CONSISTENCY
Determines how many nodes in the replica must respond for the coordinator node to successfully process a non-lightweight transaction during the CQL shell session.
Consistency level determines how many nodes in the replica must respond for the coordinator node to successfully process a non-lightweight transaction.
IF EXISTS
or IF NOT EXISTS
, using SERIAL CONSISTENCY.Synopsis
CONSISTENCY [level]
Syntax conventions | Description |
---|---|
UPPERCASE | Literal keyword. |
Lowercase | Not literal. |
Italics |
Variable value. Replace with a user-defined value. |
[] |
Optional. Square brackets ( [] ) surround optional command
arguments. Do not type the square brackets. |
( ) |
Group. Parentheses ( ( ) ) identify a group to choose from. Do
not type the parentheses. |
| |
Or. A vertical bar ( | ) separates alternative elements. Type
any one of the elements. Do not type the vertical bar. |
... |
Repeatable. An ellipsis ( ... ) indicates that you can repeat
the syntax element as often as required. |
'Literal string' |
Single quotation ( ' ) marks must surround literal strings in
CQL statements. Use single quotation marks to preserve upper case. |
{ key : value } |
Map collection. Braces ( { } ) enclose map collections or key
value pairs. A colon separates the key and the value. |
<datatype1,datatype2> |
Set, list, map, or tuple. Angle brackets ( < > ) enclose
data types in a set, list, map, or tuple. Separate the data types with a comma.
|
cql_statement; |
End CQL statement. A semicolon ( ; ) terminates all CQL
statements. |
[--] |
Separate the command line options from the command arguments with two hyphens (
-- ). This syntax is useful when arguments might be mistaken for
command line options. |
' <schema> ... </schema> ' |
Search CQL only: Single quotation marks ( ' ) surround an
entire XML schema declaration. |
@xml_entity='xml_entity_type' |
Search CQL only: Identify the entity and literal value to overwrite the XML element in the schema and solrConfig files. |
Displaying the current level
CONSISTENCY
Current consistency level is ONE.
The default CQL shell level is ONE
.
Setting a level
Level determines data availability versus data accuracy for transactions during the CQL shell session, some settings also may have high impact other transactions occurring in the cluster, such as ALL and SERIAL. The CQL shell setting supersedes Cassandra consistency level global setting.
When you initiate a transaction from the CQL shell, the coordinator node is typically the node where you started cqlsh; if you connect to a remote host, then the remote node is the coordinator.
Level | Replicas | Consistency | Availability |
---|---|---|---|
ALL |
All | Highest | Lowest |
EACH_QUORUM |
Quorum in each data centers. Reads NOT supported. |
Same across data centers | |
QUORUM |
Quorum of all nodes across all data centers. Some level of failure. | ||
LOCAL_QUORUM |
Quorum of replicas in the same data center as the coordinator. Avoids latency of inter-datacenter communication. | Low in multi-data center | |
ONE |
Closest replica as determined by the snitch. Satisfies the needs of most users because consistency requirements are not stringent. | Lowest (READ) | Highest (READ) |
TWO |
Closest two replicas as determined by the snitch. | ||
THREE |
Closest three replicas as determined by the snitch. | ||
LOCAL_ONE |
Returns a response from the closest replica in the local data center. For security and quality, use in an off line datacenter to prevent automatic connection to online nodes in other datacenters. | ||
ANY | Closest replica, as determined by the snitch. If all replica nodes are down, write succeeds after a hinted handoff. Provides low latency, guarantees writes never fail. |
Lowest (WRITE) | Highest (WRITE) |
SERIAL |
Returns results with the most recent data including inflight LWT (uncommitted). Commits inflight LWT as part
of the read. Writes NOT supported. |
||
LOCAL_SERIAL |
Same as SERIAL , but confined to the data center. Writes NOT supported. |
Examples
Set CONSISTENCY
to force the majority of the nodes to respond:
CONSISTENCY QUORUM
Set level to serial for LWT read requests:
CONSISTENCY SERIAL
Consistency level set to SERIAL.
SELECT * FROM cycling.race_winners ;
@ Row 1
---------------+--------------------------------------------------
race_name | National Championships South Africa WJ-ITT (CN)
race_position | 1
cyclist_name | {firstname: 'Frances', lastname: 'DU TOUT'}
@ Row 2
---------------+--------------------------------------------------
race_name | National Championships South Africa WJ-ITT (CN)
race_position | 2
cyclist_name | {firstname: 'Lynette', lastname: 'BENSON'}
@ Row 3
---------------+--------------------------------------------------
race_name | National Championships South Africa WJ-ITT (CN)
race_position | 3
cyclist_name | {firstname: 'Anja', lastname: 'GERBER'}
@ Row 4
---------------+--------------------------------------------------
race_name | National Championships South Africa WJ-ITT (CN)
race_position | 4
cyclist_name | {firstname: 'Ame', lastname: 'VENTER'}
@ Row 5
---------------+--------------------------------------------------
race_name | National Championships South Africa WJ-ITT (CN)
race_position | 5
cyclist_name | {firstname: 'Danielle', lastname: 'VAN NIEKERK'}
(5 rows)
expand ON
for legibility.Inserts with CONSISTENCY SERIAL fail:
INSERT INTO cycling.race_winners ( race_name , race_position , cyclist_name ) VALUES ( 'National Championships South Africa WJ-ITT (CN)' , 7 , { firstname: 'Joe' , lastname: 'Anderson' } ) IF NOT EXISTS ;
InvalidRequest: Error from server: code=2200 [Invalid query] message="LOCAL_SERIAL is not supported as conditional update commit consistency. Use ANY if you mean "make sure it is accepted but I don't care how many replicas commit it for non-SERIAL reads""
Updates with CONSISTENCY SERIAL also fail:
UPDATE cycling.race_winners SET cyclist_name = { firstname: 'JOHN' , lastname: 'DOE' } WHERE race_name='National Championships South Africa WJ-ITT (CN)' AND race_position = 6 IF EXISTS ;
InvalidRequest: Error from server: code=2200 [Invalid query] message="LOCAL_SERIAL is not supported as conditional update commit consistency. Use ANY if you mean "make sure it is accepted but I don't care how many replicas commit it for non-SERIAL reads""