[jira] [Commented] (KUDU-3353) Support setnx semantic on column

["ASF subversion and git services (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KUDU-3353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17603321#comment-17603321 ] 

ASF subversion and git services commented on KUDU-3353:
-------------------------------------------------------

Commit ec3a9f75b6924a70ecbf08e3805228ad9b92b9f0 in kudu's branch refs/heads/master from Yingchun Lai
[ https://gitbox.apache.org/repos/asf?p=kudu.git;h=ec3a9f75b ]

KUDU-3353 [schema] Add an immutable attribute on column schema (part 2)

This is a follow-up to b6eedb224f715ad86378a92d25f09c2084b0e2b7.
This patch includes the C++ client-side changes of the "new column
attribute IMMUTABLE" feature, including:
1. Adds a new KuduColumnSpec::Immutable() method to add IMMUTABLE
   attribute to a column, and adds a new KuduColumnSpec::Mutable()
   method to remove IMMUTABLE attribute from a column.
2. Adds a new KuduColumnSchema::is_immutable() to check if the
   attribute is set for a column schema.
3. Adds a  new KuduUpsertIgnore operation in the client API: use the
   newly added KuduTable::NewUpsertIgnore() to create a new instance
   of such operation.
4. Adds unit tests to cover the newly introduced functionality.
5. Small refactoring on the server side.

Change-Id: Id301e313eedd9cc3a494d6b4f3c14fbabe63b436
Reviewed-on: http://gerrit.cloudera.org:8080/18835
Tested-by: Yingchun Lai <ac...@gmail.com>
Reviewed-by: Alexey Serbin <al...@apache.org>


> Support setnx semantic on column
> --------------------------------
>
>                 Key: KUDU-3353
>                 URL: https://issues.apache.org/jira/browse/KUDU-3353
>             Project: Kudu
>          Issue Type: New Feature
>          Components: api, server
>            Reporter: Yingchun Lai
>            Assignee: Yingchun Lai
>            Priority: Major
>
> h1. motivation
> In some usage scenarios, Kudu table has a column with semantic of "create time", which means it represent the create timestamp of the row. The other columns have the similar semantic as before, for example, the user properties like age, address, and etc.
> Upstream and Kudu user doesn't know whether a row is exist or not, and every cell data is the lastest ingested from, for example, event stream.
> If without the "create time" column, Kudu user can use UPSERT operations to write data to the table, every columns with data will overwrite the old data. But if with the "create time" column, the cell data will be overwrote by the following UPSERT ops, which is not what we expect.
> To achive the goal, we have to read the column out to judge whether the column is NULL or not, if it's NULL, we can fill the row with the cell, if not NULL, we will drop it from the data before UPSERT, to avoid overwite "create time".
> It's expensive, is there a way to avoid a read from Kudu?
> h1. Resolvation
> We can implement column schema with semantic of "update if null". That means cell data in changelist will update the base data if the latter is NULL, and will ignore updates if it is not NULL.
> So we can use Kudu similarly as before, but only defined the column as "update if null" when create table or add column.
>  



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