guys- i just uploaded a new 3.0.0 snapshot to http://matt-massie.com/ganglia/ganglia-3.0.0.200410211518.tar.gz
if you diff this snapshot with a previous snapshot you will see
significant code change.
the new in-memory filesystem uses string tables (hashes) instead of
linked-lists now for improved performance (much faster lookup times) and
the code has been simplified and cleaned up. the new code also allows
the creation of anonymous filesystems which can then be
attached/detached to another filesystem. this is necessary to correctly
trend data that is collected. (explained below)
here is a more in-depth explanation of how gangliad will work given
these new capabilities.
if you look at ./gangliad/gangliad.c, around line 32 you'll see the
module_thread() function. this is the heart of how gangliad will
process data. in pseudo-code each module thread looks like...
------------------- start module thread -------------------------
gangliaDir current_data = NULL;
gangliaDir previous_data = NULL;
gangliaDir new_data = NULL;
gangliaDir timechange_data = NULL;
gangliaDir valuechange_data = NULL;
gangliaDir lost_data = NULL;
for(;;)
{
if(current_data)
{
/* We have data from our last collection so
detach/disconnect it from the exported data tree.
The data is not deleted just detached. */
gangliaDirOrphan( current_data );
if( previous_data )
{
/* Delete all the data from our last last collection. */
gangliaDirFree( previous_data );
}
/* Save the pointer to the last data we collected */
previous_data = current_data;
}
/* Create a fresh "anonymous" data structure */
current_data = gangliaDirCreate( NULL );
/* Call the module and pass the pointer to this fresh structure */
module_function( current_data );
/* The current data now holds all the latest metrics as populated
by the module. This data is a hierarchical filesystem. */
if( current_data && previous_data )
{
/* Delete all the data from the last diff we did */
gangliaDirFree( new_data );
gangliaDirFree( timechange_data );
gangliaDirFree( valuechange_data );
gangliaDirFree( lost_data );
/* We compare the current data to the previously collected data
and pass these diffs to our alert modules */
/* All data in current that is not in previous */
new_data = find_all_new_data( current_data, previous_data );
/* All data that has changed in value significantly since
last collection */
valuechange_data = find_all_value_change_data( current_data,
previous_data );
/* All data that has change in time significantly since
last collection */
timechange_data = find_all_time_change_data( current_data,
previous_data );
/* All data in previous that is not in current */
lost_data = find_all_lost_data( current_data, previous_data);
/* At this point, we run any alert modules that are defined */
for( module = alert_new_modules; module; module = module->next )
{
module->function( new_data );
}
/* etc etc etc for value/time threshold and lost data */
for(...)
for(...)
}
/* Connect our current data (which is currently not attached)
to the exported filesystem */
gangliaDirAdopt( exported_filesystem, current_data );
} /* end for(;;) loop */
-------------------- end module thread pseudo-code ---------------------
i hope this code is pretty clear. it over simplifies things a bit but
it you look at the code in ./gangliad/gangliad.c you'll see it's not
much different really.
i think in my mind of a 3D molecular model. what gangliad does is
analyze the molecular structure.... compare it to what the structure
last was and act on those changes (jokes about heisenberg aside). each
module is responsible for processing a particular branch/chain of the
overall structure.
you'll see that this snapshot also has a mod_ganglia2_xml module. i'll
clean up the code a bit more and build some alert modules to show you
how they will work very soon.
-matt
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