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

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

Andres de la Peña created CASSANDRA-18078:
---------------------------------------------

             Summary: 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


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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