# Exporting Data In Ganglia Format

### Introduction

With the release of Collectl Version 3.3.1, one can now send collectl data directly to a ganglia gmond in binary format using the custom export gexpr.ph. This results in several benefits for existing users of ganglia:

- You can now get the benefit of collecting all the data collectl can generate at a very low overheard.
- Since all collectl instances send this data at the same time, system noise on clusters running fine-grained parallel jobs is reduced.
- You can still log all the data collectl collects locally and only send a subset to gmond, making it possible to collect far more data than ganglia can handle without overwhelming the gmetad. This is especially important on large clusters. In fact, if you choose you can have collectl only send ganglia the core data it currently provide graphs for.
- And finally, you can monitor as frequently as you like and send data to ganglia at a coarser frequency.

As of V3.5 of collectl, the experimental status of this capability has been lifted since enough people are currently using it to verify it works as described.

### Ganglia Configuration

The following figure shows one possible configuration of a large cluster running ganglia and is only intended to be illustrative. For complete documentation on how to set up and configure ganglia see the official wiki.

This configuration assumes one has set up ganglia gmonds in a hierarchy, such that those at the bottom of the tree collect system statistics and send them up to a higher level aggregation gmond and ultimately percolate up to the gmetad which writes the data to a round-robin database.

To use collectl as a data source there are 2 alternatives. In the diagram below at the left you simply have collectl send data to a local gmond to supplement whatever data it is already collecting, noting there won't be any way to record any of gmond's data locally. The diagram at the right would replace all gmonds and have collectl do all the data collection, optionall logging data locally, and sending data to an aggregation level gmond. Whatever method you chose you must ensure the gmond(s) are listening on their udp receive channel and enable the ganglia communications feature in collectl as described in the following sections. There are probably other hybrid configurations which are beyond the scope of this document as well as this author.

One last component is configuring the rrd to use the metrics being supplied by collectl and the details of that discussion are beyond the scope of this document as well.

### Usage

Like any other custom export used by collectl, you tell collectl to use gexpr with --export gexpr and in addition include the gmond hostname:port followed by one or more of the standard switches. There are also 2 more switched unique to gexpr and they are:

- g - only send core variables to gmond, using the standard names gmond has predefined graphs for (see the second verification example below).
- G - send core variables to gmond, using the standard names gmond has predefined graphs for, but also include any additional variables collected by collectl and possibly filtered by gexpr's s switch

The following example shows collectl gathering data on many system components but only sending cpu, disk, memory and network data to a gmond on system gmond using port 8108. It also sends a set of data every 20 seconds while writing the data to a file in plot format to a local file in /tmp every 5 seconds.

This module also supports sending its output to a multicast address, which is used if hostname in an address in the range of 225.0.0.0 through 239.255.255.255. To use this feature you will have to first install IO::Socket::Multicast which in turn requires the module IO::Socket::Interface be installed as well. Note that both these modules may be updated and so you should verify you're actually installing the latest one.

    collectl -scdfijmntx --export gexpr,gmond:8108,s=cdmn,i=20 -i5 -f /tmp -P

### Verification

There are 2 ways to make sure everything is working as expected, the first is to make sure you're using the ganglia export module correctly and to do this you can use the debugging parameter. Like collectl itself, which has its own debugging variable (see d), the value of this debugging variable should be interpreted as setting a bit mask, where each bit results in different behavior. Refer to the header of gexpr for the complete set, noting the following example uses only 1 bit, namely the one for printing the data being set over the socket. If for some reason you want to simultaneously disable actually sending the data over the socket to ganglia use the debugging value of 8 or a combined value of 8. Note that in this latter case you are still required to supply a socket:port because they will be opened but also realize you can use just about anything you want since no data is actually sent over it.

     collectl -scd --export gexpr,192.168.253.168:2222,d=1

     07:32:11.004 Name: cputotals.user       Units: percent               Val: 0
     07:32:11.004 Name: cputotals.nice       Units: percent               Val: 0
     07:32:11.004 Name: cputotals.sys        Units: percent               Val: 0
     07:32:11.004 Name: cputotals.wait       Units: percent               Val: 0
     07:32:11.004 Name: cputotals.irq        Units: percent               Val: 0
     07:32:11.004 Name: cputotals.soft       Units: percent               Val: 0
     07:32:11.004 Name: cputotals.steal      Units: percent               Val: 0
     07:32:11.004 Name: cputotals.idle       Units: percent               Val: 99
     07:32:11.004 Name: ctxint.ctx           Units: switches/sec          Val: 173
     07:32:11.004 Name: ctxint.int           Units: intrpts/sec           Val: 1031
     07:32:11.004 Name: ctxint.proc          Units: pcreates/sec          Val: 4
     07:32:11.004 Name: ctxint.runq          Units: runqSize              Val: 238
     07:32:11.005 Name: disktotals.reads     Units: reads/sec             Val: 0
     07:32:11.005 Name: disktotals.readkbs   Units: readkbs/sec           Val: 0
     07:32:11.005 Name: disktotals.writes    Units: writes/sec            Val: 0
     07:32:11.005 Name: disktotals.writekbs  Units: writekbs/sec          Val: 0

This second example shows the use of the g option which only sends the core ganglia data using ganglia variable naming. Also notice a nifty trick that since we're telling gexpr not to send the data over a socket, we can use a dummy network address/port and same ourselves some typing. Also note that since we didn't select memory or network stats, they aren't sent to ganglia either.

     collectl -scd --export gexpr,1.2.3.4:5,d=9,g

     05:43:19.003 Name: cpu_user             Units: percent      Val:        0 TTL: 5 sent
     05:43:19.004 Name: cpu_nice             Units: percent      Val:        0 TTL: 5 sent
     05:43:19.004 Name: cpu_system           Units: percent      Val:        1 TTL: 5 sent
     05:43:19.004 Name: cpu_wio              Units: percent      Val:        0 TTL: 5 sent
     05:43:19.004 Name: cpu_idle             Units: percent      Val:       99 TTL: 5 sent
     05:43:19.004 Name: cpu_aidle            Units: percent      Val:       99 TTL: 5 sent
     05:43:19.005 Name: cpu_num              Units: CPUs         Val:        1 TTL: 5 sent
     05:43:19.005 Name: proc_total           Units: Load/Procs   Val:      141 TTL: 5 sent
     05:43:19.005 Name: proc_run             Units: Load/Procs   Val:        0 TTL: 5 sent
     05:43:19.005 Name: load_one             Units: Load/Procs   Val:        0 TTL: 5 sent
     05:43:19.005 Name: load_five            Units: Load/Procs   Val:        0 TTL: 5 sent
     05:43:19.006 Name: load_fifteen         Units: Load/Procs   Val:        0 TTL: 5 sent

Assuming you're now successfully calling gexpr and can see the output above, it's time to make sure it is going to the expected gmond. The easiest way to do this is to simply run the gmond with debugging enabled at a level of at least 2 and make sure it can see the data from collectl, being sure you haven't set a debug level of 8 in gexpr. If it can see data in gmond (note that only the variable names and not their values are reported by gmond), you're done. If not, you need to make sure gmond is correctly listening for udp data and that the port it expects to see data on is in fact the one gexpr is sending to. If all looks correct, it may be necessary to watch the network traffic with a tool like udpdump or wireshark.

This is an example of what you should expect to see, noting that in this case gmond is still configured to collect its standard metrics, which can be disabled in gmond.conf since you no longer need these.

     gmond -d 2
     loaded module: core_metrics
     loaded module: cpu_module
     loaded module: disk_module
     loaded module: load_module
     loaded module: mem_module
     loaded module: net_module
     loaded module: proc_module
     loaded module: sys_module
     udp_recv_channel mcast_join=NULL mcast_if=NULL port=8108 bind=NULL
     tcp_accept_channel bind=NULL port=8109
     Processing a metric metadata message from cag-dl585-02.cag
     ***Allocating metadata packet for host--cag-dl585-02.cag-- and metric --cputotals.user-- ****
     saving metadata for metric: cputotals.user host: cag-dl585-02.cag
     Processing a metric value message from cag-dl585-02.cag
     ***Allocating value packet for host--cag-dl585-02.cag-- and metric --cputotals.user-- ****
     saving metadata for metric: cputotals.nice host: cag-dl585-02.cag

updated Feb 21, 2011