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Re: Mview in cassandra


The error might be related to your specific clusters (sstableloader / 1 node), I imagine connectivity might be wrong or the data not be loaded properly for some reason. The data has to be available (nodes up - and maybe 'nodetool refresh'/'cassandra restart' after the sstableloader things) and able to connect to each other. 

I tried to drop the Materialized View and recreate it , but the data is not getting populated with version 3.11.1

What error do you have then, when recreating (if any)? 
Are normal reads working? And when using a consistency of 'all'? 

I was overall willing to share this information that might matter to you about MVs:
The recommendation around Materialized view at the moment is as follow:
"Do not use them unless you know exactly how they (don't) work."

According to Blake (but I think there is a large consensus on this opinion):

Concerns about MV’s suitability for production are not uncommon, and this just formalizes
the advice often given to people considering materialized views. That is: materialized views
have shortcomings that can make them unsuitable for the general use case. If you’re not
familiar with their shortcomings and confident they won’t cause problems for your use case,
you shouldn’t use them 
The shortcomings I’m referring to are:
* There's no way to determine if a view is out of sync with the base table.
* If you do determine that a view is out of sync, the only way to fix it is to drop and rebuild
the view.
Even in the happy path, there isn’t an upper bound on how long it will take for updates
to be reflected in the view.

It was even shared that the feature is complex and that we (community, but I think also committers and developers) don't have a complete understanding of this feature.
You might want to consider to look for a workaround not involving MVs. Also, version C*3.11.2 do not seem to have any improvement regarding MV compared to C*3.11.1, it was just marked as experimental it seems. Thus upgrading will not help probably.

I imagine it's not what you wanted to hear, but I would really not stick with MVs at the moment. If this cluster would be under my responsibility I would probably consider redesign the schema.

Alain Rodriguez - alain@xxxxxxxxxxxxxxxxx
France / Spain

The Last Pickle - Apache Cassandra Consulting

Le mar. 16 oct. 2018 à 18:25, rajasekhar kommineni <rajacoast@xxxxxxxxx> a écrit :

I am seeing below warning message in system.log after datacopy using sstabloader.

WARN  [CompactionExecutor:972] 2018-10-15 22:20:39,308 ViewBuilder.java:189 - Materialized View failed to complete, sleeping 5 minutes before restarting
org.apache.cassandra.exceptions.UnavailableException: Cannot achieve consistency level ONE

I tried to drop the Materialized View and recreate it , but the data is not getting populated with version 3.11.1

I tried the same on version 3.11.2 on single node dev box and I can query the Materialized View with data. Any body have some experiences with Mview’s.


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