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https://issues.apache.org/jira/browse/CASSANDRA-7622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15315709#comment-15315709
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Jeff Jirsa commented on CASSANDRA-7622:
---------------------------------------
Proposing:
{code}
CREATE TABLE
USING 'o.a.c.db.virtual.ClassName'
[IF NOT EXISTS]
ks.cfName ( column text, column2 int, etc )
WITH virtual_table_options = {'key':'value', 'key2':'value2'}
{code}
Implication here is that K_USING already exists in the grammar (e.g. custom
indexes), and it's fairly consistent for users. Presence of {{USING class}}
would sets a {{VIRTUAL}} flag for the CFMetaData. Instantiate the specified
class passing the CFMetadata and key/value map, store the resulting instance
somewhere (map within Schema?). Columns would still be defined in the standard
way, persisted to the normal schema tables so drivers / cqlsh wouldn't need to
be modified.
At minimum, the virtual tables should implement:
{code}
public String class();
public Map<String,String> options();
public String keyspace();
public String tableName();
public boolean writable();
public void execute(PartitionUpdate update, Clustering clustering,
UpdateParameters params) throws InvalidRequestException;
public boolean readable();
public ResultMessage.Rows execute(QueryState state, QueryOptions options)
throws RequestExecutionException, RequestValidationException;
{code}
Then, in {{SelectStatement}} if the CFMetadata isVirtual and {{readable()}},
pass state/options from {{SelectStatement.execute}} through to the virtual
table's version.
Similarly, in {{UpdateStatement}}, if CFMetadata isVirtual for any updated rows
and {{writable()}}, pass partitionKey + params from {{UpdataStatement.execute}}
through to the virtual table's version.
The virtual tables I'm specifically interested in:
- JMX getters and setters, probably implemented as multiple smaller virtual
tables:
-- Ring state / equivalent of {{nodetool gossipinfo}} / {{o.a.c.net
FailureDetector}}
-- CF attributes / equivalent of {{o.a.c.db ColumnFamilies.keyspace.table
CompactionParametersJson}} and similar
-- JMX {{o.a.c.metrics}}
- YAML config getters and setters a la CASSANDRA-9233
- SSTableMetadata virtual table (list all sstables per CF, showing timestamps /
repairedAt, ponies may with UPDATE .. SET deleted=true to mark a table obsolete)
Feedback appreciated on all of this, but especially:
- The two meaty {{execute}} functions here provide a lot of flexibility, but
also a lot of rope - is it too much rope?
- On {{ALTER}} table: we could simply replace the instance in the map, or do we
disallow ALTER (and instead require DROP + CREATE)?
> Implement virtual tables
> ------------------------
>
> Key: CASSANDRA-7622
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7622
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Tupshin Harper
> Assignee: Jeff Jirsa
> Fix For: 3.x
>
>
> There are a variety of reasons to want virtual tables, which would be any
> table that would be backed by an API, rather than data explicitly managed and
> stored as sstables.
> One possible use case would be to expose JMX data through CQL as a
> resurrection of CASSANDRA-3527.
> Another is a more general framework to implement the ability to expose yaml
> configuration information. So it would be an alternate approach to
> CASSANDRA-7370.
> A possible implementation would be in terms of CASSANDRA-7443, but I am not
> presupposing.
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