Packages are available for the following platforms:
Packages for the dependencies, libuv (1.x), OpenSSL, and zlib are also provided and can be found under the "dependencies" directory for each platform:
Note: CentOS and Ubuntu use the version of OpenSSL and zlib provided with the distribution.
The driver can also be built from source.
#include <cassandra.h>
/* Use "#include <dse.h>" when connecting to DataStax Enterpise */
#include <stdio.h>
int main() {
/* Setup and connect to cluster */
CassFuture* connect_future = NULL;
CassCluster* cluster = cass_cluster_new();
CassSession* session = cass_session_new();
/* Add contact points */
cass_cluster_set_contact_points(cluster, "127.0.0.1");
/* Provide the cluster object as configuration to connect the session */
connect_future = cass_session_connect(session, cluster);
/* This operation will block until the result is ready */
CassError rc = cass_future_error_code(connect_future);
if (rc != CASS_OK) {
/* Display connection error message */
const char* message;
size_t message_length;
cass_future_error_message(connect_future, &message, &message_length);
fprintf(stderr, "Connect error: '%.*s'\n", (int)message_length, message);
}
/* Run queries... */
cass_future_free(connect_future);
cass_session_free(session);
cass_cluster_free(cluster);
return 0;
}To connect a session, a CassCluster object will need to be created and
configured. The minimal configuration needed to connect is a list of contact
points. The contact points are used to initialize the driver and it will
automatically discover the rest of the nodes in your cluster.
Perfomance Tip: Include more than one contact point to be robust against node failures.
The driver is designed so that no operation will force an application to block.
Operations that would normally cause the application to block, such as
connecting to a cluster or running a query, instead return a CassFuture
object that can be waited on, polled, or used to register a callback.
NOTE: The API can also be used synchronously by waiting on or immediately attempting to get the result from a future.
Queries are executed using CassStatement objects. Statements encapsulate
the query string and the query parameters. Query parameters are not supported
by earlier versions of Cassandra (1.2 and below) and values need to be inlined
in the query string itself.
void execute_query(CassSession* session) {
/* Create a statement with zero parameters */
CassStatement* statement
= cass_statement_new("INSERT INTO example (key, value) VALUES ('abc', 123)", 0);
CassFuture* query_future = cass_session_execute(session, statement);
/* Statement objects can be freed immediately after being executed */
cass_statement_free(statement);
/* This will block until the query has finished */
CassError rc = cass_future_error_code(query_future);
printf("Query result: %s\n", cass_error_desc(rc));
cass_future_free(query_future);
}Cassandra 2.0 supports the use of parameterized queries. This allows the same query string to be executed multiple times with different values; avoiding string manipulation in your application.
Perfomance Tip: If the same query is being reused multiple times, prepared statements should be used to optimize performance.
void execute_paramertized_query(CassSession* session) {
/* There are two bind variables in the query string */
CassStatement* statement
= cass_statement_new("INSERT INTO example (key, value) VALUES (?, ?)", 2);
/* Bind the values using the indices of the bind variables */
cass_statement_bind_string(statement, 0, "abc");
cass_statement_bind_int32(statement, 1, 123);
CassFuture* query_future = cass_session_execute(session, statement);
/* Statement objects can be freed immediately after being executed */
cass_statement_free(statement);
/* This will block until the query has finished */
CassError rc = cass_future_error_code(query_future);
printf("Query result: %s\n", cass_error_desc(rc));
cass_future_free(query_future);
}A single row can be retrieved using the convenience function
cass_result_first_row() to get the first row. A CassIterator object may
also be used to iterate over the returned row(s).
void handle_query_result(CassFuture* future) {
/* This will also block until the query returns */
const CassResult* result = cass_future_get_result(future);
/* If there was an error then the result won't be available */
if (result == NULL) {
/* Handle error */
cass_future_free(future);
return;
}
/* The future can be freed immediately after getting the result object */
cass_future_free(future);
/* This can be used to retrieve the first row of the result */
const CassRow* row = cass_result_first_row(result);
/* Now we can retrieve the column values from the row */
const char* key;
size_t key_length;
/* Get the column value of "key" by name */
cass_value_get_string(cass_row_get_column_by_name(row, "key"), &key, &key_length);
cass_int32_t value;
/* Get the column value of "value" by name */
cass_value_get_int32(cass_row_get_column_by_name(row, "value"), &value);
/* This will free the result as well as the string pointed to by 'key' */
cass_result_free(result);
}The CassCluster object describes a Cassandra cluster’s configuration. The
default cluster object is good for most clusters and only requires a single or
multiple list of contact points in order to establish a session connection.
Once a session is connected using a cluster object its configuration is
constant. Modifying the cluster object configuration once a session is
established does not alter the session's configuration.
The CassSession object is used for query execution. Internally, a session
object also manages a pool of client connections to Cassandra and uses a load
balancing policy to distribute requests across those connections. An
application should create a single session object per keyspace as a session
object is designed to be created once, reused, and shared by multiple threads
within the application. The throughput of a session can be scaled by
increasing the number of I/O threads. An I/O thread is used to handle reading
and writing query request data to and from Cassandra. The number of I/O threads
defaults to one per CPU core, but it can be configured using
cass_cluster_set_num_threads_io(). It’s generally better to create a single
session with more I/O threads than multiple sessions with a smaller number of
I/O threads. More DataStax driver best practices can be found in this post.
Each I/O thread maintains a small number of connections for each node in the Cassandra cluster and each of those connections can handle several simultaneous requests using pipelining. Asynchronous I/O and pipelining together allow each connection to handle several (up to 32k with protocol v3/v4) in-flight requests concurrently. This significantly reduces the number of connections required to be open to Cassandra and allows the driver to batch requests destined for the same node.
A CassSession is designed to be used concurrently from multiple threads.
CassFuture is also thread safe. Other than these exclusions, in general,
functions that might modify an object's state are NOT thread safe. Objects
that are immutable (marked 'const') can be read safely by multiple threads.
NOTE: The object/resource free-ing functions (e.g. cass_cluster_free,
cass_session_free, ... cass_*_free) cannot be called concurrently on the
same instance of an object.
Values such as strings (const char*), bytes and decimals
(const cass_bytes_t*) point to memory held by the result object. The
lifetimes of these values are valid as long as the result object isn’t freed.
These values must be copied into application memory if they need to live
longer than the result object’s lifetime. Primitive types such as
cass_int32_t are copied by the driver because it can be done cheaply
without incurring extra allocations.
NOTE: Advancing an iterator invalidates the value it previously returned.
Here are some features that are missing from the C/C driver, but are included with other drivers. The schedule for these features can be found on JIRA.
- Compression
- Schema event registration and notification
- Callback interfaces for load balancing, authentication, reconnection and retry