Retrieving Debug Information
Each Dgraph data node exposes profile over
/debug/pprof endpoint and metrics over
/debug/vars endpoint. Each Dgraph data node has it’s own profiling and metrics information. Below is a list of debugging information exposed by Dgraph and the corresponding commands to retrieve them.
If you are collecting these metrics from outside the Dgraph instance you need to pass
--expose_trace=true flag, otherwise there metrics can be collected by connecting to the instance over localhost.
Metrics can also be retrieved in the Prometheus format at
/debug/prometheus_metrics. See the Metrics section for the full list of metrics.
Profiling information is available via the
go tool pprof profiling tool built into Go. The “Profiling Go programs” Go blog post will help you get started with using pprof. Each Dgraph Zero and Dgraph Alpha exposes a debug endpoint at
/debug/pprof/<profile> via the HTTP port.
go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/heap Fetching profile from ... Saved Profile in ...
The output of the command would show the location where the profile is stored.
In the interactive pprof shell, you can use commands like
top to get a listing of the top functions in the profile,
web to get a visual graph of the profile opened in a web browser, or
list to display a code listing with profiling information overlaid.
go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/profile
go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/heap
Dgraph by default doesn’t collect the block profile. Dgraph must be started with
--block_rate=<N> with N > 1.
go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/block
The HTTP page
/debug/pprof/ is available at the HTTP port of a Dgraph Zero or Dgraph Alpha. From this page a link to the “full goroutine stack dump” is available (e.g., on a Dgraph Alpha this page would be at
http://localhost:8080/debug/pprof/goroutine?debug=2). Looking at the full goroutine stack can be useful to understand goroutine usage at that moment.
Profiling Information with
Instead of sending a request to the server for each CPU, Memory, and goroutine profile, you can use the
debuginfo command to collect all the profiles you need in one go.
You can run the command like this:
dgraph debuginfo -a <alpha_address:port> -z <zero_address:port> -d <path_to_dir_to_store_profiles>
Your output should look like:
[Decoder]: Using assembly version of decoder Page Size: 4096 I0120 14:57:43.722166 15018 run.go:85] using directory /tmp/dgraph-debuginfo121781350 for debug info dump. I0120 14:57:43.722272 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/goroutine?duration=30 I0120 14:57:43.722281 15018 pprof.go:74] please wait... (30s) I0120 14:57:43.724208 15018 pprof.go:62] saving goroutine profile in /tmp/dgraph-debuginfo121781350/alpha_goroutine.gz I0120 14:57:43.724217 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/heap?duration=30 I0120 14:57:43.724222 15018 pprof.go:74] please wait... (30s) I0120 14:57:43.726212 15018 pprof.go:62] saving heap profile in /tmp/dgraph-debuginfo121781350/alpha_heap.gz I0120 14:57:43.726220 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/threadcreate?duration=30 I0120 14:57:43.726225 15018 pprof.go:74] please wait... (30s) I0120 14:57:43.727054 15018 pprof.go:62] saving threadcreate profile in /tmp/dgraph-debuginfo121781350/alpha_threadcreate.gz I0120 14:57:43.727064 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/block?duration=30 I0120 14:57:43.727071 15018 pprof.go:74] please wait... (30s) I0120 14:57:43.727958 15018 pprof.go:62] saving block profile in /tmp/dgraph-debuginfo121781350/alpha_block.gz I0120 14:57:43.727967 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/mutex?duration=30 I0120 14:57:43.727971 15018 pprof.go:74] please wait... (30s) I0120 14:57:43.728622 15018 pprof.go:62] saving mutex profile in /tmp/dgraph-debuginfo121781350/alpha_mutex.gz I0120 14:57:43.728630 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/profile?duration=30 I0120 14:57:43.728635 15018 pprof.go:74] please wait... (30s) I0120 14:58:13.788794 15018 pprof.go:62] saving profile profile in /tmp/dgraph-debuginfo121781350/alpha_profile.gz I0120 14:58:13.788827 15018 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/trace?duration=30 I0120 14:58:13.788841 15018 pprof.go:74] please wait... (30s) I0120 14:58:14.792110 15018 pprof.go:62] saving trace profile in /tmp/dgraph-debuginfo121781350/alpha_trace.gz I0120 14:58:14.799585 15018 run.go:115] Debuginfo archive successful: dgraph-debuginfo121781350.tar.gz
When the command finishes,
debuginfo returns the tarball’s file name. In this example, it was saved in
-a, --alpha string Address of running dgraph alpha. (default "localhost:8080") -x, --archive Whether to archive the generated report (default true) -d, --directory string Directory to write the debug info into. -h, --help help for debuginfo -p, --profiles strings List of pprof profiles to dump in the report. (default [goroutine,heap,threadcreate,block,mutex,profile,trace]) -s, --seconds uint32 Duration for time-based profile collection. (default 15) -z, --zero string Address of running dgraph zero.
The profile flag (
If needed, you can collect some of them (not necessarily all). For example, this command will collect only
dgraph debuginfo -p goroutine,heap
The seconds flag (
By default, the flag is set to 15 seconds. If you are collecting the CPU profile, this profile needs at least 30 seconds to be collected, therefore when you want to collect it, you need to set the
-s flag as follows:
dgraph debuginfo -s 30
If you don’t set the flag, when collecting a CPU profile you’ll will get a
context deadline exceeded error:
I0120 14:06:49.840613 13589 pprof.go:72] fetching profile over HTTP from http://localhost:8080/debug/pprof/profile?duration=15 I0120 14:06:49.840622 13589 pprof.go:74] please wait... (15s) E0120 14:07:14.341613 13589 pprof.go:58] error while saving pprof profile from http://localhost:8080/debug/pprof/profile?duration=15: http fetch: Get "http://localhost:8080/debug/pprof/profile?duration=15": context deadline exceeded (Client.Timeout exceeded while awaiting headers)
cpu profile: CPU profile determines where a program spends its time while actively consuming CPU cycles (as opposed to while sleeping or waiting for I/O).
heap: Heap profile reports memory allocation samples; used to monitor current and historical memory usage, and to check for memory leaks.
threadcreate: Thread creation profile reports the sections of the program that lead the creation of new OS threads.
goroutine: Goroutine profile reports the stack traces of all current goroutines.
block: Block profile shows where goroutines block waiting on synchronization primitives (including timer channels).
mutex: Mutex profile reports the lock contentions. When you think your CPU is not fully utilized due to a mutex contention, use this profile.
trace: this capture a wide range of runtime events. Execution tracer is a tool to detect latency and utilization problems. You can examine how well the CPU is utilized, and when networking or syscalls are a cause of preemption for the goroutines. Tracer is useful to identify poorly parallelized execution, understand some of the core runtime events, and how your goroutines execute.