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From "ZhaoYang (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-13127) Materialized Views: View row expires too soon
Date Mon, 10 Jul 2017 05:08:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13127?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16079873#comment-16079873
] 

ZhaoYang edited comment on CASSANDRA-13127 at 7/10/17 5:07 AM:
---------------------------------------------------------------

[~tjake]  yes, it will have to read existing data more often. 

the extra cases are:  when updating base's columns which are not used in view.  If a user
has multiple views on a base, read-before-write is very likely to happen, the original optimization
won't help too much.

another naive way is to ignore the TTL effect on view in the given example or totally disable
TTL on table with MV. because it may not make sense to denormalize a short-life data..




was (Author: jasonstack):
[~tjake]  yes, it will have to read existing data more often. 

the extra cases are:  when updating base's columns which are not used in view.  If a user
has multiple views on a base, read-before-write is very likely to happen, the original optimization
won't help too much.

another naive way is totally disable TTL on table with MV. because it may not make sense to
denormalize a short-life data..



> Materialized Views: View row expires too soon
> ---------------------------------------------
>
>                 Key: CASSANDRA-13127
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13127
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Local Write-Read Paths, Materialized Views
>            Reporter: Duarte Nunes
>            Assignee: ZhaoYang
>
> Consider the following commands, ran against trunk:
> {code}
> echo "DROP MATERIALIZED VIEW ks.mv; DROP TABLE ks.base;" | bin/cqlsh
> echo "CREATE TABLE ks.base (p int, c int, v int, PRIMARY KEY (p, c));" | bin/cqlsh
> echo "CREATE MATERIALIZED VIEW ks.mv AS SELECT p, c FROM base WHERE p IS NOT NULL AND
c IS NOT NULL PRIMARY KEY (c, p);" | bin/cqlsh
> echo "INSERT INTO ks.base (p, c) VALUES (0, 0) USING TTL 10;" | bin/cqlsh
> # wait for row liveness to get closer to expiration
> sleep 6;
> echo "UPDATE ks.base USING TTL 8 SET v = 0 WHERE p = 0 and c = 0;" | bin/cqlsh
> echo "SELECT p, c, ttl(v) FROM ks.base; SELECT * FROM ks.mv;" | bin/cqlsh
>  p | c | ttl(v)
> ---+---+--------
>  0 | 0 |      7
> (1 rows)
>  c | p
> ---+---
>  0 | 0
> (1 rows)
> # wait for row liveness to expire
> sleep 4;
> echo "SELECT p, c, ttl(v) FROM ks.base; SELECT * FROM ks.mv;" | bin/cqlsh
>  p | c | ttl(v)
> ---+---+--------
>  0 | 0 |      3
> (1 rows)
>  c | p
> ---+---
> (0 rows)
> {code}
> Notice how the view row is removed even though the base row is still live. I would say
this is because in ViewUpdateGenerator#computeLivenessInfoForEntry the TTLs are compared instead
of the expiration times, but I'm not sure I'm getting that far ahead in the code when updating
a column that's not in the view.



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