#include <db_cxx.h> int DbEnv::rep_set_config(u_int32_t which, int onoff);
The DbEnv::rep_set_config() method configures the Berkeley DB
replication subsystem.
The database environment's replication subsystem may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "rep_set_config", one or more whitespace characters, and the method which parameter as a string; for example, "rep_set_config DB_REP_CONF_NOWAIT". Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.
The DbEnv::rep_set_config() method configures a database
environment, not only operations performed using the specified
DbEnv handle.
The DbEnv::rep_set_config() method may not be
called to set in-memory replication after the environment is
opened using the
DbEnv::open() method.
This method may also not be called to set master leases after the
DbEnv::rep_start() or
DbEnv::repmgr_start() methods
are called. For all other which
parameters, this method may be called at any time during the life
of the application.
The DbEnv::rep_set_config()
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.
If the onoff parameter is zero, the configuration flag is turned off. Otherwise, it is turned on. All configuration flags are turned off by default.
The which parameter must be set to one of the following values:
The replication master sends groups of records to the clients in a single network transfer.
The client should delay synchronizing to a newly declared master. Clients configured in this way will remain unsynchronized until the application calls the DbEnv::rep_sync() method.
Store internal replication information in memory only.
By default, replication creates files in the environment home directory to preserve some internal information. If this configuration flag is turned on, replication only stores this internal information in-memory and cannot keep persistent state across a site crash or reboot. This results in the following limitations:
A master site should not reappoint itself master immediately after crashing or rebooting because the application would incur a slightly higher risk of client crashes. The former master site should rejoin the replication group as a client. The application should either hold an election or appoint a different site to be the next master.
An application has a slightly higher risk that elections will fail or be unable to complete. Calling additional elections should eventually yield a winner.
An application has a slight risk that the wrong site may win an election, resulting in the loss of some data. This is consistent with the general loss of data durability when running in-memory.
This configuration flag can only be turned on before the environment is opened with the DbEnv::open() method. Its value cannot be changed while the environment is open.
DB_REP_CONF_LEASE
Master leases will be used for this site.
Configuring this option may result in
DB_REP_LEASE_EXPIRED error returns
from the Db::get() and
Dbc::get() methods
when attempting to read entries from a database after the site's
master lease has expired.
This configuration flag may not be set after the DbEnv::repmgr_start() method or the DbEnv::rep_start() method is called.
The replication master will not automatically re-initialize outdated clients.
Berkeley DB method calls that would normally block while clients are in recovery will return errors immediately.
Replication Manager observes the strict "majority" rule in managing elections, even in a group with only 2 sites. This means the client in a 2-site group will be unable to take over as master if the original master fails or becomes disconnected. (See the Elections section in the Berkeley DB Programmer's Reference Guide for more information.) Both sites in the replication group should have the same value for this configuration flag.
The DbEnv::rep_set_config()
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: