dbi::profile.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.

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.\" ========================================================================
.\"
.IX Title "DBI::Profile 3"
.TH DBI::Profile 3 "2007-08-09" "perl v5.10.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
DBI::Profile \- Performance profiling and benchmarking for the DBI
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
The easiest way to enable \s-1DBI\s0 profiling is to set the \s-1DBI_PROFILE\s0
environment variable to 2 and then run your code as usual:
.PP
.Vb 1
\&  DBI_PROFILE=2 prog.pl
.Ve
.PP
This will profile your program and then output a textual summary
grouped by query when the program exits.  You can also enable profiling by
setting the Profile attribute of any \s-1DBI\s0 handle:
.PP
.Vb 1
\&  $dbh\->{Profile} = 2;
.Ve
.PP
Then the summary will be printed when the handle is destroyed.
.PP
Many other values apart from are possible \- see \*(L"\s-1ENABLING\s0 A \s-1PROFILE\s0\*(R" below.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The DBI::Profile module provides a simple interface to collect and
report performance and benchmarking data from the \s-1DBI\s0.
.PP
For a more elaborate interface, suitable for larger programs, see
DBI::ProfileDumper and dbiprof.
For Apache/mod_perl applications see
DBI::ProfileDumper::Apache.
.SH "OVERVIEW"
.IX Header "OVERVIEW"
Performance data collection for the \s-1DBI\s0 is built around several
concepts which are important to understand clearly.
.IP "Method Dispatch" 4
.IX Item "Method Dispatch"
Every method call on a \s-1DBI\s0 handle passes through a single 'dispatch'
function which manages all the common aspects of \s-1DBI\s0 method calls,
such as handling the RaiseError attribute.
.IP "Data Collection" 4
.IX Item "Data Collection"
If profiling is enabled for a handle then the dispatch code takes
a high-resolution timestamp soon after it is entered. Then, after
calling the appropriate method and just before returning, it takes
another high-resolution timestamp and calls a function to record
the information.  That function is passed the two timestamps
plus the \s-1DBI\s0 handle and the name of the method that was called.
That data about a single \s-1DBI\s0 method call is called a \fIprofile sample\fR.
.IP "Data Filtering" 4
.IX Item "Data Filtering"
If the method call was invoked by the \s-1DBI\s0 or by a driver then the call is
ignored for profiling because the time spent will be accounted for by the
original 'outermost' call for your code.
.Sp
For example, the calls that the \fIselectrow_arrayref()\fR method makes
to \fIprepare()\fR and \fIexecute()\fR etc. are not counted individually
because the time spent in those methods is going to be allocated
to the \fIselectrow_arrayref()\fR method when it returns. If this was not
done then it would be very easy to double count time spent inside
the \s-1DBI\s0.
.IP "Data Storage Tree" 4
.IX Item "Data Storage Tree"
The profile data is accumulated as 'leaves on a tree'. The 'path' through the
branches of the tree to a particular leaf is determined dynamically for each sample.
This is a key feature of \s-1DBI\s0 profiliing.
.Sp
For each profiled method call the \s-1DBI\s0 walks along the Path and uses each value
in the Path to step into and grow the Data tree.
.Sp
For example, if the Path is
.Sp
.Vb 1
\&  [ \*(Aqfoo\*(Aq, \*(Aqbar\*(Aq, \*(Aqbaz\*(Aq ]
.Ve
.Sp
then the new profile sample data will be \fImerged\fR into the tree at
.Sp
.Vb 1
\&  $h\->{Profile}\->{Data}\->{foo}\->{bar}\->{baz}
.Ve
.Sp
But it's not very useful to merge all the call data into one leaf node (except
to get an overall 'time spent inside the \s-1DBI\s0' total).  It's more common to want
the Path to include dynamic values such as the current statement text and/or
the name of the method called to show what the time spent inside the \s-1DBI\s0 was for.
.Sp
The Path can contain some 'magic cookie' values that are automatically replaced
by corresponding dynamic values when they're used. These magic cookies always
start with a punctuation character.
.Sp
For example a value of '\f(CW\*(C`!MethodName\*(C'\fR' in the Path causes the corresponding
entry in the Data to be the name of the method that was called.
For example, if the Path was:
.Sp
.Vb 1
\&  [ \*(Aqfoo\*(Aq, \*(Aq!MethodName\*(Aq, \*(Aqbar\*(Aq ]
.Ve
.Sp
and the \fIselectall_arrayref()\fR method was called, then the profile sample data
for that call will be merged into the tree at:
.Sp
.Vb 1
\&  $h\->{Profile}\->{Data}\->{foo}\->{selectall_arrayref}\->{bar}
.Ve
.IP "Profile Data" 4
.IX Item "Profile Data"
Profile data is stored at the 'leaves' of the tree as references
to an array of numeric values. For example:
.Sp
.Vb 9
\&  [
\&    106,                  # 0: count of samples at this node
\&    0.0312958955764771,   # 1: total duration
\&    0.000490069389343262, # 2: first duration
\&    0.000176072120666504, # 3: shortest duration
\&    0.00140702724456787,  # 4: longest duration
\&    1023115819.83019,     # 5: time of first sample
\&    1023115819.86576,     # 6: time of last sample
\&  ]
.Ve
.Sp
After the first sample, later samples always update elements 0, 1, and 6, and
may update 3 or 4 depending on the duration of the sampled call.
.SH "ENABLING A PROFILE"
.IX Header "ENABLING A PROFILE"
Profiling is enabled for a handle by assigning to the Profile
attribute. For example:
.PP
.Vb 1
\&  $h\->{Profile} = DBI::Profile\->new();
.Ve
.PP
The Profile attribute holds a blessed reference to a hash object
that contains the profile data and attributes relating to it.
.PP
The class the Profile object is blessed into is expected to
provide at least a \s-1DESTROY\s0 method which will dump the profile data
to the \s-1DBI\s0 trace file handle (\s-1STDERR\s0 by default).
.PP
All these examples have the same effect as each other:
.PP