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From "Krishna Dattu Koneru (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13657) Materialized Views: Index MV on TTL'ed column produces orphanized view entry if another column keeps entry live
Date Thu, 06 Jul 2017 06:01:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16075985#comment-16075985
] 

Krishna Dattu Koneru commented on CASSANDRA-13657:
--------------------------------------------------

This happens because of how the row expiry works . Row exists as long as cells (even non-pk)
are live.
For example, below table (MV is also a table, just maintained by cassandra automatically.)

 {code}
 CREATE TABLE t (k int, a int, b int, PRIMARY KEY (k,a));
 insert into t (k,a) VALUES (1,1) using ttl 10;
 update t using ttl 60 set b=1 where k=1 and a=1;

--- wait for 10 seconds.

select k,a,b,ttl(b) from t;

 k | a | b | ttl(b)
---+---+---+--------
 1 | 1 | 1 |     45

(1 rows)
 {code}

Row does not expire as {{b}} is still alive. 


This causes problem for materialized views.column from base table expires and view row still
exists. View row should expire because, base row will no longer match the mandatory {{IS NOT
NULL}} filter on PK columns.

I made a patch to make sure that non-primary key columns don't outlive view pk columns.


||Patch||Circleci||
|[trunk|https://github.com/apache/cassandra/compare/trunk...krishna-koneru:CASSANDRA-13657-trunk]|[test|https://circleci.com/gh/krishna-koneru/cassandra/24]|

Comments appreciated. 

( I am not sure if there is a way to fix already orphanized view entries )

> Materialized Views: Index MV on TTL'ed column produces orphanized view entry if another
column keeps entry live
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13657
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13657
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Materialized Views
>            Reporter: Fridtjof Sander
>            Assignee: Krishna Dattu Koneru
>
> {noformat}
> CREATE TABLE t (k int, a int, b int, PRIMARY KEY (k));
> CREATE MATERIALIZED VIEW mv AS SELECT * FROM t WHERE k IS NOT NULL AND a IS NOT NULL
PRIMARY KEY (a, k);
> INSERT INTO t (k) VALUES (1);
> UPDATE t USING TTL 5 SET a = 10 WHERE k = 1;
> UPDATE t SET b = 100 WHERE k = 1;
> SELECT * from t; SELECT * from mv;
>  k | a  | b
> ---+----+-----
>  1 | 10 | 100
> (1 rows)
>  a  | k | b
> ----+---+-----
>  10 | 1 | 100
> (1 rows)
> -- 5 seconds later
> SELECT * from t; SELECT * from mv;
>  k | a    | b
> ---+------+-----
>  1 | null | 100
> (1 rows)
>  a  | k | b
> ----+---+-----
>  10 | 1 | 100
> (1 rows)
> -- that view entry's liveness-info is (probably) dead, but the entry is kept alive by
b=100
> DELETE b FROM t WHERE k=1;
> SELECT * from t; SELECT * from mv;
>  k | a    | b
> ---+------+------
>  1 | null | null
> (1 rows)
>  a  | k | b
> ----+---+-----
>  10 | 1 | 100
> (1 rows)
> DELETE FROM t WHERE k=1;
> cqlsh:test> SELECT * from t; SELECT * from mv;
>  k | a | b
> ---+---+---
> (0 rows)
>  a  | k | b
> ----+---+-----
>  10 | 1 | 100
> (1 rows)
> -- deleting the base-entry doesn't help, because the view-key can not be constructed
anymore (a=10 already expired)
> {noformat}
> The problem here is that although the view-entry's liveness-info (probably) expired correctly
a regular column (`b`) keeps the view-entry live. It should have disappeared since it's indexed
column (`a`) expired in the corresponding base-row. This is pretty severe, since that view-entry
is now orphanized.



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