It is not (yet) possible to use functions in LWT predicates. LWT only
supports = and != plus IF (NOT) EXISTS right now
Le 11 mai 2016 16:50, "Bhuvan Rawal" <bhu1ra...@gmail.com> a écrit :
> Hi,
>
> I was working on maintaining counters in cassandra, I read that it is not
> 100% accurate, I have tested them to be extremely accurate with 3.0.5 but
> going by docs there may be slight in accuracy.
>
> Thinking about this I thought there may be 2 approaches to resolve this:
> 1. Read the existing count and write the new count if table count is the
> count earlier fetched using LWT transaction.
> 2. Read the existing writetime(count) and write the new count if
> writetime(count) is the writetime count earlier fetched using lightweight
> transaction.-
>
> For me approach1 is working, but approach 2 doesnt. Please Find below the
> same:
>
> superuser@cqlsh:test_keyspace> CREATE TABLE test_keyspace.test (
> ... part_k int,
> ... clust_k text,
> ... count int,
> ... PRIMARY KEY (part_k, clust_k)
> ... );
> superuser@cqlsh:test_keyspace> insert into test(part_k , clust_k , count )
> values (2390, 'Test Ck Value', 007);
> superuser@cqlsh:test_keyspace> select * from test;
>
> part_k | clust_k | count
> --------+---------------+-------
> 2390 | Test Ck Value | 7
>
> superuser@cqlsh:test_keyspace> update test set count=8 where part_k=2390
> and clust_k='Test Ck Value' if count=7;
> # Works perfectly
>
> superuser@cqlsh:test_keyspace> select
> writetime(count),part_k,clust_k,count
> from test;
>
> writetime(count) | part_k | clust_k | count
> ------------------+--------+---------------+-------
> 1462974475292000 | 2390 | Test Ck Value | 8
>
> # Now try to use the write time in LWT
> superuser@cqlsh:test_keyspace> update test set count=8 where part_k=2390
> and clust_k='Test Ck Value' if writetime(count)=1462974475292000;
> SyntaxException: <ErrorMessage code=2000 [Syntax error in CQL query]
> message="line 1:82 no viable alternative at input '(' (... and
> clust_k='Test Ck Value' if writetime[(]...)">
>
> Best Regards,
> Bhuvan Rawal
>
