drms_server - Manages a database session and passes database requests to database from client modules
[DRMS Utilities]

Start a DRMS server program. More...

Collaboration diagram for drms_server - Manages a database session and passes database requests to database from client modules:

Synopsis:

drms_server [FLAGS] [SESSION_ARGUMENTS]

drms_server creates a DRMS session enabling multiple modules to run in the same session.

				      drms_server				      
		    +----------------------------------------------+		      
		    |                          	                   |		      
     +----------+   |   +--------+ +--------+++	 +-------------+   |		      
     |          |   |   |        +-+   in   ||+--+             |   |		      
     |   SUMS   +---+---+  SUMS  | +--------+++	 |             +---+-------- client 0 
     |          |   |   | thread | +++--------+	 |             |   |		      
     |          |   |   |        +-+|| out    +--+             +---+-------- client 1 
     +----------+   |   +--------+ +++--------+	 |             |   |		      
                    |   +--------+             	 |             |   |		      
                    |   |        |             	 |             |   |		      
                    |   | signal ----------------+             +---+-------- client n
                    |   | thread |               |    server   |   |
		    |   |      	 |               | thread pool |   |
	 	    |   +--------+               +------++-----+   |
		    +-----------------------------------++---------+
		                                 +------++-----+
						 |             |
						 |     	DB     |
						 |             |
						 +-------------+

The drms_server - Manages a database session and passes database requests to database from client modules is designed to support multiple client modules running at the same time. It performs the following major tasks:

• Connection to DRMS DB.

  drms_server - Manages a database session and passes database requests to database from client modules opens a single DB connection. This DB connection is shared by all modules connected to the same drms_server - Manages a database session and passes database requests to database from client modules program via sockets. Such shared DB connection makes drms_commit() issued from the client modules extremely hazardous, e.g., one client module can inadvadently commit another client module data. The correct usage of drms_commit requires higher level coordination among the client modules.

• Communication with SUMS

  drms_server - Manages a database session and passes database requests to database from client modules talks the SUMS via SUMS API. All the interactions with SUMS are happenning in the SUMS thread, drms_sums_thread. This thread retrieves SUMS request from the sum_inbox, and places SUMS reply in sum_outbox. Both sum_inbox and sum_outbox are FIFO queues with the thread id as tag. They are shared memory. Don't insert local variable into the queue unless you are sure to get the reply back before the local variable vanishes. Due to FIFO queue implementation, only the head of the queue is examined. if the head is not removed, nothing behind it can be removed.

  	producer	consumer
  sum_inbox	any call to SUMS API	drms_sums_thread
  sum_outbox	drms_sums_thread	function that needs SUMS call reply

• Exiting: either abort or commit

  The closing sequence can be tricky, one might run into race condition if not careful. There are two exit routes: drms_server_commit() and drms_server_abort().

  1. drms_server_commit()

        drms_delete_temporaries() removes all records created as DRMS_TRANSIENT
        drms_commit_all_units() commits all data units (does not include log SU)
        drms_server_close_session() {
         fflush() on stdout and stderr
         restore_stder()
         drms_commit() log SU
         update drms_session table entry
        }
        wait for SUMS threads to finish via pthread_join()
        disconnect stat db connection
        db_commit() for data db connection
        db_abort()  for data db connection?
        drms_free_env()
     

  2. drms_server_abort()

        db_rollback() on db data connection
        drms_server_close_session()
        add to sums inbox/outbox to thaw thread that may be waiting
        disconnect stat db connection
        db_abort() for data db connection
        sleep() to wait for other threads to finish cleanly.
        drms_free_env()
     

The signal thread

FLAGS (can be grouped together):

-h: Show drms_server - Manages a database session and passes database requests to database from client modules usage information.

-V: Run drms_server - Manages a database session and passes database requests to database from client modules in verbose mode.

-Q: Run drms_server - Manages a database session and passes database requests to database from client modules in quiet mode.

-f: Run drms_server - Manages a database session and passes database requests to database from client modules in the foreground. Without -f drms_server - Manages a database session and passes database requests to database from client modules spawns a server in a background process, prints the connection info to stdout and exits.

-L: Redirect stdout and stderr to SU log files.

-n: Turn off Nagle's algorithm on TCP/IP sockets.

-s: Set noshare which turns off the serializable mode for the database.

SESSION_ARGUMENTS:

To specify an argument that affects properties of the DRMS session, use param=value, where param is one of the following.

• JSOC_DBHOST Specifies (overrides) the database host to connect to. Default is DBNAME
• JSOC_DBNAME Specifies (overrides) the database name to use. Default is DBNAME
• JSOC_DBUSER Specifies (overrides) the username used during database host connection. Default is USER.
• JSOC_DBPASSWD Specifies (overrides) the password for the username. Default is PASSWD.
• JSOC_SESSIONNS Specifies (overrides) the DRMS session namespace.
• DRMS_RETENTION Sets (forces) the storage-unit retention time for all <modules> in the DRMS session. The environment is not searched for this keyword.
• DRMS_ARCHIVE Sets (forces) the storage-unit archive flag for all <module>s in the DRMS session. The default is to let the client module or JSD prevail. Values are not given -> INT_MIN, or -1, 0, 1. The environment is not searched for this keyword.
• DRMS_QUERY_MEM Sets the memory maximum for a database query.
• DRMS_SERVER_WAIT Non-zero value indicates waiting 2 seconds before exiting, otherwise don't wait.

See also:

create_series - create a new DRMS series from a .jsd file describe_series - print summary information about a series delete_series - delete an existing DRMS series modify_series show_info - Examine a dataseries structure or contents