Keyspace and Column Family Storage Configuration¶

name¶

Required. The name for the keyspace.

placement_strategy¶

Required. Determines how replicas for a keyspace will be distributed among nodes in the ring.

Allowed values are:

• org.apache.cassandra.locator.SimpleStrategy
• org.apache.cassandra.locator.NetworkTopologyStrategy
• org.apache.cassandra.locator.OldNetworkTopologyStrategy (deprecated)

These options are described in detail in the replication section.

strategy_options¶

Specifies configuration options for the chosen replication strategy.

For SimpleStrategy, it specifies replication_factor in the format of replication_factor:number_of_replicas.

For NetworkTopologyStrategy, it specifies the number of replicas per data center in a comma separated list of datacenter_name:number_of_replicas. Note that what you specify for datacenter_name depends on the cluster-configured snitch you are using. There is a correlation between the data center name defined in the keyspace strategy_options and the data center name as recognized by the snitch you are using. The nodetool ring command prints out data center names and rack locations of your nodes if you are not sure what they are.

See Choosing Keyspace Replication Options for guidance on how to best configure replication strategy and strategy options for your cluster.

Setting and updating strategy options with the Cassandra CLI requires a slightly different command syntax than other attributes; note the brackets and curly braces in this example:

[default@unknown] CREATE KEYSPACE test
WITH placement_strategy = 'NetworkTopologyStrategy'
AND strategy_options=[{us-east:6,us-west:3}];

column_families¶

A keyspace does not strictly require column families in order to exist as a valid keyspace. In this sense, column families are optional. In a practical sense, most useful keyspaces will contain column families, whose elements are detailed below.

name¶

Required. The user-defined name of the column family.

comparator¶

Defines the data types used to validate and sort column names. There are several built-in column comparators available.

column_type¶

Defaults to Standard for regular column families. For super column families, use Super.

compare_subcolumns_with¶

Required when column_type is “Super”. Same as comparator but for sub-columns of a SuperColumn.

For attributes of columns, see column_metadata.

keys_cached¶

Defines how many key locations will be kept in memory per SSTable (see rows_cached for details on caching actual row values). This can be a fixed number of keys or a fraction (for example 0.5 means 50 percent).

DataStax recommends a fixed sized cache over a relative sized cache. Only use relative cache sizing when you are confident that the data in the column family will not continue to grow over time. Otherwise, your cache will grow as your data set does, potentially causing unplanned memory pressure.

rows_cached¶

Specifies how many rows to cache in memory. This can be a fixed number of rows or a fraction (for example 0.5 means 50 percent).

Using a row cache means that the entire row is cached in memory. This can be detrimental to performance in cases where rows are large, or where rows are frequently modified or removed.

row_cache_provider¶

Specifies the row cache to use for the column family. Allowed values are: * (default) ConcurrentLinkedHashCacheProvider - Rows are cached using the JVM heap, providing the same row cache behavior as Cassandra versions prior to 0.8. * SerializingCacheProvider - Cached rows are serialized and stored in memory off of the JVM heap, which can reduce garbage collection (GC) pressure on the JVM and thereby improve system performance. Serialized rows are also 8-12 times smaller than unserialized rows. This is the recommended setting, as long as you have jna.jar in the CLASSPATH to enable native methods.

comment¶

A human readable comment describing the column family.

read_repair_chance¶

Specifies the probability with which read repairs should be invoked on non-quorum reads. Must be between 0 and 1. Defaults to 1.0 (always perform read repair). Lowering this value will improve throughput, but increase the number of operations that may see stale values if you are not using a strong consistency level.

gc_grace_seconds¶

Specifies the time to wait before garbage collecting tombstones (deletion markers). Defaults to 864000, or 10 days, which allows a great deal of time for consistency to be achieved prior to deletion. In many deployments this interval can be reduced, and in a single-node cluster it can be safely set to zero.

default_validation_class¶

Defines the data type used to validate column values. There are several built-in column validators available.

key_validation_class¶

Defines the data type used to validate row key values. There are several built-in key validators available, however CounterColumnType (distributed counters) cannot be used as a row key validator.

min_compaction_threshold¶

Sets the minimum number of SSTables to trigger a minor compaction. Raising this value causes minor compactions to start less frequently and be more I/O-intensive. Setting this to 0 disables minor compactions. Defaults to 4.

max_compaction_threshold¶

Sets the maximum number of SSTables to allow in a minor compaction. Obsolete now that the compaction_throughput setting has been added.

Setting this to 0 disables minor compactions. Defaults to 32.

row_cache_save_period_in_seconds¶

Sets the number of seconds between saving row caches: the row caches can be saved periodically, and if one exists on startup it will be loaded.

key_cache_save_period_in_seconds¶

Sets number of seconds between saving key caches: the key caches can be saved periodically, and if one exists on startup it will be loaded.

memtable_throughput_in_mb¶

Flush a memtable after this much data has been inserted or updated. Actual heap usage will be greater than this due to overhead from column indexing. This setting must be tuned carefully, as there is (at least) one memtable per column family. See Tuning Java Heap Size for more information on tuning Cassandra memory usage.

memtable_operations_in_millions¶

Like memtable_throughput_in_mb this is per-memtable, but here we define the maximum number of updates that will be allowed to this columnfamily before flushing the memtable. This should be tuned in conjunction with memtable_throughput_in_mb as the first threshold hit will cause a flush. To make tuning easier, Cassandra logs at each flush what the memtable thresholds were.

memtable_flush_after_mins¶

Flush a memtable after this many minutes, even if it is not full yet. Primarily used for making sure infrequently-updated column families do not hold commitlog segments open indefinitely. It should not be the primary threshold hit by a high-traffic column family; that would either cause memory pressure (if the setting is too high) or adversely affect I/O performance (if it is too low).

column_metadata¶

Column metadata defines attributes of a column. Values for name and validation_class are required, though the default_validation_class for the column family is used if no validation_class is specified. Note that index_type must be set to create a secondary index for a column. index_name is not valid unless index_type is also set.

Setting and updating column metadata with the Cassandra CLI requires a slightly different command syntax than other attributes; note the brackets and curly braces in this example:

[default@demo] UPDATE COLUMN FAMILY users WITH comparator=UTF8Type
AND column_metadata=[{column_name: full_name, validation_class: UTF8Type, index_type: KEYS}];