VIRTUAL_DB module

Admin Guide

Overview

The idea

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), round-robin.

Therefore: each virtual db url with associated real dbs and a way to use(mode) it’s real dbs must be specified.

Modes

The implemented modes are:

• FAILOVER - Use the first URL; if it fails, take the next URL and redo the operation.
• PARALLEL - Use all the URLs in the virtual DB URL set. Fails if all the URLs fail.
• ROUND (round-robin) - Use the next URL each time; if it fails, use the next one, redo operation.

There are conceptual limitations to the above modes with respect to the operation. For example in parallel mode it is ok to insert into multiple dbs the same value but it is bad to query multiple dbs into the same result. This implementation threats such operation as it would be in failover mode.

  Conceptual allowed(1) and not allowed(0) operations
                          parallel    round
    dbb->use_table
    dbb->init
    dbb->close
    dbb->query              0           1
    dbb->fetch_result       0           0
    dbb->raw_query          0           1
    dbb->free_result        0           0
    dbb->insert             1           1
    dbb->delete             1           0
    dbb->update             1           0
    dbb->replace            1           0
    dbb->last_inserted_id   0           0
    dbb->insert_update      1           1

Note

The capabilities returned are the minimum common denominator of all the dbs in the set. The capabilities are reduced even more based on the mode of the set (PARALLEL, ROUND).

Note

The capabilities will not be reduced for PARALLEL mode but conceptual not allowed operations will be done on a single db. Ex: query will only query one db.

Failures

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

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 doesnt matter.

Dependencies

OpenSIPS Modules

The following modules must be loaded before this module:

• At least one real db module.

External Libraries or Applications

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

• None.

Exported Parameters

db_urls (str)

Multiple value parameter used for virtual db urls declaration.

Set db_urls parameter

...

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")
...

db_probe_time (integer)

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).

Set db_probe_time parameter

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

db_max_consec_retrys (integer)

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).

Set db_max_consec_retrys parameter

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

Exported MI Functions

db_get

Return information about global state of the real dbs.

Name: db_get

Parameters:

• None.

MI FIFO Command Format:

db_get
_empty_line_

db_set

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

Sets the reconnect reset flag.

Name: db_set

Parameters:

• set_index [int]
• db_url_index [int]
• may_use_db_flag [boolean]
• ignore db_max_consec_retrysboolean

db_set 3 2 0 1 means:

• 3 - the fourth set (must exist)
• 2 - the third url in the fourth set(must exist)
• 0 - processes are not allowed to use that url
• 1 - reset and suppress db_max_consec_retrys

MI FIFO Command Format:

db_set 3 2 0 1
_empty_line_

Contributors

By Commit Statistics

Top contributors by DevScore⁽¹⁾, authored commits⁽²⁾ and lines added/removed⁽³⁾

#	Name	DevScore	Commits	Lines++	Lines—
1.	Razvan Pistolea	32	7	2258	311
2.	Stefan Darius (@dariusstefan)	10	5	337	76
3.	Bogdan-Andrei Iancu (@bogdan-iancu)	6	4	6	4
4.	Anca Vamanu	3	1	3	3
5.	Razvan Crainea (@razvancrainea)	3	1	2	2

(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)

(2) including any documentation-related commits, excluding merge commits

(3) ignoring whitespace edits, renamed files and auto-generated files

By Commit Activity

#	Name	Commit Activity
1.	Stefan Darius (@dariusstefan)	Jun 2026 - Jul 2026
2.	Razvan Crainea (@razvancrainea)	Jun 2026 - Jun 2026
3.	Anca Vamanu	Jan 2011 - Jan 2011
4.	Bogdan-Andrei Iancu (@bogdan-iancu)	Aug 2009 - Dec 2009
5.	Razvan Pistolea	Jul 2009 - Aug 2009

(1) including any documentation-related commits, excluding merge commits

Documentation

Contributors

Last edited by: Razvan Crainea (@razvancrainea), Razvan Pistolea.

License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0