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Table Of Contents
Servers, Peer Clients, and Server Groups
A SQLFire server is a process that hosts data and is a member of a peer-to-peer distributed system. SQLFire
servers run in Java Virtual Machines (JVMs).
You start a SQLFire server using the sqlf tool from a command prompt or terminal window. sqlf launches
servers as standalone processes that are akin to database servers. The servers can accept TCP connections from
thin clients, authenticate credentials, manage sessions, delegate work to a thread pool for SQL processing, and
so forth.
A peer client, also known as an embedded client, is a SQLFire-aware JDBC client that connects to the distributed
system using the JDBC peer driver. Peer clients are always connected to the distributed system, and they have
single-hop access to data. A peer client can be congured as a pure client (referred to as an accessor member)
or as a client that also hosts data (a data store).
Both JDBC peer client processes and server processes are peer members of the distributed system. The members
discover each other dynamically through a built-in multicast based discovery mechanism or by using a locator
service when TCP discovery is more desirable.
Note: In addition to peer client members that participate in a cluster, SQLFire servers support thin client
connections from JDBC and ADO.NET thin client drivers. See Developing Java Clients and Peers on
page 105 and Developing ADO.NET Client Applications on page 117.
SQLFire servers and peer clients that host data (when the host-data property is set to true) are automatically
part of the default server group. A server group is a logical grouping of SQLFire server and peer client members
that denes the data stores that should host data for table. When any SQLFire object is created, such as a table,
in the CREATE TABLE statement you can specify the server group name where the table will be hosted. If no
group is specied, the table is hosted in the default server group. Using Server Groups to Manage Data on page
47 provides additional information.
For more information, see:
Starting and Conguring SQLFire Servers on page 215
Using Locators on page 211
Start a SQLFire Peer with the Peer Client JDBC Driver on page 107
Using Server Groups to Manage Data on page 47
Discovery Mechanisms
A peer member (a server or peer client process) announces itself to the distributed system using one of two
mechanisms.
SQLFire provides these discovery mechanisms:
Locator (TCP/IP). A locator service maintains a registry of all peer members in the distributed system at any
given moment. A locator is typically started as a separate process (with redundancy), but you can also embed
a locator in any peer member, such as a SQLFire server. The locator opens a TCP port through which all new
members connect to get initial membership information.
UDP/IP Multicast. Members can optionally use a multicast address to broadcast their presence and receive
membership notication information.
Conguring Discovery Mechanisms on page 211 provides more information.
Group Membership Service
The Group Membership Service (GMS) uses self-dened system membership. Processes can join or leave the
distributed system at any time. The GMS communicates this information to every other member in the system,
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