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From Sebastian Estevez <sebastian.este...@datastax.com>
Subject Re: How to integrate Cassandra C driver in another open source server
Date Fri, 17 Apr 2015 15:49:08 GMT
You may want to try the c++ driver mailing list:

https://groups.google.com/a/lists.datastax.com/forum/#!forum/cpp-driver-user

All the best,


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Sebastián Estévez

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On Fri, Apr 17, 2015 at 10:32 AM, TOURON, BENOIT <benoit.touron@atos.net>
wrote:

> Hi,
>
> We are working on a project which consists in a DB migration (move from a
> proprietary solution to Cassandra).
> Among the modules communicating with the DB, there is a Radius Server,
> based on the open source FreeRadius 2.2. So we have modified the source
> code of this server and added a specific module to call Cassandra, but we
> have an issue.
> We are using the DataStax C driver. The FreeRadius is in multithread mode,
> with pthreads.
>
> Our modifications are the following :
>
> *       In the instantiate part of the module (called once by the main
> process at the beginning), we do the following code
>
> ape_main_context = (APE_MAIN_CONTEXT *) malloc(sizeof(APE_MAIN_CONTEXT));
> ape_main_context->cluster = cass_cluster_new();
> cass_cluster_set_contact_points(ape_main_context->cluster, "dse5");
>
> The APE_MAIN_CONTEXT is a structure used to pass info between the threads,
> which contains among other information, the Cassandra cluster.
> Once the cluster is created (with only 1 contact point, called "dse5"), we
> continue with the following code :
>
> ape_main_context->session = cass_session_new();
> CassFuture* connect_future =
> cass_session_connect_keyspace(ape_main_context->session,
> ape_main_context->cluster, "ape01");
> CassError rc = cass_future_error_code(connect_future);
> cass_future_free(connect_future);
>
> This will create the session in the main process.
>
> *       In the authorize part of the module (which is called in a worker
> thread, spawn by the main process), we actually call the Cassandra DB, with
> the following code :
>
> CassString insert_query = cass_string_init("select * from ape01.session
> where ip_user= ? ;");
> CassStatement* statement = cass_statement_new(insert_query, 1);
> cass_statement_bind_string(statement, 0,
> cass_string_init("10000FFFFFF10000FFFFFF1000000001"));
> CassFuture* query_future =
> cass_session_execute(request->thread_context->main_context->session,
> statement);
> CassResult* result = cass_future_get_result(query_future);
> if (result == NULL) {
>         printf("rlm_cassandra : Query result KO");
>         return RLM_MODULE_HANDLED;
> }
> cass_future_free(query_future);
> CassRow* row = cass_result_first_row(result);
> CassString key;
> cass_value_get_string(cass_row_get_column_by_name(row, "ip_user"), &key);
> printf("rlm_cassandra : resultat ip_user : <%s>\n",key.data);
> cass_result_free(result);
> cass_statement_free(statement);
>
>
> When we start the server, we notice that the instantiate part of the
> modules is executed without error (we have added some logs).
> However, when we use a Radius client to send an authorize request, the
> module function is launched in a worker thread, but remains blocked
> somewhere.
> We suspect a signal issue. The call flow would be the following :
>
> *       Call the instantiate function of the module (create the Cassandra
> cluster and session)
> *       Initialize other things (free radius code), erasing a signal
> handler which is useful for the Cassandra driver
> *       Spawn the worker threads and enter an event loop in each thread
> *       On reception of a request, a worker thread handles it and gets
> blocked
>
> As a workaround, we have moved the creation  of the Cassandra session in
> the beginning of the working thread (before entering the event loop). We
> create only 1 session (we use a mutex and a static Boolean first=true at
> the beginning and set to false in the protected code).
> So the call flow becomes :
>
> *       Call the instantiate function of the module (create the Cassandra
> cluster only)
> *       Initialize other things (free radius code)
> *       Spawn the worker threads, create 1 Cassandra session for all
> threads (static Boolean + mutex), and enter an event loop in each thread
> *       On reception of a request, a worker thread handles it and it works
>
> So, we manage to make a Cassandra call with a workaround, if the Cassandra
> session is created after the FreeRadius init.
>
> Finally, to confirm the idea, we have written a standalone module, in C
> with a main process spawning threads with exactly the same schema.
> In this case, the call flow becomes :
>
> *       Call the instantiate function of the module (create the Cassandra
> cluster and session)
> *       Spawn the worker threads which make a call to Cassandra using the
> cluster and session created in the main process. The call works.
>
> Our questions are the following :
>
> *       Is the "signal" idea credible for you ?
> *       Do you know the useful signals for the Cassandra driver ?
> *       Is it a possibility to use another signal which would be
> compatible with freeRadius ?
> *       Any other idea to resolve this issue ?
>
> Many thanks in advance.
>
> Ben
>
>
>

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