CODEWITHSUNDEEP
cassandracqlcqlengine
Sunil
Sunil

Reputation: 149

Did Update Resulted in UPDATE OR INSERT

Cassandra supports upsert for UPDATE. That is, if the key provided in the update statement doesn't exist in the table; it is implied as insert. Is there a way to know from the return code of the update query if update resulted in update or insert. We would prefer to detect this without an additional read from Cassandra.

We have scenario where we have a very high throughput application where 99% of the events results in insert but a very small chunk results in update. Once updated we would want perform some additional checks and trigger some.

Upvotes: 0

Views: 342

Answers (2)

r005t3r
r005t3r

Reputation: 368

You can add IF EXITS in the end of update statement.

So the update statement would be :

UPDATE person SET name = 'xxxxx' WHERE id = '16843158' IF exists;

for a table person and name, id being the column names.

This would return the True if the row exits and False if not. Using this you can create a check and then "perform some additional checks and trigger some". Also this would not insert anything if row does not exit.

Please check if the true/false is returned as column of Row or as a boolean, because I have checked this in cqlsh only.

Talking for Java. In cqlsh it is displayed as column output.

Upvotes: 3

RussS
RussS

Reputation: 16576

Short answer: All Cassandra writes are upserts, they do not and cannot check the state of the database before writing.

Longer answer: knowing whether a value is set requires a read from Cassandra, meaning that if you want to know whether something exists when you upsert means you end up having to do the anti-pattern of reading before writing.

Basically all data models which require this kind of stateful information will need to take performance penalties. Your best bet is to figure out another way to structure your code. If you really need to know the difference you may try Paxos supported if not exists style requests but know they come at a cost as well.

Upvotes: 1

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