[jira] [Commented] (CASSANDRA-16737) ALTER ... ADD can increase the number of SSTables being read

["Benjamin Lerer (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-16737?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17372718#comment-17372718 ] 

Benjamin Lerer commented on CASSANDRA-16737:
--------------------------------------------

[~e.dimitrova], [~maedhroz] I modified the KeyCache tests to clarify from where were coming the expected numbers.
Thanks a lot for the reviews.

> ALTER ... ADD can increase the number of SSTables being read
> ------------------------------------------------------------
>
>                 Key: CASSANDRA-16737
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16737
>             Project: Cassandra
>          Issue Type: Bug
>          Components: CQL/Semantics
>            Reporter: Benjamin Lerer
>            Assignee: Benjamin Lerer
>            Priority: Normal
>             Fix For: 3.11.x, 4.0.x
>
>          Time Spent: 2h 20m
>  Remaining Estimate: 0h
>
> With the following SSTables:
> {code:java}
> CREATE TABLE my_table (pk int, ck int, v1 int, PRIMARY KEY(pk, ck))
> INSERT INTO my_table (pk, ck, v1) VALUES (1, 1, 1) USING TIMESTAMP 1000;
> --> flush()
> INSERT INTO my_table (pk, ck, v1) VALUES (1, 1, 2) USING TIMESTAMP 2000;
> --> flush()
> INSERT INTO my_table  (pk, ck, v1) VALUES (1, 1, 3) USING TIMESTAMP 3000
> --> flush()
> {code}
> the following query:
> {code:java}
> SELECT pk, ck, v1 FROM my_table WHERE pk = 1 AND ck = 1{code}
> will only read the third SSTable.
> If we add a column to the table (e.g. {{ALTER TABLE my_table ADD v2 int}}) and rerun the query, the query will read the 3 SSTables.
> The reason for this behavior is due to the fact that C* is trying to read all the {{fetched}} columns to ensure that it will return a row if at least one of its column is non null.
> In practice for CQL tables, C* does not need to fetch all columns if the row contains a primary key liveness as it is enough to guaranty that the row exists. By consequence, even after the addition of the new column C* should read only the third SSTable.



--
This message was sent by Atlassian Jira
(v8.3.4#803005)

---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscribe@cassandra.apache.org
For additional commands, e-mail: commits-help@cassandra.apache.org