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https://issues.apache.org/jira/browse/CASSANDRA-6412?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jeff Jirsa updated CASSANDRA-6412:
----------------------------------
Comment: was deleted
(was: I'm playing with this, just to understand it conceptually, using
CASSANDRA-8099 as a base.
{noformat}
cqlsh> create keyspace test2 WITH replication = {'class': 'SimpleStrategy',
'replication_factor': 2}; use test2;
cqlsh:test2> select column_name, column_resolver from system.schema_columns
where keyspace_name='test2' and columnfamily_name='table_with_resolvers';
column_name | column_resolver
-------------+------------------------------------------------------------
first | org.apache.cassandra.db.resolvers.ReverseTimestampResolver
high | org.apache.cassandra.db.resolvers.MaxValueResolver
id | org.apache.cassandra.db.resolvers.TimestampResolver
last | org.apache.cassandra.db.resolvers.TimestampResolver
low | org.apache.cassandra.db.resolvers.MinValueResolver
(5 rows)
cqlsh:test2> create table table_with_resolvers ( id text, low int with resolver
'org.apache.cassandra.db.resolvers.MinValueResolver', high int with resolver
'org.apache.cassandra.db.resolvers.MaxValueResolver', last int with resolver
'org.apache.cassandra.db.resolvers.TimestampResolver', first int with resolver
'org.apache.cassandra.db.resolvers.ReverseTimestampResolver', PRIMARY KEY(id));
cqlsh:test2> insert into table_with_resolvers (id, low, high, first, last )
values ('1', 1, 1, 1, 1);
cqlsh:test2> insert into table_with_resolvers (id, low, high, first, last )
values ('1', 2, 2, 2, 2);
cqlsh:test2> insert into table_with_resolvers (id, low, high, first, last )
values ('1', 3, 3, 3, 3);
cqlsh:test2> insert into table_with_resolvers (id, low, high, first, last )
values ('1', 5, 5, 5, 5);
cqlsh:test2> insert into table_with_resolvers (id, low, high, first, last )
values ('1', 4, 4, 4, 4);
cqlsh:test2> select * from table_with_resolvers;
id | first | high | last | low
----+-------+------+------+-----
1 | 1 | 5 | 4 | 1
(1 rows)
{noformat}
My diff/patch isn't fit for sharing at this time but as I'm going through, I
had some questions:
1) Given that user types are frozen, does it make sense to allow a resolver per
field in user types, assuming that eventually user types will become un-frozen?
2) My initial pass disallows custom resolvers on counters and collections -
does anyone have any strong opinion on whether or not user defined merge
functions should be allowed for collections?
3) Still battling through deletion/tombstone reconciliation. Still making sure
I fully understand all of the problem cases. )
> Custom creation and merge functions for user-defined column types
> -----------------------------------------------------------------
>
> Key: CASSANDRA-6412
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6412
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Nicolas Favre-Felix
>
> This is a proposal for a new feature, mapping custom types to Cassandra
> columns.
> These types would provide a creation function and a merge function, to be
> implemented in Java by the user.
> This feature relates to the concept of CRDTs; the proposal is to replicate
> "operations" on these types during write, to apply these operations
> internally during merge (Column.reconcile), and to also merge their values on
> read.
> The following operations are made possible without reading back any data:
> * MIN or MAX(value) for a column
> * First value for a column
> * Count Distinct
> * HyperLogLog
> * Count-Min
> And any composition of these too, e.g. a Candlestick type includes first,
> last, min, and max.
> The merge operations exposed by these types need to be commutative; this is
> the case for many functions used in analytics.
> This feature is incomplete without some integration with CASSANDRA-4775
> (Counters 2.0) which provides a Read-Modify-Write implementation for
> distributed counters. Integrating custom creation and merge functions with
> new counters would let users implement complex CRDTs in Cassandra, including:
> * Averages & related (sum of squares, standard deviation)
> * Graphs
> * Sets
> * Custom registers (even with vector clocks)
> I have a working prototype with implementations for min, max, and Candlestick
> at https://github.com/acunu/cassandra/tree/crdts - I'd appreciate any
> feedback on the design and interfaces.
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