dbd::gofer.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

like to use it.  You do that my adding a \f(CW\*(C`go_last_insert_id_args\*(C'\fR attribute to
the \fIdo()\fR or \fIprepare()\fR method calls. For example:
.PP
.Vb 1
\&    $dbh\->do($sql, { go_last_insert_id_args => [...] });
.Ve
.PP
or
.PP
.Vb 1
\&    $sth = $dbh\->prepare($sql, { go_last_insert_id_args => [...] });
.Ve
.PP
The array reference should contains the args that you want passed to the
\&\fIlast_insert_id()\fR method.
.Sh "execute_for_fetch"
.IX Subsection "execute_for_fetch"
The array methods \fIbind_param_array()\fR and \fIexecute_array()\fR are supported.
When \fIexecute_array()\fR is called the data is serialized and executed in a single
round-trip to the Gofer server. This makes it very fast, but requires enough
memory to store all the serialized data.
.PP
The \fIexecute_for_fetch()\fR method currently isn't optimised, it uses the \s-1DBI\s0
fallback behaviour of executing each tuple individually.
(It could be implemented as a wrapper for \fIexecute_array()\fR \- patches welcome.)
.SH "TRANSPORTS"
.IX Header "TRANSPORTS"
DBD::Gofer doesn't concern itself with transporting requests and responses to and fro.
For that it uses special Gofer transport modules.
.PP
Gofer transport modules usually come in pairs: one for the 'client' DBD::Gofer
driver to use and one for the remote 'server' end. They have very similar names:
.PP
.Vb 2
\&    DBD::Gofer::Transport::<foo>
\&    DBI::Gofer::Transport::<foo>
.Ve
.PP
Sometimes the transports on the \s-1DBD\s0 and \s-1DBI\s0 sides may have different names. For
example DBD::Gofer::Transport::http is typically used with DBI::Gofer::Transport::mod_perl
(DBD::Gofer::Transport::http and DBI::Gofer::Transport::mod_perl modules are
part of the GoferTransport-http distribution).
.Sh "Bundled Transports"
.IX Subsection "Bundled Transports"
Several transport modules are provided with DBD::Gofer:
.PP
\fInull\fR
.IX Subsection "null"
.PP
The null transport is the simplest of them all. It doesn't actually transport the request anywhere.
It just serializes (freezes) the request into a string, then thaws it back into
a data structure before passing it to DBI::Gofer::Execute to execute. The same
freeze and thaw is applied to the results.
.PP
The null transport is the best way to test if your application will work with Gofer.
Just set the \s-1DBI_AUTOPROXY\s0 environment variable to "\f(CW\*(C`dbi:Gofer:transport=null;policy=pedantic\*(C'\fR"
(see \*(L"Using \s-1DBI_AUTOPROXY\s0\*(R" below) and run your application, or ideally its test suite, as usual.
.PP
It doesn't take any parameters.
.PP
\fIpipeone\fR
.IX Subsection "pipeone"
.PP
The pipeone transport launches a subprocess for each request. It passes in the
request and reads the response.
.PP
The fact that a new subprocess is started for each request ensures that the
server side is truly stateless. While this does make the transport \fIvery\fR slow,
it is useful as a way to test that your application doesn't depend on
per-connection state, such as temporary tables, persisting between requests.
.PP
It's also useful both as a proof of concept and as a base class for the stream
driver.
.PP
\fIstream\fR
.IX Subsection "stream"
.PP
The stream driver also launches a subprocess and writes requests and reads
responses, like the pipeone transport.  In this case, however, the subprocess
is expected to handle more that one request. (Though it will be automitically
restarted if it exits.)
.PP
This is the first transport that is truly useful because it can launch the
subprocess on a remote machine using \f(CW\*(C`ssh\*(C'\fR. This means you can now use DBD::Gofer
to easily access any databases that's accessible from any system you can login to.
You also get all the benefits of ssh, including encryption and optional compression.
.PP
See \*(L"Using \s-1DBI_AUTOPROXY\s0\*(R" below for an example.
.Sh "Other Transports"
.IX Subsection "Other Transports"
Implementing a Gofer transport is \fIvery\fR simple, and more transports are very welcome.
Just take a look at any existing transports that are similar to your needs.
.PP
\fIhttp\fR
.IX Subsection "http"
.PP
See the GoferTransport-http distribution on \s-1CPAN:\s0 http://search.cpan.org/dist/GoferTransport\-http/
.PP
\fIGearman\fR
.IX Subsection "Gearman"
.PP
I know Ask Bjo\*/rn Hansen has implemented a transport for the \f(CW\*(C`gearman\*(C'\fR distributed
job system, though it's not on \s-1CPAN\s0 at the time of writing this.
.SH "CONNECTING"
.IX Header "CONNECTING"
Simply prefix your existing \s-1DSN\s0 with "\f(CW\*(C`dbi:Gofer:transport=$transport;dsn=\*(C'\fR"
where \f(CW$transport\fR is the name of the Gofer transport you want to use (see \*(L"\s-1TRANSPORTS\s0\*(R").
The \f(CW\*(C`transport\*(C'\fR and \f(CW\*(C`dsn\*(C'\fR attributes must be specified and the \f(CW\*(C`dsn\*(C'\fR attributes must be last.
.PP
Other attributes can be specified in the \s-1DSN\s0 to configure DBD::Gofer and/or the
Gofer transport module being used. The main attributes after \f(CW\*(C`transport\*(C'\fR, are
\&\f(CW\*(C`url\*(C'\fR and \f(CW\*(C`policy\*(C'\fR. These and other attributes are described below.
.Sh "Using \s-1DBI_AUTOPROXY\s0"
.IX Subsection "Using DBI_AUTOPROXY"
The simplest way to try out DBD::Gofer is to set the \s-1DBI_AUTOPROXY\s0 environment variable.
In this case you don't include the \f(CW\*(C`dsn=\*(C'\fR part. For example:
.PP
.Vb 1
\&    export DBI_AUTOPROXY="dbi:Gofer:transport=null"
.Ve
.PP
or, for a more useful example, try:
.PP
.Vb 1
\&    export DBI_AUTOPROXY="dbi:Gofer:transport=stream;url=ssh:[e-mail]"
.Ve
.Sh "Connection Attributes"
.IX Subsection "Connection Attributes"
These attributes can be specified in the \s-1DSN\s0. They can also be passed in the
\&\e%attr parameter of the \s-1DBI\s0 connect method by adding a "\f(CW\*(C`go_\*(C'\fR" prefix to the name.
.PP
\fItransport\fR
.IX Subsection "transport"
.PP
Specifies the Gofer transport class to use. Required. See \*(L"\s-1TRANSPORTS\s0\*(R" above.
.PP
If the value does not include \f(CW\*(C`::\*(C'\fR then "\f(CW\*(C`DBD::Gofer::Transport::\*(C'\fR" is prefixed.
.PP
The transport object can be accessed via \f(CW$h\fR\->{go_transport}.
.PP
\fIdsn\fR
.IX Subsection "dsn"
.PP
Specifies the \s-1DSN\s0 for the remote side to connect to. Required, and must be last.
.PP
\fIurl\fR
.IX Subsection "url"
.PP
Used to tell the transport where to connect to. The exact form of the value depends on the transport used.
.PP
\fIpolicy\fR
.IX Subsection "policy"
.PP
Specifies the policy to use. See \*(L"\s-1CONFIGURING\s0 \s-1BEHAVIOUR\s0 \s-1POLICY\s0\*(R".
.PP
If the value does not include \f(CW\*(C`::\*(C'\fR then "\f(CW\*(C`DBD::Gofer::Policy\*(C'\fR" is prefixed.
.PP
The policy object can be accessed via \f(CW$h\fR\->{go_policy}.
.PP
\fItimeout\fR
.IX Subsection "timeout"
.PP
Specifies a timeout, in seconds, to use when waiting for responses from the server side.
.PP
\fIretry_limit\fR
.IX Subsection "retry_limit"
.PP
Specifies the number of times a failed request will be retried. Default is 0.
.PP
\fIretry_hook\fR
.IX Subsection "retry_hook"
.PP
Specifies a code reference to be called to decide if a failed request should be retried.
The code reference is called like this:
.PP
.Vb 2
\&  $transport = $h\->{go_transport};
\&  $retry = $transport\->go_retry_hook\->($request, $response, $transport);
.Ve
.PP
If it returns true then the request will be retried, upto the \f(CW\*(C`retry_limit\*(C'\fR.
If it returns a false but defined value then the request will not be retried.
If it returns undef then the default behaviour will be used, as if \f(CW\*(C`retry_hook\*(C'\fR
had not been specified.
.PP
The default behaviour is to retry requests where \f(CW$request\fR\->is_idempotent is true,
or the error message matches \f(CW\*(C`/induced by DBI_GOFER_RANDOM/\*(C'\fR.
.PP
\fIcache\fR
.IX Subsection "cache"
.PP
Specifies that client-side caching should be performed.  The value is the name
of a cache class to use.
.PP
Any class implementing get($key) and set($key, \f(CW$value\fR) methods can be used.
That includes a great many powerful caching classes on \s-1CPAN\s0, including the
Cache and Cache::Cache distributions.
.PP
You can use "\f(CW\*(C`cache=1\*(C'\fR\*(L" is a shortcut for \*(R"\f(CW\*(C`cache=DBI::Util::CacheMemory\*(C'\fR".
See DBI::Util::CacheMemory for a description of this simple fast default cache.
.PP
The cache object can be accessed via \f(CW$h\fR\->go_cache. For example:
.PP
.Vb 1
\&    $dbh\->go_cache\->clear; # free up memory being used by the cache
.Ve
.PP
The cache keys are the frozen (serialized) requests, and the values are the
frozen responses.
.PP
The default behaviour is to only use the cache for requests where
\&\f(CW$request\fR\->is_idempotent is true (i.e., the dbh has the ReadOnly attribute set
or the \s-1SQL\s0 statement is obviously a \s-1SELECT\s0 without a \s-1FOR\s0 \s-1UPDATE\s0 clause.)
.PP
For even more control you can use the \f(CW\*(C`go_cache\*(C'\fR attribute to pass in an
instanciated cache object. Individual methods, including \fIprepare()\fR, can also
specify alternative caches via the \f(CW\*(C`go_cache\*(C'\fR attribute. For example, to
specify no caching for a particular query, you could use
.PP
.Vb 1
\&    $sth = $dbh\->prepare( $sql, { go_cache => 0 } );
.Ve
.PP
This can be used to implement different caching policies for different statements.
.PP
It's interesting to note that DBD::Gofer can be used to add client-side caching
to any (gofer compatible) application, with no code changes and no need for a
gofer server.  Just set the \s-1DBI_AUTOPROXY\s0 environment variable like this:
.PP
.Vb 1
\&    DBI_AUTOPROXY=\*(Aqdbi:Gofer:transport=null;cache=1\*(Aq
.Ve
.SH "CONFIGURING BEHAVIOUR POLICY"
.IX Header "CONFIGURING BEHAVIOUR POLICY"
DBD::Gofer supports a 'policy' mechanism that allows you to fine-tune the number of round-trips to the Gofer server.
The policies are grouped into classes (which may be subclassed) and referenced by the name of the class.
.PP
The DBD::Gofer::Policy::Base class is the base class for all the policy
packages and describes all the available policies.
.PP
Three policy packages are supplied with DBD::Gofer:
.PP
DBD::Gofer::Policy::pedantic is most 'transparent' but slowest because it
makes more  round-trips to the Gofer server.
.PP
DBD::Gofer::Policy::classic is a reasonable compromise \- it's the default policy.
.PP
DBD::Gofer::Policy::rush is fastest, but may require code changes in your applications.
.PP
Generally the default \f(CW\*(C`classic\*(C'\fR policy is fine. When first testing an existing
application with Gofer it is a good idea to start with the \f(CW\*(C`pedantic\*(C'\fR policy
first and then switch to \f(CW\*(C`classic\*(C'\fR or a custom policy, for final testing.
.SH "AUTHOR"
.IX Header "AUTHOR"
Tim Bunce, <http://www.tim.bunce.name>
.SH "LICENCE AND COPYRIGHT"
.IX Header "LICENCE AND COPYRIGHT"
Copyright (c) 2007, Tim Bunce, Ireland. All rights reserved.
.PP
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See perlartistic.
.SH "ACKNOWLEDGEMENTS"
.IX Header "ACKNOWLEDGEMENTS"
The development of DBD::Gofer and related modules was sponsored by
Shopzilla.com (<http://Shopzilla.com>), where I currently work.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
DBI::Gofer::Request, DBI::Gofer::Response, DBI::Gofer::Execute.
.PP
DBI::Gofer::Transport::Base, DBD::Gofer::Policy::Base.
.PP
\&\s-1DBI\s0
.SH "Caveats for specific drivers"
.IX Header "Caveats for specific drivers"
This section aims to record issues to be aware of when using Gofer with specific drivers.
It usually only documents issues that are not natural consequences of the limitations
of the Gofer approach \- as documented avove.
.SH "TODO"
.IX Header "TODO"
This is just a random brain dump... (There's more in the source of the Changes file, not the pod)
.PP
Document policy mechanism
.PP
Add mechanism for transports to list config params and for Gofer to apply any that match (and warn if any left over?)
.PP
Driver-private sth attributes \- set via \fIprepare()\fR \- change \s-1DBI\s0 spec
.PP
add hooks into transport base class for checking & updating a result set cache
   ie via a standard cache interface such as:
   http://search.cpan.org/~robm/Cache\-FastMmap/FastMmap.pm
   http://search.cpan.org/~bradfitz/Cache\-Memcached/lib/Cache/Memcached.pm
   http://search.cpan.org/~dclinton/Cache\-Cache/
   http://search.cpan.org/~cleishman/Cache/
Also caching instructions could be passed through the httpd transport layer
in such a way that appropriate http cache headers are added to the results
so that web caches (squid etc) could be used to implement the caching.
(\s-1MUST\s0 require the use of \s-1GET\s0 rather than \s-1POST\s0 requests.)
.PP
Rework handling of installed_methods to not piggback on dbh_attributes?
.PP
Perhaps support transactions for transports where it's possible (ie null and stream)?
Would make stream transport (ie ssh) more useful to more people.
.PP
Make sth_result_attr more like dbh_attributes (using '*' etc)
.PP
Add \f(CW@val\fR = FETCH_many(@names) to \s-1DBI\s0 in C and use in Gofer/Execute?
.PP
Implement _new_sth in C.