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From Emir Arnautović <emir.arnauto...@sematext.com>
Subject Re: Solr node is out of sync (looks Healthy)
Date Mon, 12 Feb 2018 22:56:57 GMT
Hi Daniel,
Please see inline comments.
--
Monitoring - Log Management - Alerting - Anomaly Detection
Solr & Elasticsearch Consulting Support Training - http://sematext.com/



> On 12 Feb 2018, at 13:13, Daniel Carrasco <d.carrasco@i2tic.com> wrote:
> 
> Hello,
> 
> 2018-02-12 12:32 GMT+01:00 Emir Arnautović <emir.arnautovic@sematext.com <mailto:emir.arnautovic@sematext.com>>:
> 
>> Hi Daniel,
>> Maybe it is Monday and I am still not warmed up, but your details seems a
>> bit imprecise to me. Maybe not directly related to your problem, but just
>> to exclude that you are having some strange Solr setup, here is my
>> understanding: You are running a single SolrCloud cluster with 8 nodes. It
>> has a single collection with X shards and Y replicas. You use DIH to index
>> data and you use curl to interact with Solr and start DIH process. You see
>> some of replicas for some of shards having less data and after node restart
>> it ends up being ok.
> 
> 
>> Is this right? If it is, what is X and Y?
> 
> 
> Near to reality:
> 
>   - I've a SolrCloud cluster with 8 nodes but has multiple collections.
>   - Every collection has only one shard for performance purpose (I did
>   some test splitting shards and queries were slower).
Distributed request comes with an overhead and if collection is small, that overhead can be
larger than benefit of parallelising search.

>   - Every collection has 8 replicas (one by node)
I would compare all shards on all nodes (64 Solr cores) v.s. having just one replica (16 Solr
cores)

>   - After restart the node it start to recover the collections. I don't
>   know if Solr serve data directly on that state or get the data from other
>   nodes before serve it, but even while is recovering, the data looks OK.
Recovery can be from transaction logs (logs can tell) and that would mean that there was no
hard commit after some updates.

> 
> 
> 
>> Do you have autocommit set up or you commit explicitly?
> 
> 
> I'm not sure about that. How I can check it?
It is part of solr.xml

> 
> On curl command is not specified, but will be true by default, right?
I think it is for full import.

> 
> 
> 
>> Did you check logs on node with less data and did you see any
>> errors/warnings?
> 
> 
> I'm not sure when it failed and the cluster has a lot warnings and error
> every time (maybe related with queries from shop), so is hard to determine
> if import error exists and what's the error related to the import. Is like
> search a needle on a haystack
Not with some logging solution - one such is Sematext’s Logsene: https://sematext.com/logsene/
<https://sematext.com/logsene/>

> 
> 
>> Do you do full imports or incremental imports?
>> 
> 
> I've checked the curl command and looks like is doing full imports without
> clean data:
> http://' <http://'/> . $solr_ip .
> ':8983/solr/descriptions/dataimport?command=full-import&clean=false&entity=description_’.$idm[$j].'_lastupdate
This is not a good strategy since Solr does not have real updates - it is delete + insert
and deleted documents are purged on segment merges. Also this will not eliminate documents
that are deleted in the primary storage. It is much better to index it in new collection and
use aliases to point to used collection. This way you can even roll back if not happy with
new index.

> 
> 
>> 
>> Not related to issue, but just a note that Solr does not guaranty
>> consistency at any time - it has something called “eventual consistency” -
>> once updates stop all replicas will (should) end up in the same state.
>> Having said that, using Solr results directly in your UI would either
>> require you to cache used documents on UI/middle layer or implement some
>> sort of stickiness or retrieve only ID from Solr and load data from primary
>> storage. If you have static data, and you update index once a day, you can
>> use aliases and switch between new and old index and you will suffer from
>> this issue only at the time when doing switches.
>> 
> 
> But is normal that data will be inconsistent for a very long time?, because
> looks like the data is inconsistent from about a week…
It will become consistent once all changes are committed and searchers reopened.

> 
> Another question: With HDFS, data will be consistent?. With HDFS the data
> will be shared between nodes and then updates will be avaible on all nodes
> at same time, right?
I am not too familiar with running Solr on HDFS, but I doubt that it is working the way you
expect it to work. You might be able to have multiple Solr instances (not part of the same
cluster - can be standalone Solr) reading from the same HDFS directory and one updating it,
but you would probably have to reload core on read instances to be aware of changes. Not sure
if you would get much out of it - just different replication mechanism. But it is late here
and I never used Solr on HDFS so take this with a grain of salt.

> 
> Thanks!!
> 
> 
>> 
>> Regards,
>> Emir
>> --
>> Monitoring - Log Management - Alerting - Anomaly Detection
>> Solr & Elasticsearch Consulting Support Training - http://sematext.com/
>> 
>> 
>> 
>>> On 12 Feb 2018, at 12:00, Daniel Carrasco <d.carrasco@i2tic.com> wrote:
>>> 
>>> Hello, thanks for your help.
>>> 
>>> I answer bellow.
>>> 
>>> Greetings!!
>>> 
>>> 2018-02-12 11:31 GMT+01:00 Emir Arnautović <emir.arnautovic@sematext.com
>> <mailto:emir.arnautovic@sematext.com <mailto:emir.arnautovic@sematext.com>>>:
>>> 
>>>> Hi Daniel,
>>>> Can you tell us more about your document update process. How do you
>> commit
>>>> changes? Since it got fixed after restart, it seems to me that on that
>> one
>>>> node index searcher was not reopened after updates. Do you see any
>>>> errors/warnings on that node?
>>>> 
>>> 
>>> i've asked to the programmers and looks like they are using the
>> collections
>>> dataimport using curl. I think the data is imported from a Microsoft SQL
>>> server using a solr plugin.
>>> 
>>> 
>>>> Also, what do you mean by “All nodes are standalone”?
>>>> 
>>> 
>>> I mean that nodes don't share filesystem (I'm planning to use Hadoop, but
>>> I've to learn to create and maintain the cluster first). All nodes has
>> its
>>> own data drive and are connected to the cluster using zookeeper.
>>> 
>>> 
>>>> 
>>>> Regards,
>>>> Emir
>>>> --
>>>> Monitoring - Log Management - Alerting - Anomaly Detection
>>>> Solr & Elasticsearch Consulting Support Training - http://sematext.com/
>>>> 
>>>> 
>>>> 
>>>>> On 12 Feb 2018, at 11:16, Daniel Carrasco <d.carrasco@i2tic.com>
>> wrote:
>>>>> 
>>>>> Hello,
>>>>> 
>>>>> We're using Solr to manage products data on our shop and the last week
>>>> some
>>>>> customers called us telling that price between shop and shopping basket
>>>>> differs. After research a bit I've noticed that it happens sometimes
on
>>>>> page refresh.
>>>>> After disabling all cache I've queried all solr instances to see if
>> data
>>>> is
>>>>> correct and I've seen that one of them give a different price for the
>>>>> product, so looks like the instance has not got the updated data.
>>>>> 
>>>>> - How is possible that a node on a cluster have different data?
>>>>> - How i can check if data is in sync?, because the cluster looks al
>>>>> healthy on admin, and the node is active and OK.
>>>>> - Is there any way to detect this error? and How I can force resyncs?
>>>>> 
>>>>> After restart the node it got synced, so the data now is OK, but I
>> can't
>>>>> restart the nodes every time to see if data is right (it tooks a lot
of
>>>>> time to be synced again).
>>>>> 
>>>>> My configuration is: 8 Solr nodes using v7.1.0 and zookeeper v3.4.11.
>> All
>>>>> nodes are standalone (I'm not using hadoop).
>>>>> 
>>>>> Thanks and greetings!
>>>>> --
>>>>> _________________________________________
>>>>> 
>>>>>    Daniel Carrasco Marín
>>>>>    Ingeniería para la Innovación i2TIC, S.L.
>>>>>    Tlf:  +34 911 12 32 84 Ext: 223 <+34%20911%2012%2032%2084>
>>>>>    www.i2tic.com <http://www.i2tic.com/> <http://www.i2tic.com/
<http://www.i2tic.com/>>
>>>>> _________________________________________
>>>> 
>>>> 
>>> 
>>> 
>>> --
>>> _________________________________________
>>> 
>>>     Daniel Carrasco Marín
>>>     Ingeniería para la Innovación i2TIC, S.L.
>>>     Tlf:  +34 911 12 32 84 Ext: 223
>>>     www.i2tic.com <http://www.i2tic.com/> <http://www.i2tic.com/ <http://www.i2tic.com/>>
>>> _________________________________________
>> 
>> 
> 
> 
> -- 
> _________________________________________
> 
>      Daniel Carrasco Marín
>      Ingeniería para la Innovación i2TIC, S.L.
>      Tlf:  +34 911 12 32 84 Ext: 223
>      www.i2tic.com <http://www.i2tic.com/>
> _________________________________________


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