db_virtual Module

A virtual DB will expose the same front DB api however, it will backed by many real DB. This means that a virtual DB URL translates to many real DB URLs. This virtual layer also enables us to use the real dbs in multiple ways such as: parallel, failover(hotswap) and round-robin. Therefore: each virtual DB URL with associated real dbs and a way to use(mode) it's real dbs must be specified.

The implemented modes are:

When choosing the db virtual mode, be sure that there is a full compatibility between the DB operations you want to do (inserts, updates, deletes,...) and the relation (if any) between the real DB URLs you have in the set - can be completely independent, can be nodes of the same cluster, or any other combination.

For each set (or new virtual DB URL), the capabilities are automatically calculated based on the capabilities provided by the real DB URLs from the set. A logical AND is done for each cabability over all the URLs in the set. Shortly, in order for the virtual URL to provide a certain capability, ALL its real URLs must provide that capability.

Note that starting with version 2.2 db_virtual supports async_raw_query and async_raw_resume functions currently implemented only by the mysql database engine.

	When an operation from a process on a real DB fails:
		it is marked (global and local CAN flag down)
		its connection closed

	Later a timer process (probe):
	foreach virtual db_url
		foreach real db_url
			if global CAN down
				try to connect
			if ok
				global CAN up
				close connection

	Later each process:
		if local CAN down and global CAN up
			if db_max_consec_retrys *
				try to connect
		if ok
			local CAN up

				

Note *: there could be inconsistencies between the probe and each process so a retry limit is in order. It is reset and ignored by an MI command.

The timer process(probe) is a process that tries to reconnect to failed dbs from time to time. It is a separate process so that when it blocks (for a timeout on the connection) it doesn't matter.

The following modules must be loaded before this module:

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

Multiple value parameter used for virtual DB URLs declaration.

...

modparam("group","db_url","virtual://set1")
modparam("presence|presence_xml", "db_url","virtual://set2")

modparam("db_virtual", "db_urls", "define set1 PARALLEL")
modparam("db_virtual", "db_urls", "mysql://opensips:opensipsrw@localhost/testa")
modparam("db_virtual", "db_urls", "postgres://opensips:opensipsrw@localhost/opensips")

modparam("db_virtual", "db_urls", "define set2 FAILOVER")
modparam("db_virtual", "db_urls", "mysql://opensips:opensipsrw@localhost/testa")
...
				

Time interval after which a registered timer process attempts to check failed(as reported by other processes) connections to real dbs. The probe will connect and disconnect to the failed real DB and announce others.

Default value is 10 (10 sec).

...
modparam("db_virtual", "db_probe_time", 20)
...
				

After the timer process has reported that it can connect to the real db, other processes will try to reconnect to it. There are cases where although the probe could connect some might fail. This parameter represents the number of consecutive failed retries that a process will do before it gives up. This value is reset and suppressed by a MI function(db_set).

Default value is 10 (10 consecutive times).

...
modparam("db_virtual", "db_max_consec_retrys", 20)
...

				

Return information about global state of the real dbs.

Name: db_get

Parameters:

MI FIFO Command Format:

				db_get
				_empty_line_
			

Sets the permissions for real dbs access per set per db.

Sets the reconnect reset flag.

Name: db_set

Parameters:

db_set 3 2 0 1 means:

MI FIFO Command Format:

				db_set 3 2 0 1
				_empty_line_