[jira] [Commented] (CASSANDRA-18078) Consider removing MAXWRITETIME function

["Andres de la Peña (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-18078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17640679#comment-17640679 ] 

Andres de la Peña commented on CASSANDRA-18078:
-----------------------------------------------

Here is a patch showing how the removal of {{maxwritetime}} would look like:
||PR||CI||
|[trunk|https://github.com/apache/cassandra/pull/2032]|[j8|https://app.circleci.com/pipelines/github/adelapena/cassandra/2520/workflows/96c76fe9-95d4-4d4d-9a28-2fa8651b7abe] [j11|https://app.circleci.com/pipelines/github/adelapena/cassandra/2520/workflows/e19c0258-cd3c-4864-a103-187a2d0a81de]|

I have preserved the original test cases, even when they are also a bit redundant since we have separate tests for {{writetime}} and {{collection_max}}.

> Consider removing MAXWRITETIME function
> ---------------------------------------
>
>                 Key: CASSANDRA-18078
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-18078
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: CQL/Syntax
>            Reporter: Andres de la Peña
>            Priority: Normal
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> CASSANDRA-17456 added a new {{MAXWRITETIME}} function that allows to retrieve the maximum timestamp of a multi-cell column. For example:
> {code:java}
> > CREATE TABLE t (k int PRIMARY KEY, v set<int>);
> > INSERT INTO t (k, v) VALUES (1, {1, 2}) USING TIMESTAMP 100;
> > UPDATE t USING TIMESTAMP 200 SET v += {3} WHERE k=1;
> > SELECT maxwritetime(v) FROM t;
>  maxwritetime(v)
> -----------------
>              200
> {code}
> Later, CASSANDRA-8877 added the means to retrieve the write times and TTLs of each of the cells in a multi-cell column:
> {code:java}
> > SELECT writetime(v) FROM t;
>  writetime(v)
> -----------------
>  [100, 100, 200]
> > SELECT writetime(v[1]) FROM t;
>  writetime(v[1])
> -----------------
>              100
> {code}
> Quite recently, CASSANDRA-18060 has added generic CQL functions to get the min and max items in a collection. Those functions can be used in combination with the classic {{writetime}} function to get the same results as the new {{maxwritetime}} function:
> {code:java}
> > SELECT collection_max(writetime(v)) FROM t;
>  system.collection_max(writetime(v))
> -------------------------------------
>                                  200
> {code}
> Those new functions can also be used to get the min timestamp, or the min/max TTL, for which there isn't a specific function:
> {code:java}
> SELECT collection_min(writetime(v)) FROM t;
> SELECT collection_min(writetime(v)) FROM t;
> SELECT collection_avg(writetime(v)) FROM t;
> SELECT collection_min(ttl(v)) FROM t;
> SELECT collection_min(ttl(v)) FROM t;
> SELECT collection_avg(ttl(v)) FROM t;
> {code}
> I think this makes the new {{maxwritetime}} mostly redundant, since the new functions can achieve the same results in a more generic way. Since the new {{maxwritetime}} function is only on trunk, we should consider whether we want to remove it in favour of the generic functions.



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