#include <db_cxx.h> int DbEnv::repmgr_start(int nthreads, u_int32_t flags);
The DbEnv::repmgr_start() method starts the Replication Manager.
There are two ways to build Berkeley DB replication applications: the most common approach is to use the Berkeley DB library Replication Manager, where the Berkeley DB library manages the replication group, including network transport, all replication message processing and acknowledgment, and group elections. Applications using the Replication Manager generally make the following calls:
Use DbEnv::repmgr_site() to obtain a DbSite handle, then use that handle to configure the sites in the replication group.
Use DbSite::set_config() to configure sites in the replication group.
Use DbSite::remove() to remove a site from the replication group.
Call DbEnv::repmgr_set_ack_policy() to configure the message acknowledgment policy which best supports the replication group's transactional needs.
Call DbEnv::rep_set_priority() to configure the local site's election priority.
Call DbEnv::repmgr_start() to start the replication application.
For more information on building Replication Manager applications, please see the Replication Getting Started Guide included in the Berkeley DB documentation.
Applications with special needs (for example, applications using network protocols not supported by the Berkeley DB Replication Manager), must perform additional configuration and call other Berkeley DB replication Base API methods. For more information on building Base API applications, please see the Base API Methods section in the Berkeley DB Programmer's Reference Guide.
Starting the Replication Manager consists of opening the TCP/IP listening socket to accept
incoming connections, and starting all necessary background threads. When multiple processes
share a database environment, only one process can open the listening socket; the
DbEnv::repmgr_start() method automatically opens the socket in the
first process to call it, and skips this step in the later calls from
other subordinate processes.
The DbEnv::repmgr_start() method
may not be called before the
DbEnv::open()
method is
called to open the environment. In addition, this method may not be called before
at least one replication site has been configured using the
DbSite class.
In addition, the local environment must be opened with the
DB_THREAD
flag set. If you are starting a view, you must call the
DbEnv::rep_set_view()
method before opening the local environment.
The DbEnv::repmgr_start() method will return
DB_REP_IGNORE
as an informational, non-error return code, if another process has previously become the
TCP/IP listener (though the current call has nevertheless successfully started Replication
Manager's background threads). Unless otherwise specified, the
DbEnv::repmgr_start()
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
Specify the number of threads of control created and dedicated to
processing replication messages. In addition to these message
processing threads, the Replication Manager creates and manages a few
of its own threads of control. The TCP/IP listener
process can change this value after the Replication
Manager is started with a subsequent call to the
DbEnv::repmgr_start() method.
The flags parameter must be set to one of the following values when first starting the Replication Manager:
Start as a master site, and do not call for an election. Note there must never be more than a single master in any replication group, and only one site at a time should ever be started with the DB_REP_MASTER flag specified.
Start as a client, view, or preferred master site, and do not call for an election.
DB_REP_ELECTION
Start as a client, and call for an election if no master is found.
If the Replication Manager is already started, a flags value of 0 can be used when making a subsequent call to change the value of nthreads or when starting a subordinate process.
The DbEnv::repmgr_start()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
The local site tried to join the group, but was unable to do so for some reason (because a master site is not available, or because insufficient clients are running to acknowledge the new site). When that happens the application should pause and retry adding the site until it completes successfully.
If the database environment was not already opened or was
opened without the DB_THREAD flag set; a local
site has not already been configured, this method is called
from a Base API application; a view is being started without
having called the
DbEnv::rep_set_view()
method before opening the database environment; or if an
invalid flag value or parameter was specified.