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< p > Library Version 11.2.5.2< / p >
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< th colspan = "3" align = "center" > DbEnv::rep_set_config()< / th >
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Replication Methods
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< h2 class = "title" style = "clear: both" > < a id = "repconfig" > < / a > DbEnv::rep_set_config()< / h2 >
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< pre class = "programlisting" > #include < db_cxx.h>
int
DbEnv::rep_set_config(u_int32_t which, int onoff); < / pre >
< p >
The < code class = "methodname" > DbEnv::rep_set_config()< / code > method configures the Berkeley DB
replication subsystem.
< / p >
< p >
The database environment's replication subsystem may also be
configured using the environment's < a href = "../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class = "olink" > DB_CONFIG< / a > 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 < span class = "bold" > < strong > which< / strong > < / span > parameter as a
string and optionally one or more whitespace characters, and the
string "on" or "off". If the optional string is omitted, the
default is "on"; for example, "rep_set_config DB_REP_CONF_NOWAIT"
or "rep_set_config DB_REP_CONF_NOWAIT on". Because the < a href = "../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class = "olink" > DB_CONFIG< / a >
file is read when the database environment is opened, it will
silently overrule configuration done before that time.
< / p >
< p >
The < code class = "methodname" > DbEnv::rep_set_config()< / code > method configures a database
environment, not only operations performed using the specified
< a class = "link" href = "env.html" title = "Chapter > DbEnv< / a > handle.
< / p >
< p >
The < code class = "methodname" > DbEnv::rep_set_config()< / code > method may not be
called to set in-memory replication after the environment is
opened using the
< a class = "xref" href = "envopen.html" title = "DbEnv::open()" > DbEnv::open()< / a > method.
This method may also not be called to set master leases after the
< a class = "xref" href = "repstart.html" title = "DbEnv::rep_start()" > DbEnv::rep_start()< / a > or
< a class = "xref" href = "repmgrstart.html" title = "DbEnv::repmgr_start()" > DbEnv::repmgr_start()< / a > methods
are called. For all other < span class = "bold" > < strong > which< / strong > < / span >
parameters, this method may be called at any time during the life
of the application.
< / p >
< p >
The < code class = "methodname" > DbEnv::rep_set_config()< / code > < span >
< span >
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.
< / span >
< / span >
< / p >
< div class = "sect2" lang = "en" xml:lang = "en" >
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< h3 class = "title" > < a id = "id3639960" > < / a > Parameters< / h3 >
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< h4 class = "title" > < a id = "id3639956" > < / a > which< / h4 >
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< p >
The < span class = "bold" > < strong > which< / strong > < / span > parameter must be set to
one of the following values:
< / p >
< div class = "itemizedlist" >
< ul type = "disc" >
< li >
< p > < a id = "config_DB_REP_CONF_AUTOINIT" > < / a >
< code class = "literal" > DB_REP_CONF_AUTOINIT< / code >
< / p >
< p >
The replication master will automatically re-initialize outdated
clients. This option is turned on by default.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REP_CONF_BULK" > < / a >
< code class = "literal" > DB_REP_CONF_BULK< / code >
< / p >
< p >
The replication master sends groups of records to the clients in a
single network transfer.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REP_CONF_DELAYCLIENT" > < / a >
< code class = "literal" > DB_REP_CONF_DELAYCLIENT< / code >
< / p >
< p >
The client should delay synchronizing to a newly declared master.
Clients configured in this way will remain
unsynchronized until the application calls the
< a class = "xref" href = "repsync.html" title = "DbEnv::rep_sync()" > DbEnv::rep_sync()< / a > method.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REP_CONF_INMEM" > < / a >
< code class = "literal" > DB_REP_CONF_INMEM< / code >
< / p >
< p >
Store internal replication information in memory only.
< / p >
< p >
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:
< / p >
< div class = "itemizedlist" >
< ul type = "circle" >
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< p >
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.
< / p >
< / li >
< li >
< p >
An application has a slightly higher risk that elections will fail or be
unable to complete. Calling additional elections should eventually yield a
winner.
< / p >
< / li >
< li >
< p >
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.
< / p >
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< / ul >
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< p >
This configuration flag can only be turned on before the environment
is opened with the < a class = "xref" href = "envopen.html" title = "DbEnv::open()" > DbEnv::open()< / a >
method. Its value cannot be changed while the environment is open.
All sites in the replication
group should have the same value for this
configuration flag.
< / p >
< / li >
< li >
< p >
< code class = "literal" > DB_REP_CONF_LEASE< / code >
< / p >
< p >
Master leases will be used for this site.
< / p >
< p >
Configuring this option may result in
< code class = "literal" > DB_REP_LEASE_EXPIRED< / code > error returns
from the < a class = "xref" href = "dbget.html" title = "Db::get()" > Db::get()< / a > and
< a class = "xref" href = "dbcget.html" title = "Dbc::get()" > Dbc::get()< / a > methods
when attempting to read entries from a database after the site's
master lease has expired.
< / p >
< p >
This configuration flag may not be set after the
< a class = "xref" href = "repmgrstart.html" title = "DbEnv::repmgr_start()" > DbEnv::repmgr_start()< / a > method or the
< a class = "xref" href = "repstart.html" title = "DbEnv::rep_start()" > DbEnv::rep_start()< / a >
method is called. All sites in the replication
group should have the same value for this
configuration flag.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REP_CONF_NOWAIT" > < / a >
< code class = "literal" > DB_REP_CONF_NOWAIT< / code >
< / p >
< p >
Berkeley DB method calls that would normally block while clients are
in recovery will return errors immediately.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REPMGR_CONF_ELECTIONS" > < / a >
< code class = "literal" > DB_REPMGR_CONF_ELECTIONS< / code >
< / p >
< p >
Replication Manager automatically runs elections to
choose a new master when the old master appears to
have become disconnected. This option is turned on
by default.
< / p >
< p >
If this option is turned off, the application is
responsible for assigning the new master
explicitly, by calling the
< code class = "methodname" > DB_ENV-> repmgr_start()< / code >
method.
< / p >
< div class = "caution" style = "margin-left: 0.5in; margin-right: 0.5in;" >
< h3 class = "title" > Caution< / h3 >
< p >
Most Replication Manager
applications should accept the default automatic
behavior. Allowing two sites in a replication
group to act as master simultaneously can lead to
loss of data.
< / p >
< / div >
< p >
In an application with multiple processes per
database environment, only the main replication
process may change this configuration setting.
< / p >
< / li >
< li >
< p > < a id = "config_DB_REPMGR_CONF_2SITE_STRICT" > < / a >
< code class = "literal" > DB_REPMGR_CONF_2SITE_STRICT< / code >
< / p >
< p >
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
< a href = "../../programmer_reference/rep_elect.html" class = "olink" > Elections< / a >
section in the < em class = "citetitle" > Berkeley DB Programmer's Reference Guide< / em > for more information.)
Both sites in the replication group should have the same value for this
configuration flag. This option is turned on by
default.
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< h4 class = "title" > < a id = "id3640116" > < / a > onoff< / h4 >
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< p >
If the < span class = "bold" > < strong > onoff< / strong > < / span > parameter
is zero, the configuration flag is turned off.
Otherwise, it is turned on. Most configuration flags are
turned off by default, exceptions are noted above.
< / p >
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< h3 class = "title" > < a id = "id3640092" > < / a > Errors< / h3 >
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< p >
The < code class = "methodname" > DbEnv::rep_set_config()< / code > < span >
< span >
method may fail and throw a < a class = "link" href = "dbexception.html" title = "Chapter > DbException< / a >
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
< / span >
< / span >
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< h4 class = "title" > < a id = "id3640255" > < / a > EINVAL< / h4 >
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< p >
If setting in-memory replication after the database environment is already
opened; if setting master leases after replication is started; if setting
the 2-site strict majority rule for a Base API application;
or if an invalid flag value or parameter was specified.
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< a class = "link" href = "env.html" title = "Chapter > DbEnv< / a >
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< h3 class = "title" > < a id = "id3640364" > < / a > See Also< / h3 >
2011-09-13 17:44:24 +00:00
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< p >
< a class = "xref" href = "rep.html#replist" title = "Replication and Related Methods" > Replication and Related Methods< / a >
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