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https://issues.apache.org/jira/browse/CASSANDRA-6870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13937029#comment-13937029
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Edward Capriolo commented on CASSANDRA-6870:
--------------------------------------------
https://github.com/edwardcapriolo/cassandra/compare/arizona?expand=1
CQLwise this function could look something like this:
{quote}
update table set col1=increment(col1) where rowkey = 5;
{quote}
Thrift world it looks like this:
{quote}
struct TransformRequest {
1: optional binary key,
2: optional string column_family,
3: optional string function_name,
4: optional map<binary,binary> function_properties
5: optional cassandra.ConsistencyLevel
serial_consistency_level=cassandra.ConsistencyLevel.SERIAL,
6: optional cassandra.ConsistencyLevel
commit_consistency_level=cassandra.ConsistencyLevel.QUORUM,
7: optional cassandra.SlicePredicate predicate
}
{quote}
Given an interface like this:
{code}
public interface Transformer {
public ColumnFamily transform(ColumnFamily source, Map<String,String>
properties, CFMetaData cfm);
}
{code}
We can perform an increment.
{code}
public class Increment implements Transformer {
@Override
public ColumnFamily transform(ColumnFamily source, Map<String, String>
properties, CFMetaData cfm) {
ColumnFamily updates = ArrayBackedSortedColumns.factory.create(cfm);
if (source == null){
return updates;
}
for (Cell cell : source.getSortedColumns()) {
CellName cn = CellNames.simpleDense(cell.name().get(0));
int newValue = 0;
try {
newValue = Integer.parseInt(ByteBufferUtil.string(cell.value())) +1;
} catch (NumberFormatException | CharacterCodingException e) {
e.printStackTrace();
return updates;
}
updates.addColumn(cn, ByteBufferUtil.bytes(newValue+""),
FBUtilities.timestampMicros());
}
return updates;
}
}
{code}
I have this working in my branch. By working I mean compiling and test passing.
(I am fuzzy on paxos so I am not sure if this is implemented correctly). This
concept is powerful, increment, append, operations on collections could be
possible.
> Transform operation
> -------------------
>
> Key: CASSANDRA-6870
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6870
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Edward Capriolo
> Assignee: Edward Capriolo
> Priority: Minor
>
> Compare and swap uses paxos to only update a value only if some criteria is
> met. If I understand correctly we should be able to use this feature to
> provide a wider variety of server side operations.
> For example inside a paxos transaction performing a slice and then using a
> function to manipulate the slice. You could accomplish features like append
> and increment this way.
> I took a stab at doing this. I **think** I did it correctly. Comments welcome.
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