I have a table in Cassandra which gets updated all the time. I wanted to know, if the write time of a row / value gets updated with each update to the data in the row or if there is only one write time (timestamp) given when i first write to the table that never changes. Thanks to anyone who can answer :)
2 Answers
Here is an example showing that the timestamp changes only on the column updated:
cqlsh:keyspace1> create table keyspace1.testwrites (id int primary key, firstname text, lastname text);
cqlsh:keyspace1> insert into testwrites(id, firstname, lastname) values (1, 'Valerie', 'Rodriguez');
cqlsh:keyspace1> select id, firstname, writetime(firstname), lastname, writetime(lastname) from testwrites;
id | firstname | writetime(firstname) | lastname | writetime(lastname)
----+-----------+----------------------+-----------+---------------------
1 | Valerie | 1561471068014970 | Rodriguez | 1561471068014970
(1 rows)
cqlsh:keyspace1> insert into testwrites(id, firstname, lastname) values (2, 'Valerie', 'Smith');
cqlsh:keyspace1> select id, firstname, writetime(firstname), lastname, writetime(lastname) from testwrites;
id | firstname | writetime(firstname) | lastname | writetime(lastname)
----+-----------+----------------------+-----------+---------------------
1 | Valerie | 1561471068014970 | Rodriguez | 1561471068014970
2 | Valerie | 1561471078606684 | Smith | 1561471078606684
(2 rows)
cqlsh:keyspace1> insert into testwrites(id, firstname, lastname) values (2, 'Valerie', 'Jones');
cqlsh:keyspace1> select id, firstname, writetime(firstname), lastname, writetime(lastname) from testwrites;
id | firstname | writetime(firstname) | lastname | writetime(lastname)
----+-----------+----------------------+-----------+---------------------
1 | Valerie | 1561471068014970 | Rodriguez | 1561471068014970
2 | Valerie | 1561471097668583 | Jones | 1561471097668583
(2 rows)
cqlsh:keyspace1> insert into testwrites(id, firstname, lastname) values (3, 'Valerie', 'Garcia');
cqlsh:keyspace1> select id, firstname, writetime(firstname), lastname, writetime(lastname) from testwrites;
id | firstname | writetime(firstname) | lastname | writetime(lastname)
----+-----------+----------------------+-----------+---------------------
1 | Valerie | 1561471068014970 | Rodriguez | 1561471068014970
2 | Valerie | 1561471097668583 | Jones | 1561471097668583
3 | Valerie | 1561471114925083 | Garcia | 1561471114925083
(3 rows)
cqlsh:keyspace1> update testwrites set firstname='Alex' where id=1;
cqlsh:keyspace1> select id, firstname, writetime(firstname), lastname, writetime(lastname) from testwrites;
id | firstname | writetime(firstname) | lastname | writetime(lastname)
----+-----------+----------------------+-----------+---------------------
1 | Alex | 1561471131764488 | Rodriguez | 1561471068014970
2 | Valerie | 1561471097668583 | Jones | 1561471097668583
3 | Valerie | 1561471114925083 | Garcia | 1561471114925083
Since the data is written at each update, write time will update with each update as well.
Also, write time is for a column, WRITETIME function also takes the column to retrieve the timestamp.
Refer to documentation here
Related