CODEWITHSUNDEEP
mysqlc
Adrian Partl
Adrian Partl

Reputation: 76

mysql_real_connect call from within daemon plugin

I want to write a MySQL daemon plugin that monitors queries on other MySQL servers and compares them with queries running on where the daemon is running. Basically this is in a spider engine setting, where a query initiated on the head node get run on the shards. Whenever a query is killed on the head, I want to have a daemon on the shard nodes that will kill the associated query there.

The idea was to initiate a pthread that uses mysql_real_connect, mysql_real_query... to access "show processlist" on the head node and compare them with local thread list. If I issue mysql_real_connect in the thread of the daemon, I get a segmentation fault. I think this is due to a threading issue in mysql_real_connect. I've used #define MYSQL_SERVER 1 and follow the approach taken in ha_federated::real_connect().

Is it actually possible to run mysql_real_connect from within a daemon plugin?

Thanks for any hints.

Upvotes: 2

Views: 259

Answers (1)

Adrian Partl
Adrian Partl

Reputation: 76

After meditating over the handlersocker daemon plugin I realised that in order for mysql_real_connect and friends to work in the daemon thread, a mysql internal thread environment needs to be set up and registered with the server.

This basically involves calling the following in the daemon thread:

my_thread_init();
thd = new THD;

mysql_mutex_lock(&LOCK_thread_count);
thd->thread_id = thread_id++;
mysql_mutex_unlock(&LOCK_thread_count);

thd->store_globals();

... setting up various options in THD ...

mysql_mutex_lock(&LOCK_thread_count);
threads.append(thd);
++thread_count;
mysql_mutex_unlock(&LOCK_thread_count);

Upvotes: 1

Related Questions