[
https://issues.apache.org/jira/browse/CASSANDRA-14303?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Joseph Lynch updated CASSANDRA-14303:
-------------------------------------
Description:
Right now when creating a keyspace with {{NetworkTopologyStrategy}} the user
has to manually specify the datacenters they want their data replicated to with
parameters, e.g.:
{noformat}
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': 3, 'dc2': 3}{noformat}
This is a poor user interface because it requires the creator of the keyspace
(typically a developer) to know the layout of the Cassandra cluster (which may
or may not be controlled by them). Also, at least in my experience, folks typo
the datacenters _all_ the time. To work around this I see a number of users
creating automation around this where the automation describes the Cassandra
cluster and automatically expands out to all the dcs that Cassandra knows
about. Why can't Cassandra just do this for us, re-using the previously
forbidden {{replication_factor}} option (for backwards compatibility):
{noformat}
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'replication_factor': 3}{noformat}
This would automatically replicate this Keyspace to all datacenters that are
present in the cluster. If you need to _override_ the default you could supply
a datacenter name, e.g.:
{noformat}
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3, 'dc1': 2}
> DESCRIBE KEYSPACE test
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': '2', 'dc2': 3} AND durable_writes = true;
{noformat}
On the implementation side I think this may be reasonably straightforward to do
an auto-expansion at the time of keyspace creation (or alter), where the above
would automatically expand to list out the datacenters. We could allow this to
be recomputed whenever an AlterKeyspaceStatement runs so that to add
datacenters you would just run:
{noformat}
ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'replication_factor': 3}{noformat}
and this would check that if the dc's in the current schema are different you
add in the new ones (_for safety reasons we'd never remove non explicitly
supplied zero dcs when auto-generating dcs_). Removing a datacenter becomes an
alter that includes an override for the dc you want to remove (or of course you
can always not use the auto-expansion and just use the old way):
{noformat}
// Tell it explicitly not to replicate to dc2
> ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3, 'dc2': 0}
> DESCRIBE KEYSPACE test
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': '3'} AND durable_writes = true;{noformat}
was:
Right now when creating a keyspace with {{NetworkTopologyStrategy}} the user
has to manually specify the datacenters they want their data replicated to with
parameters, e.g.:
{noformat}
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': 3, 'dc2': 3}{noformat}
This is a poor user interface because it requires the creator of the keyspace
(typically a developer) to know the layout of the Cassandra cluster (which may
or may not be controlled by them). Also, at least in my experience, folks typo
the datacenters _all_ the time. To work around this I see a number of users
creating automation around this where the automation describes the Cassandra
cluster and automatically expands out to all the dcs that Cassandra knows
about. Why can't Cassandra just do this for us, re-using the previously
forbidden {{replication_factor}} option (for backwards compatibility):
{noformat}
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'replication_factor': 3}{noformat}
This would automatically replicate this Keyspace to all datacenters that are
present in the cluster. If you need to _override_ the default you could supply
a datacenter name, e.g.:
{noformat}
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3, 'dc1': 2}
> DESCRIBE KEYSPACE test
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': '2', 'dc2': 3} AND durable_writes = true;
{noformat}
On the implementation side I think this may be reasonably straightforward to do
an auto-expansion at the time of keyspace creation (or alter), where the above
would automatically expand to list out the datacenters. We could allow this to
be recomputed whenever an AlterKeyspaceStatement runs so that to add
datacenters you would just run:
{noformat}
ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'replication_factor': 3}{noformat}
and this would check that if the dc's in the current schema are different you
add in the new ones (for safety reasons we'd probably never remove non-zero rf
dcs when auto-generating dcs). Removing a datacenter becomes an alter that
includes an override for the dc you want to remove (or of course you can always
not use the auto-expansion and just use the old way):
{noformat}
// Tell it explicitly not to replicate to dc2
> ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3, 'dc2': 0}
> DESCRIBE KEYSPACE test
CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
'dc1': '3'} AND durable_writes = true;{noformat}
> NetworkTopologyStrategy could have a "default replication" option
> -----------------------------------------------------------------
>
> Key: CASSANDRA-14303
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14303
> Project: Cassandra
> Issue Type: Improvement
> Components: Configuration
> Reporter: Joseph Lynch
> Priority: Minor
>
> Right now when creating a keyspace with {{NetworkTopologyStrategy}} the user
> has to manually specify the datacenters they want their data replicated to
> with parameters, e.g.:
> {noformat}
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'dc1': 3, 'dc2': 3}{noformat}
> This is a poor user interface because it requires the creator of the keyspace
> (typically a developer) to know the layout of the Cassandra cluster (which
> may or may not be controlled by them). Also, at least in my experience, folks
> typo the datacenters _all_ the time. To work around this I see a number of
> users creating automation around this where the automation describes the
> Cassandra cluster and automatically expands out to all the dcs that Cassandra
> knows about. Why can't Cassandra just do this for us, re-using the previously
> forbidden {{replication_factor}} option (for backwards compatibility):
> {noformat}
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3}{noformat}
> This would automatically replicate this Keyspace to all datacenters that are
> present in the cluster. If you need to _override_ the default you could
> supply a datacenter name, e.g.:
> {noformat}
> > CREATE KEYSPACE test WITH replication = {'class':
> > 'NetworkTopologyStrategy', 'replication_factor': 3, 'dc1': 2}
> > DESCRIBE KEYSPACE test
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'dc1': '2', 'dc2': 3} AND durable_writes = true;
> {noformat}
> On the implementation side I think this may be reasonably straightforward to
> do an auto-expansion at the time of keyspace creation (or alter), where the
> above would automatically expand to list out the datacenters. We could allow
> this to be recomputed whenever an AlterKeyspaceStatement runs so that to add
> datacenters you would just run:
> {noformat}
> ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'replication_factor': 3}{noformat}
> and this would check that if the dc's in the current schema are different you
> add in the new ones (_for safety reasons we'd never remove non explicitly
> supplied zero dcs when auto-generating dcs_). Removing a datacenter becomes
> an alter that includes an override for the dc you want to remove (or of
> course you can always not use the auto-expansion and just use the old way):
> {noformat}
> // Tell it explicitly not to replicate to dc2
> > ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> > 'replication_factor': 3, 'dc2': 0}
> > DESCRIBE KEYSPACE test
> CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy',
> 'dc1': '3'} AND durable_writes = true;{noformat}
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