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https://issues.apache.org/jira/browse/CASSANDRA-16737?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17370787#comment-17370787
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Ekaterina Dimitrova edited comment on CASSANDRA-16737 at 6/28/21, 6:41 PM:
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I wanted to help here so I will take a look but [~jlewandowski] -and-
[~adelapena] might also want to look at it as they were reviewing the previous
ticket. Also, I am going on vacation on Wednesday so no need to be pending on
me in case we don't finish working on it async tomorrow.
EDIT: It was [~maedhroz] reviewing the previous one, [~jlewandowski] and
[~adelapena] looked at a different one, my bad.
was (Author: e.dimitrova):
I wanted to help here so I will take a look but [~jlewandowski] and
[~adelapena] might also want to look at it as they were reviewing the previous
ticket. Also, I am going on vacation on Wednesday so no need to be pending on
me in case we don't finish working on it async tomorrow.
> 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: 20m
> Remaining Estimate: 0h
>
> With the following SSTables:
> {code}
> 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}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.
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