=head1 NAME

rrdgraph_libdbi - fetching data for graphing in rrdtool graph via libdbi

=head1 SYNOPSIS

E<lt>rrdfileE<gt> = B<sql//E<lt>libdbi driverE<gt>/E<lt>driver-option-nameE<gt>=E<lt>driver-option-valueE<gt>/...[/rrdminstepsize=E<lt>stepsizeE<gt>][/rrdfillmissing=E<lt>fill missing n samplesE<gt>]//E<lt>tableE<gt>/E<lt>unixtimestamp columnE<gt>/E<lt>data value columnE<gt>[/derive]/E<lt>where clause 1E<gt>/.../E<lt>where clause nE<gt>>

=head1 DESCRIPTION

This pseudo-rrd-filename defines a sql datasource:

=over 8

=item B<sql//>

  magic cookie-prefix for a libdbi type datasource

=item B<E<lt>libdbi driverE<gt>>

  which libdbi driver to use (e.g: mysql)

=item B<E<lt>driver-option-nameE<gt>>=B<E<lt>driver-option-valueE<gt>>

  defines the parameters that are required to connect to the database with the given libdbi driver
  (These drivers are libdbi dependent - for details please look at the driver documentation of libdbi!)

=item B</rrdminstepsize>=B<E<lt>minimum step sizeE<gt>>

  defines the minimum number of the step-length used for graphing (default: 300 seconds)

=item B</rrdfillmissing>=B<E<lt>fill missing stepsE<gt>>

  defines the number of steps to fill with the last value to avoid NaN boxes due to data-insertation jitter (default: 0 steps)

=item B<E<lt>tableE<gt>>

  defines the table from which to fetch the resultset.

  If there is a need to fetch data from several tables, these tables can be defined by separating the tablenames with a "+"

  hex-type-encoding via %xx are translated to the actual value, use %% to use %

=item B<E<lt>[*]unixtimestamp columnE<gt>>

  defines the column of E<lt>tableE<gt> which contains the unix-timestamp 
  - if this is a DATETIME field in the database, then prefix with leading '*'

  hex-type-encoding via %xx are translated to the actual value, use %% to use %

=item B<E<lt>data value columnE<gt>>

  defines the column of E<lt>tableE<gt> which contains the value column, which should be graphed

  hex-type-encoding via %xx are translated to the actual value, use %% to use %

=item B</derive>

  defines that the data value used should be the delta of the 2 consecutive values (to simulate COUNTER or DERIVE type datasources)

=item B</E<lt>where clause(s)E<gt>>

  defines one (ore more) where clauses that are joined with AND to filter the entries in the <lt>table<gt>

  hex-type-encoding via %xx are translated to the actual value, use %% to use %

=back

the returned value column-names, which can be used as ds-names, are:

=over 8

=item B<min>, B<avg>, B<max>, B<count> and B<sigma>

  are returned to be used as ds-names in your DS definition.
  The reason for using this is that if the consolidation function is used for min/avg and max, then the engine is used several times.
  And this results in the same SQL Statements used several times

=back

=head1 EXAMPLES

Here an example of a table in a MySQL database:

  DB connect information
    dbhost=127.0.0.1
    user=rrd
    password=secret
    database=rrd

  here the table:
    CREATE TABLE RRDValue (
      RRDKeyID      bigint(20) NOT NULL,
      UnixTimeStamp int(11) NOT NULL,
      value         double default NOT NULL,
      PRIMARY KEY  (RRDKeyID,UnixTimeStamp)
    );

and the RRDKeyID we want to graph for is: 1141942900757789274

The pseudo rrd-filename to access this is:
"sql//mysql/host=127.0.0.1/dbname=rrd/username=rrd/password=secret//RRDValue/UnixTimeStamp/value/RRDKeyID=1141464142203608274"

To illustrate this here a command to create a graph that contains the actual values.

  DS_BASE="sql//mysql/host=127.0.0.1/dbname=rrd/username=rrd/password=passwd//RRDValue/UnixTimeStamp/value/RRDKeyID=1141942900757789274"
  rrdtool graph test.png --imgformat=PNG --start=-1day --end=+3hours --width=1000 --height=600 \
    "DEF:min=$DS_BASE:min:AVERAGE" \
    "LINE1:min#FF0000:value" \
    "DEF:avg=$DS_BASE:avg:AVERAGE" \
    "LINE1:avg#00FF00:average" \
    "DEF:max=$DS_BASE:max:AVERAGE" \
    "LINE1:max#FF0000:max" \
    "DEF:sigma=$DS_BASE:sigma:AVERAGE" \
    "CDEF:upper=avg,4,sigma,*,+" \
    "LINE1:upper#0000FF:+4 sigma" \
    "CDEF:lower=avg,4,sigma,*,-" \
    "LINE1:lower#0000FF:-4 sigma"

=head1 NOTES

* Naturally you can also use any other kind of driver that libdbi supports - e.g postgres, ...

* From the way the data source is joined, it should also be possible to do joins over different tables 
  (separate tables with "," in table and add in the WHERE Clauses the table equal joins. 
  This has not been tested!!!)

* It should also be relatively simple to add to the database using the same data source string.
  This has not been implemented...

* The aggregation functions are ignored and several data columns are used instead 
  to avoid querying the same SQL several times when minimum, average and maximum are needed for graphing...

* for DB efficiency you should think of having 2 tables, one containing historic values and the other containing the latest data.
  This second table should be kept small to allow for the least ammount of blocking SQL statements.
  Whith mysql you can even use myisam table-type for the first and InnoDB for the second. 
  This is especially interresting as with tables with +100M rows myisam is much smaller then InnoDB.

* To debug the SQL statements set the environment variable RRDDEBUGSQL and the actual SQL statements and the timing is printed to stderr.



=head1 Performance issues with MySQL backend

LibDBI has a big performance issue when you retrieve data from a MySQL server. Performance impact is exponentially based on the number of 
values you retrieve from the database. 
For example, it would take more than 2 seconds to graph 5DS on 150 hours of data with a precision of 5 minutes 
(against 100ms when data comes from a RRD file). This bug has been fixed on latest version of LibDBI (not release yet). 
At that time, you would need to compile libdbi and libdbi-drivers from CVS repository to fix it.
You can find more informations on this libdbi-users mailing list thread : http://sourceforge.net/mailarchive/message.php?msg_id=30320894


=head1 BUGS

* at least on Linux please make sure that the libdbi driver is explicitly linked against libdbi.so.0 
  check via ldd /usr/lib/dbd/libmysql.so, that there is a line with libdbi.so.0. 
  otherwise at least the perl module RRDs will fail because the dynamic linker can not find some symbols from libdbi.so.
  (this only happens when the libdbi driver is actually used the first time!)
  This is KNOWN to be the case with RHEL4 and FC4 and FC5! (But actually this is a bug with libdbi make files!)

* at least version 0.8.1 of libdbiexhibits a bug with BINARY fields
  (shorttext,text,mediumtext,longtext and possibly also BINARY and BLOB fields), 
  that can result in coredumps of rrdtool. 
  The tool will tell you on stderr if this occures, so that you know what may be the reason.
  If you are not experiencing these coredumps, then set the environment variable RRD_NO_LIBDBI_BUG_WARNING, 
  and then the message will not get shown.

=head1 AUTHOR

Martin Sperl <rrdtool@martin.sperl.org>
