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Yingchun Lai commented on KUDU-3353: ------------------------------------ This feature has been implemented by [KUDU-3353 [schema] Add an immutable attribute on column schema (If80ebca7) · Gerrit Code Review (cloudera.org)|https://gerrit.cloudera.org/c/18241/], Help to review, thanks! [~anjuwong] [~aserbin] [~tlipcon] > 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. > -- This message was sent by Atlassian Jira (v8.20.7#820007)