21-11-2005
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Registrado: sep 2004
Ubicación: En algún lugar.
Posts: 32.057
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Te pego lo que dice el libro "The Firebird eBook"
Cita:
Comparing Superserver and Classic Server Architecture
While Superserver and Classic server share many common characteristics—indeed,
they are built from the same codebase—they present quite distinct models of oper-
ation under the hood.
Executable and Processes
Classic server runs one server process per connection, on demand (see Figure 36-1).
When a client attempts to connect to a Firebird database, an instance of the fb_inet_server
executable is initiated and remains dedicated to that client connection for the duration
of the connection. When the client detaches from the database, the server process
instance ends.
Superserver runs as a single invocation of the fbserver executable.
fbserver is started once, by a system boot script or by the system administrator, and
stays running, waiting for connection requests. The process is terminated by an explicit
shutdown.
Lock Management
On Classic server, each client’s server process has its own, dedicated database cache
and multiple processes contend for access to the database. A lock manager subsystem,
Configuration and Special Features
fb_lock_mgr, uses inter-process communication (IPC) methods to arbitrate and syn-
chronize concurrent page access among the processes.
On Superserver, the lock manager is implemented as a thread within the fbserver
process and uses inter-thread communication mechanisms instead of POSIX signaling.
For a detailed overview of lock manager internals, refer to Chapter 40.
Resource Use
On Classic server, each instance of fb_inet_server is allocated a static cache of database
pages in its memory space. Resource growth per additional client connection is there-
fore linear. However, when the number of concurrent connections is relatively low,
Classic server uses fewer overall resources.
Superserver employs a single cache space that is shared by client attachments,
allowing more efficient use and management of cache memory when the number of
simultaneous connections grows larger.
Local Access Method
Classic server permits application processes that are running on the same machine as
the server and databases to perform I/O on database files directly.
Except for the Embedded Server, Superserver requires applications to use a
network method for I/O requests and satisfies those requests by proxy. On Linux,
Superserver does not support direct local access.
• On non-Windows platforms (and recommended for Windows too) local con-
nections to Superserver are made through the localhost server (at IP address
127.0.0.1, by convention).
• A Windows server and local client can simulate a network connection in the
shared IPC space. This mechanism, referred to as the local access method, can-
not handle multiple connections safely. Beyond Firebird 1.5, it is superseded by
a local access method using the XNET subsystem.
Embedded Server can use only the “Windows local” access method and supports
one and only one connection to each local database. The embedded client can connect
to multiple local databases exclusively and access them through the embedded server.
The embedded client can also connect as a regular network client to databases on
other servers.
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