Overview
The Cassandra Thrift API changed between 0.3, 0.4, 0.5 and 0.6; this document explains the 0.6 version.
Cassandra's client API is built entirely on top of Thrift. It should be noted that these documents mention default values, but these are not generated in all of the languages that Thrift supports. Full examples of using Cassandra from Thrift, including setup boilerplate, are found on ThriftExamples. Higher-level clients are linked from ClientOptions.
WARNING: Some SQL/RDBMS terms are used in this documentation for analogy purposes. They should be thought of as just that; analogies. There are few similarities between how data is managed in a traditional RDBMS and Cassandra. Please see DataModel for more information.
Terminology / Abbreviations
Keyspace
CF
SCF
Key
Column
Exceptions
NotFoundException
InvalidRequestException
UnavailableException
TimedOutException
TApplicationException
AuthenticationException
AuthorizationException
Structures
ConsistencyLevel
The ConsistencyLevel
is an enum
that controls both read and write behavior based on <ReplicationFactor>
in your storage-conf.xml
. The different consistency levels have different meanings, depending on if you're doing a write or read operation. Note that if W
+ R
> ReplicationFactor
, where W is the number of nodes to block for on write, and R the number to block for on reads, you will have strongly consistent behavior; that is, readers will always see the most recent write. Of these, the most interesting is to do QUORUM
reads and writes, which gives you consistency while still allowing availability in the face of node failures up to half of ReplicationFactor
. Of course if latency is more important than consistency then you can use lower values for either or both.
All discussion of "nodes" here refers to nodes responsible for holding data for the given key; "surrogate" nodes involved in HintedHandoff do not count towards achieving the requested ConsistencyLevel.
Write
Level |
Behavior |
|
Ensure nothing. A write happens asynchronously in background |
|
Ensure that the write has been written to at least 1 node, including hinted recipients. |
|
Ensure that the write has been written to at least 1 node's commit log and memory table before responding to the client. |
|
Ensure that the write has been written to |
|
Ensure that the write is written to all |
Read
Level |
Behavior |
|
Not supported, because it doesn't make sense. |
|
Not supported. You probably want ONE instead. |
|
Will return the record returned by the first node to respond. A consistency check is always done in a background thread to fix any consistency issues when |
|
Will query all nodes and return the record with the most recent timestamp once it has at least a majority of replicas reported. Again, the remaining replicas will be checked in the background. |
|
Will query all nodes and return the record with the most recent timestamp once all nodes have replied. Any unresponsive nodes will fail the operation. |
Note: Different language toolkits may have their own Consistency Level defaults as well. To ensure the desired Consistency Level, you should always explicitly set the Consistency Level.
ColumnOrSuperColumn
Due to the lack of inheritance in Thrift, Column
and SuperColumn
structures are aggregated by the ColumnOrSuperColumn
structure. This is used wherever either a Column
or SuperColumn
would normally be expected.
If the underlying column is a Column
, it will be contained within the column
attribute. If the underlying column is a SuperColumn
, it will be contained within the super_column
attribute. The two are mutually exclusive - i.e. only one may be populated.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
N |
The |
|
|
n/a |
N |
The |
Column
The Column
is a triplet of a name, value and timestamp. As described above, Column
names are unique within a row. Timestamps are arbitrary - they can be any integer you specify, however they must be consistent across your application. It is recommended to use a timestamp value with a fine granularity, such as microseconds since the UNIX epoch. See DataModel for more information.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The name of the |
|
|
n/a |
Y |
The value of the |
|
|
n/a |
Y |
The timestamp of the |
SuperColumn
A SuperColumn
contains no data itself, but instead stores another level of Columns
below the key. See DataModel for more details on what SuperColumns
are and how they should be used.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The name of the |
|
|
n/a |
Y |
The |
ColumnPath
The ColumnPath
is the path to a single column in Cassandra. It might make sense to think of ColumnPath
and ColumnParent
in terms of a directory structure.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The name of the CF of the column being looked up. |
|
|
n/a |
N |
The super column name. |
|
|
n/a |
N |
The column name. |
ColumnParent
The ColumnParent
is the path to the parent of a particular set of Columns
. It is used when selecting groups of columns from the same ColumnFamily. In directory structure terms, imagine ColumnParent
as ColumnPath + '/../'
.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The name of the CF of the column being looked up. |
|
|
n/a |
N |
The super column name. |
SlicePredicate
A SlicePredicate
is similar to a mathematic predicate, which is described as "a property that the elements of a set have in common."
SlicePredicate
's in Cassandra are described with either a list of column_names
or a SliceRange
.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
N |
A list of column names to retrieve. This can be used similar to Memcached's "multi-get" feature to fetch N known column names. For instance, if you know you wish to fetch columns 'Joe', 'Jack', and 'Jim' you can pass those column names as a list to fetch all three at once. |
|
|
n/a |
N |
A |
If column_names
is specified, slice_range
is ignored.
SliceRange
A SliceRange
is a structure that stores basic range, ordering and limit information for a query that will return multiple columns. It could be thought of as Cassandra's version of LIMIT
and ORDER BY
.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The column name to start the slice with. This attribute is not required, though there is no default value, and can be safely set to |
|
|
n/a |
Y |
The column name to stop the slice at. This attribute is not required, though there is no default value, and can be safely set to an empty byte array to not stop until |
|
|
|
Y |
Whether the results should be ordered in reversed order. Similar to |
|
|
|
Y |
How many columns to return. Similar to |
KeyRange
A KeyRange
is used by get_range_slices
to define the range of keys to get the slices for.
The semantics of start keys and tokens are slightly different. Keys are start-inclusive; tokens are start-exclusive. Token ranges may also wrap – that is, the end token may be less than the start one. Thus, a range from keyX to keyX is a one-element range, but a range from tokenY to tokenY is the full ring.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
N |
The first key in the inclusive |
|
|
n/a |
N |
The last key in the inclusive |
|
|
n/a |
N |
The first token in the exclusive |
|
|
n/a |
N |
The last token in the exclusive |
|
|
100 |
Y |
The total number of keys to permit in the |
KeySlice
A KeySlice
encapsulates a mapping of a key to the slice of columns for it as returned by the get_range_slices operation. Normally, when slicing a single key, a list<ColumnOrSuperColumn>
of the slice would be returned. When slicing multiple or a range of keys, a list<KeySlice>
is instead returned so that each slice can be mapped to their key.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The key for the slice. |
|
|
n/a |
Y |
The columns in the slice. |
TokenRange
A structure representing structural information about the cluster provided by the describe
utility methods detailed below.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The first token in the |
|
|
n/a |
Y |
The last token in the |
|
|
n/a |
Y |
A list of the endpoints (nodes) that replicate data in the |
Mutation
A Mutation
encapsulates either a column to insert, or a deletion to execute for a key. Like ColumnOrSuperColumn
, the two properties are mutually exclusive - you may only set one on a Mutation.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
N |
The column to insert in to the key. |
|
|
n/a |
N |
The deletion to execute on the key. |
Deletion
A Deletion
encapsulates an operation that will delete all columns matching the specified timestamp
and predicate
. If super_column
is specified, the Deletion
will operate on columns within the SuperColumn
- otherwise it will operate on columns in the top-level of the key.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
The timestamp of the column(s) to be deleted. |
|
|
n/a |
N |
The super column to delete the column(s) from. |
|
|
n/a |
N |
A predicate to match the column(s) to be deleted from the key/super column. |
AuthenticationRequest
A structure that encapsulates a request for the connection to be authenticated. The authentication credentials are arbitrary - this structure simply provides a mapping of credential name to credential value.
Attribute |
Type |
Default |
Required |
Description |
|
|
n/a |
Y |
A map of named credentials. |
Method calls
login
void login(keyspace, auth_request)
Authenticates with the cluster for operations on the specified keyspace using the specified AuthenticationRequest
credentials. Throws AuthenticationException
if the credentials are invalid or AuthorizationException
if the credentials are valid, but not for the specified keyspace.
get
ColumnOrSuperColumn get(keyspace, key, column_path, consistency_level)
Get the Column
or SuperColumn
at the given column_path
. If no value is present, NotFoundException
is thrown. (This is the only method that can throw an exception under non-failure conditions.)
get_slice
list<ColumnOrSuperColumn> get_slice(keyspace, key, column_parent, predicate, consistency_level)
Get the group of columns contained by column_parent
(either a ColumnFamily
name or a ColumnFamily/SuperColumn
name pair) specified by the given SlicePredicate
struct.
multiget_slice
map<string,list<ColumnOrSuperColumn>> multiget_slice(keyspace, keys, column_parent, predicate, consistency_level)
Retrieves slices for column_parent
and predicate
on each of the given keys in parallel. Keys are a `list<string> of the keys to get slices for.
This is similar to get_range_slice
(Cassandra 0.5) except operating on a set of non-contiguous keys instead of a range of keys.
get_count
i32 get_count(keyspace, key, column_parent, consistency_level)
Counts the columns present in column_parent
.
The method is not O(1). It takes all the columns from disk to calculate the answer. The only benefit of the method is that you do not need to pull all the columns over Thrift interface to count them.
get_range_slices
list<KeySlice> get_range_slices(keyspace, column_parent, predicate, range, consistency_level)
Replaces get_range_slice
. Returns a list of slices for the keys within the specified KeyRange
. Unlike get_key_range, this applies the given predicate to all keys in the range, not just those with undeleted matching data. This method is only allowed when using an order-preserving partitioner.
insert
insert(keyspace, key, column_path, value, timestamp, consistency_level)
Insert a Column
consisting of (column_path.column
, value
, timestamp
) at the given column_path.column_family
and optional column_path.super_column
. Note that column_path.column
is here required, since a SuperColumn cannot directly contain binary values – it can only contain sub-Columns.
batch_mutate
batch_mutate(keyspace, mutation_map, consistency_level)
Executes the specified mutations on the keyspace. mutation_map
is a map<string, map<string, list<Mutation>>>
; the outer map maps the key to the inner map, which maps the column family to the Mutation
; can be read as: map<key : string, map<column_family : string, list<Mutation>>>
. To be more specific, the outer map key is a row key, the inner map key is the column family name.
A Mutation
specifies either columns to insert or columns to delete. See Mutation
and Deletion
above for more details.
remove
remove(keyspace, key, column_path, timestamp, consistency_level)
Remove data from the row specified by key
at the granularity specified by column_path
, and the given timestamp
. Note that all the values in column_path
besides column_path.column_family
are truly optional: you can remove the entire row by just specifying the ColumnFamily, or you can remove a SuperColumn or a single Column by specifying those levels too. Note that the timestamp
is needed, so that if the commands are replayed in a different order on different nodes, the same result is produced.
describe_keyspaces
set<string> describe_keyspaces()
Gets a list of all the keyspaces configured for the cluster.
describe_cluster_name
string describe_cluster_name()
Gets the name of the cluster.
describe_version
string describe_version()
Gets the Thrift API version.
describe_ring
list<TokenRange> describe_ring(keyspace)
Gets the token ring; a map of ranges to host addresses. Represented as a set of TokenRange
instead of a map from range to list of endpoints, because you can't use Thrift structs as map keys: https://issues.apache.org/jira/browse/THRIFT-162 for the same reason, we can't return a set here, even though order is neither important nor predictable.
describe_keyspace
map<string, map<string, string>> describe_keyspace(keyspace)
Gets information about the specified keyspace.