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From "Liu, Ming (Ming)" <ming....@esgyn.cn>
Subject RE: Why are tables in "_MD_" all using HBase format?
Date Wed, 15 Nov 2017 16:11:13 GMT
thanks Anoop for the details. I hope we can plan this in R2.3.

Thanks,
Ming

-----Original Message-----
From: Anoop Sharma [mailto:anoop.sharma@esgyn.com] 
Sent: Wednesday, November 15, 2017 11:58 PM
To: dev@trafodion.incubator.apache.org
Subject: RE: Why are tables in "_MD_" all using HBase format?

In the beginning, there was support for only HBase/Cell format tables. 
Aligned format was added later.

Since metadata could have been created prior to aligned format, it
was created in HBase format. Metadata created later could not be in
aligned format as that would cause compatibility issues. Since metadata
definitions are hardcoded, they must match how data is stored in
actual metadata tables.

To properly change metadata format from HBase to Aligned, upgrade
has to be enhanced. During upgrade, it would internally create metadata in 
aligned format and then move data from old MD to new MD. 
This is something that is in plans but need to be coordinated as metadata
upgrade should only happen at major releases.

anoop


-----Original Message-----
From: Liu, Ming (Ming) [mailto:ming.liu@esgyn.cn] 
Sent: Wednesday, November 15, 2017 5:45 AM
To: dev@trafodion.incubator.apache.org
Subject: RE: Why are tables in "_MD_" all using HBase format?

I realized that even I modified the DDL in CmpSeabaseDDLmd.h for those tables to use 'aligned
format', but the tables are still in 'hbase format'. So everything works fine.
It seems need a lot of work to change it into 'aligned format'.

Thanks,
Ming

-----Original Message-----
From: Liu, Ming (Ming) [mailto:ming.liu@esgyn.cn] 
Sent: Wednesday, November 15, 2017 9:03 PM
To: dev@trafodion.incubator.apache.org
Subject: Why are tables in "_MD_" all using HBase format?

hi, all,

I am developing the SSCC code and meet problems on DDL operations. I noticed all "_MD_" tables
are created in "hbase format", is there any special reason that Trafodion must use "hbase
format" for these metadata tables?
I tried to use "aligned format", and it seems working as well.
So I am wondering if there are some reasons that we HAVE TO use "hbase format" here, if not,
shall we use aligned format for these tables?

thanks,
Ming

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