xSQL High Availability Parameters

The xSQL configuration file can be used to define eXtremeDB High Availability parameters corresponding to the C API mco_ha_params_t structure.

For an overview see page Configuration File Parameters

The ha_params section consists of a set of "name : value" pairs enclosed within braces. For example: 

    ha_params : {
        master_ports : [ ":tcp:6100", ":udp:6100"],
        master_params : {
            ...
        }
        ...
        connection_strings: [ "192.168.1.100:5000", "192.168.1.102:5000" ],
        connect_interval : 1000,
        connect_attempts : 5,
        ...
        replica_params : {
            mode_flags : [ force_sync ],
            ...
        }
    }

The master side master_ports parameter defines one or more listener ports, thus supporting the multi-channel runtime configuration. The replica side connection_strings parameter defines a list of IP addresses to connect to the master in the replica mode. If the connection strings are present, xSQL initializes itself in replica mode and attempts to connect to the list of master nodes defined by this parameter. The number of connect attempts is defined through the connect_attempts parameter and the time interval between the attempts is defined by the value of the connect_interval parameter. If xSQL is unable to connect to either of the master nodes listed in the connection_strings list and the master_ports are present, then xSQL turns into master mode. If the master_ports are undefined, then xSQL quits. Consequently, if the connection_strings are undefined, but the master_ports are, then xSQL runs as a master.

The following table lists the possible options for the ha_params section with the corresponding C API structures and values specified in the comment:

Option,
in "name : example value" form
Description
master_ports : [ ":tcp:6100", ":udp:6100" ],

Address(es) of master(s). Transport-dependend, ":tcp:5000" (or just "5000"), ":udp:5000" or ":pipe:/tmp/test00"

(See also mco_HA_attach_replica() )

master_params : {...}
Master parameters. Corresponds to mco_HA_master_params_t structure (See below Master_Params)
keep_alive_interval : 1000,
Interval between keep-alive messages in milliseconds
trans_window_size : 10,
Transaction window size (See also mco_HA_set_trans_window_size())
connect_timeout : 2000,

Connection timeout period in milliseconds, used on both master and replica sides.

(See mco_HA_attach_master() and mco_HA_attach_replica())

connection_strings: [ "192.168.1.100:5000", "192.168.1.102:5000" ],

Connection string(s). Transport-dependent, ":tcp:192.168.1.100:5000" (or just # "192.168.1.100:5000"), ":udp:192.168.1.100:5000" or ":pipe:/tmp/test00"

xSQL will try to connect to addresses in a round-robin manner

connect_interval : 1000,
Interval between connection attempts in milliseconds, unsigned
connect_attempts : 5,
Maximum number of connect rounds, unsigned
cancel_port : 4321,
Number of port used for cancel socket. If 0, cancellation will be disabled. Default value is 9990
replica_params : {...}
Replica parameters. Corresponds to mco_HA_replica_params_t structure (See below Replica_Params)
switch_mode : "master",

Defines the initial HA switch mode. Possible values are "auto" (default), "master", "replica" or "standalone".

In the "auto" mode, if the xSQLconfiguration file specifies master and replica side parameters, the HA runtime runs xSQL in a replica mode and makes several attempts to connect to the master node. If those attempts are unsuccessful, then xSQLis runs as a master.

In the "master" mode xSQL will only be run s a master, regardless of the replica parameters in its configuration file; in the "replica" mode xSQL only runs as a replica, again regardless of the master parameters in the config file. In the "standalone" mode the xSQL server temporarily ignores HA all together.

(function xsql_ha_set_switch_mode() can be called to change the switch_mode at runtime)

Master_Params

The ha_params::master_params section is defined as follows:

Option,
in "name : example value" form
Description
mode_flags : hotsync,

Master modes & options flags (mco_HA_master_params_t::mode_flags). Combination of

mcast_reliable (MCO_HAMODE_MCAST_RELIABLE),

hotsync (MCO_HAMODE_HOTSYNCH) and

binevolution (MCO_HAMODE_BINEVOLUTION)

(Other modes are enabled automatically - see below)

max_number_of_replicas : 10,
Maximum number of replicas that can connect to master (mco_HA_master_params_t::max_number_of_replicas), unsigned
quorum : 1
Initial value for the HA quorum
async_databuf_size : 100m,

Size of buffer for asynchronous replication in bytes (mco_HA_master_params_t::async_databuf::size), unsigned

(If not 0, enables async replication mode (MCO_HAMODE_ASYNC))

trans_log_length : 100,

Maximum number of transactions stored on master side (mco_HA_master_params_t::trans_log_length), unsigned

(If not 0, enables stateful replication (MCO_HAMODE_STATEFUL_REPLICATION))

commit_timeout : 2000,
Timeout to send transaction in milliseconds (mco_HA_master_params_t::commit_timeout), unsigned
initial_timeout : 60000,
Initial synchronization timeout in milliseconds (mco_HA_master_params_t::initial_timeout), unsigned
synch_timeout : 2000,
Timeout for waiting replica's ACK in milliseconds (mco_HA_master_params_t::synch_timeout), unsigned
detach_timeout : 1000,
Timeout for detaching replica in milliseconds (mco_HA_master_params_t::detach_timeout), unsigned
mcast_address : "224.0.0.1:12345",

Multicast address in form "<IP/hostname>:<port>" or "<port>" (mco_HA_master_params_t::mcast_addr and mco_HA_master_params_t::mcast_port), string

( Enables multicast replication mode (MCO_HAMODE_MCAST))

hotsync_msg_objects : 100,

Number of objects to send at once during hot-synchronization (mco_HA_master_params_t::hotsync_msg_objects), unsigned

(Makes sense only if hotsync mode)

hotsync_msg_size : 100k

Max message size during hot-synchronization in bytes (mco_HA_master_params_t::hotsync_msg_size), unsigned

(Makes sense only if hotsync mode)

compression_level : 9,
The level of compression: 0 - no compression; 1 - best speed, 9 - best compression. Default value is 0
ssl_params : {...}
Master-specific SSL settings. See the global ssl_params section for the description of the parameters and their default values. These parameters override the global settings. To inherit the global ssl_params settings, leave the ssl_params section empty. (They have the same parameters and default values as the global section, except for ca_path and ca_file, which are only allowed in the global section.)

Replica_Params

The ha_params::relica_params section is defined as follows:

Option name : example value
Comment
mode_flags : [ force_sync ],

Modes & options flags (mco_HA_replica_params_t::mode_flags). Combination of

force_master (MCO_HAMODE_FORCE_MASTER) and

force_sync (MCO_HAMODE_FORCE_SYNC)

MCO_HAMODE_EXPLICIT_WRITE_ACCESS

initial_timeout : 60000,
Initial synchronization timeout in milliseconds (mco_HA_replica_params_t::initial_timeout), unsigned
commit_timeout : 2000,
Timeout to receive transaction data from master in milliseconds (mco_HA_replica_params_t::commit_timeout), unsigned
wait_data_timeout : 5000,
Max time between two consecutive transactions in milliseconds (mco_HA_replica_params_t::wait_data_timeout), unsigned
repeat_counter : 3,
Max number of attempts to repeat commit for reliable multicast (mco_HA_replica_params_t::repeat_counter), unsigned
mcast_address : "224.0.0.1:12345",
# Multicast address in form "<IP/hostname>:<port>" or "<port>" (mco_HA_replica_params_t::mcast_addr and mco_HA_replica_params_t::mcast_port), string
initial_commit_policy : no_sync,

Disk commit policy during initial synchronization (mco_HA_replica_params_t::initial_commit_policy) One of :

  • sync_flush (MCO_COMMIT_SYNC_FLUSH),
  • buffered (MCO_COMMIT_BUFFERED),
  • delayed (MCO_COMMIT_DELAYED) or
  • no_sync (MCO_COMMIT_NO_SYNC)
initial_objs_in_trans : 100
Number of objects per transaction during initial synchronization (mco_HA_replica_params_t::initial_objs_in_trans), unsigned
ssl_params : {...}
Replica-specific SSL settings. See the global ssl_params section for the description of the parameters and their default values. These parameters override the global settings. To inherit the global ssl_params settings, leave the ssl_params section empty. (They have the same parameters and default values as the global section, except for ca_path and ca_file, which are only allowed in the global section.)
batch_commit_length : 10,
The maximum number of the transactions (coming from master) that can be merged on the replica side. Default value is 0 (no limit) (See C structure HA_Params for further details)
batch_commit_bsize : 100k,
The maximum total size of the serialized transactions (in bytes) that can be merged on the replica side. This parameter can be used to prevent merging a very large transactions. Default value is 0 (no limit) (See C structure HA_Params for further details)
batch_commit_period : 1000,
The maximum period of time (in milliseconds) that the commit on the replica can be delayed. This parameter helps in cases where master sends some number of transactions and then becomes idle, but batch_commit_length and/or batch_commit_bsize has not been reached. The batch_commit_period ensures that such batch transactions will eventually be commited during the specified period of time. Default value is 1000 (1 second) (See C structure HA_Params for further details)
compression_level : 9,
The level of compression: 0 = no compression; 1 = best speed, 9 - best compression. Default value is 0

Note on Batch Commit Parameters

If both batch_commit_length and batch_commit_bsize are 0, the batch commit is not used (regardless of batch_commit_period value). This is the default behavior.

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