Net::Async::CassandraCQL - use Cassandra databases with IO::Async using CQL
Net::Async::CassandraCQL
use IO::Async::Loop; use Net::Async::CassandraCQL; use Protocol::CassandraCQL qw( CONSISTENCY_QUORUM ); my $loop = IO::Async::Loop->new; my $cass = Net::Async::CassandraCQL->new( host => "localhost", keyspace => "my-keyspace", default_consistency => CONSISTENCY_QUORUM, ); $loop->add( $cass ); $cass->connect->get; my @f; foreach my $number ( 1 .. 100 ) { push @f, $cass->query( "INSERT INTO numbers (v) VALUES $number" ); } Future->needs_all( @f )->get; my $get_stmt = $cass->prepare( "SELECT v FROM numbers" )->get; my ( undef, $result ) = $get_stmt->execute( [] )->get; foreach my $row ( $result->rows_hash ) { say "We have a number " . $row->{v}; }
This module allows use of the CQL3 interface of a Cassandra database. It fully supports asynchronous operation via IO::Async, allowing both direct queries and prepared statements to be managed concurrently, if required. Alternatively, as the interface is entirely based on Future objects, it can be operated synchronously in a blocking fashion by simply awaiting each individual operation by calling the get method.
CQL3
get
It is based on Protocol::CassandraCQL, which more completely documents the behaviours and limits of its ability to communicate with Cassandra.
The node's status has changed. $nodeid is the node's IP address as a text string.
$nodeid
A new node has been added to the cluster, or an existing node has been decommissioned and removed.
These four events are obtained from event watches on the actual node connections and filtered to remove duplicates. The use of multiple primaries should improve the reliability of notifications, though if multiple nodes fail at or around the same time this may go unreported, as no node will ever report its own failure.
The following named parameters may be passed to new or configure:
new
configure
The hostnames of Cassandra node to connect to initially. If more than one host is provided in an array, they will be attempted sequentially until one succeeds during the intial connect phase.
Optional. The service name or port number to connect to.
Optional. Authentication details to use for PasswordAuthenticator.
PasswordAuthenticator
Optional. If set, a USE keyspace query will be issued as part of the connect method.
USE keyspace
Optional. Default consistency level to use if none is provided to query or execute.
query
execute
Optional. The number of primary node connections to maintain. Defaults to 1 if not specified.
Optional. If set, prefer to pick primary nodes from the given data center, only falling back on others if there are not enough available.
Optional. Version of the CQL wire protocol to negotiate during connection. Defaults to 1.
Quotes a string argument suitable for inclusion in an immediate CQL query string.
In general, it is better to use a prepared query and pass the value as an execute parameter though.
Quotes an identifier name suitable for inclusion in a CQL query string.
Connects to the Cassandra node and starts up the connection. The returned Future will yield nothing on success.
Takes the following named arguments:
A set of host names are required, either as a named argument or as a configured value on the object. If the service name is missing, the default CQL port will be used instead.
Stops accepting new queries and prepares all the existing connections to be closed once every outstanding query has been responded to. Returns a future that will eventually yield the CassandraCQL object, when all the connections are closed.
After calling this method it will be an error to invoke query, prepare, execute or the various other methods derived from them.
prepare
Immediately closes all node connections and shuts down the object. Any outstanding or queued queries will immediately fail. Consider this as a "last resort" failure shutdown, as compared to the graceful draining behaviour of close_when_idle.
close_when_idle
Performs a CQL query. On success, the values returned from the Future will depend on the type of query.
For USE queries, the type is keyspace and $result is a string giving the name of the new keyspace.
USE
keyspace
$result
For CREATE, ALTER and DROP queries, the type is schema_change and $result is a 3-element ARRAY reference containing the type of change, the keyspace and the table name.
CREATE
ALTER
DROP
schema_change
For SELECT queries, the type is rows and $result is an instance of Protocol::CassandraCQL::Result containing the returned row data.
SELECT
rows
For other queries, such as INSERT, UPDATE and DELETE, the future returns nothing.
INSERT
UPDATE
DELETE
%other_args may be any of the following, when using cql_version 2 or above:
%other_args
cql_version
Requests the server does not include result metadata in the response. It will be up to the caller to provide this, via set_metadata on the returned Result object, before it can be used.
set_metadata
Requests that the server returns at most the given number of rows. If any further remain, the result object will include the paging_state field. This can be passed in another query call to obtain the next set of data.
paging_state
Requests that the server continues a paged request from this position, given in a previous response.
Sets the consistency level for serial operations in the query. Must be one of CONSISTENCY_SERIAL or CONSISTENCY_LOCAL_SERIAL.
CONSISTENCY_SERIAL
CONSISTENCY_LOCAL_SERIAL
A shortcut wrapper for query which expects a rows result and returns it directly. Any other result is treated as an error. The returned Future returns a Protocol::CassandraCQL::Result directly
Protocol::CassandraCQL::Result
Prepares a CQL query for later execution. On success, the returned Future yields an instance of a prepared query object (see below).
Query objects stored internally cached by the CQL string; subsequent calls to prepare with the same exact CQL string will yield the same object immediately, saving a roundtrip.
Executes a previously-prepared statement, given the binding data. On success, the returned Future will yield results of the same form as the query method. $data should contain a list of encoded byte-string values.
$data
Normally this method is not directly required - instead, use the execute method on the query object itself, as this will encode the parameters correctly.
%other_args may be as for the query method.
The following wrapper methods all wrap the basic query operation.
A shortcut to a SELECT query on system.schema_keyspaces, which returns a result object listing all the keyspaces.
system.schema_keyspaces
Exact details of the returned columns will depend on the Cassandra version, but the result should at least be keyed by the first column, called keyspace_name.
keyspace_name
my $keyspaces = $result->rowmap_hash( "keyspace_name" )
A shortcut to a SELECT query on system.schema_columnfamilies, which returns a result object listing all the columnfamilies of the given keyspace.
system.schema_columnfamilies
Exact details of the returned columns will depend on the Cassandra version, but the result should at least be keyed by the first column, called columnfamily_name.
columnfamily_name
my $columnfamilies = $result->rowmap_hash( "columnfamily_name" )
A shortcut to a SELECT query on system.schema_columns, which returns a result object listing all the columns of the given columnfamily.
system.schema_columns
Exact details of the returned columns will depend on the Cassandra version, but the result should at least be keyed by the first column, called column_name.
column_name
my $columns = $result->rowmap_hash( "column_name" )
Allow other load-balancing strategies than roundrobin.
Adjust connected primary nodes when changing primaries parameter.
primaries
Allow backup nodes, for faster connection failover.
Support LZ4 compression when using CQL version 2.
This is blocked on RT #92825
This code was paid for by
Perceptyx http://www.perceptyx.com/
Shadowcat Systems http://www.shadow.cat
Paul Evans <leonerd@leonerd.org.uk>
To install Net::Async::CassandraCQL, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Net::Async::CassandraCQL
CPAN shell
perl -MCPAN -e shell install Net::Async::CassandraCQL
For more information on module installation, please visit the detailed CPAN module installation guide.