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Column family documentation is extremely sparse #652

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georgelorchpercona opened this issue Jul 12, 2017 · 3 comments

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@georgelorchpercona
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commented Jul 12, 2017

There doesn't seem to be a lot of documentation on the uses and limitations of column families. How do we explicitly create and set options, how do we (or can we) explicitly delete one? Can we and how do we move indexes/tables from one cf to another, etc...

@alxyang

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commented Jul 12, 2017

You are right that a lot more documentation is needed here.

How do we explicitly create and set options?
see test case rocksdb.rocksdb_cf_options for example usage. We also introduced recently rocksdb_update_cf_options variable for when you want to update cf options dynamically. (See 4854351)

How can we delete column families?
This isn't supported yet from MyRocks, we have discussed it internally and plan to work on it in the future. Is there a particular reason you need this? If urgent, we could look into it sooner.

How can we move indexes/tables from one cf to another?
The cf is specified by the comment in the index. To move the index/table from one cf to another, you must perform an alter table, and change the cf comment of the particular index.
e.g. DROP INDEX example on t1, ADD INDEX example on t1 comment='new cf'

Other members of the team can chime in here. If you have any other questions let us know and we'll try to answer.

@georgelorchpercona

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commented Jul 12, 2017

Thanks Alex, these were just examples of typical user scenarios that are not documented very clearly in the wiki. The reason I posted the issue is that our doc team will need this info in order to correctly document how to understand, manage, and work with column families within MySQL/Percona Server.

@RoelVdP

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commented Jul 14, 2017

@alxyang Thank you for your comment. So this raises many more interesting questions;

  1. Can cf be dynamically changed as far as compression algo's go?
  2. Would it make sense to add some dynamic changes (like DROP INDEX/ADD INDEX and ALTER) in the testcase in 4854351 ?
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