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index a6b48cc60916252b6d28b954b6982c920ea5328d..2544a08cb73791fae720d67dfd7e282942b20fb5 100644 (file)
--- a/doc/rrdgraph_libdbi.pod
+++ b/doc/rrdgraph_libdbi.pod
@@ -121,11 +121,11 @@ To illustrate this here a command to create a graph that contains the actual val
* Naturally you can also use any other kind of driver that libdbi supports - e.g postgres, ...
-* From the way the datasource is joined, it should also be possible to do joins over different tables
+* 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 datasource string.
+* 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
@@ -138,6 +138,18 @@ To illustrate this here a command to create a graph that contains the actual val
* 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