>>>>> fast
>>>>> enough and warnings from the DFSClient.  If we stop a node when 
>>>>> this is
>>>>> happening, the script will force a stop (180 second timeout) and upon
>>>>> restart, we have lock files (write.lock) inside of HDFS.
>>>>>
>>>>> The process at this point is to start one node, find out the lock 
>>>>> files,
>>>>> wait for it to come up completely (hours), stop it, delete the 
>>>>> write.lock
>>>>> files, and restart.  Usually this second restart is faster, but it 
>>>>> still can
>>>>> take 20-60 minutes.
>>>>>
>>>>> The smaller indexes recover much faster (less than 5 minutes). 
>>>>> Should we
>>>>> have not used so many replicas with HDFS?  Is there a better way 
>>>>> we should
>>>>> have built the solr6 cluster?
>>>>>
>>>>> Thank you for any insight!
>>>>>
>>>>> -Joe
>>>>>
>>> ---
>>> This email has been checked for viruses by AVG.
>>> http://www.avg.com
>>>
>>
>


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