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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.

Metrics Information

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.

curl http://<IP>:<HTTP_PORT>/debug/vars

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

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.

CPU Profile

go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/profile

Memory Profile

go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/heap

Block Profile

Dgraph by default doesn’t collect the block profile. Dgraph must be started with --profile_mode=block and --block_rate=<N> with N > 1.

go tool pprof http://<IP>:<HTTP_PORT>/debug/pprof/block

Goroutine stack

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 debuginfo

Instead of sending a request to the server for each CPU, memory, and goroutine profile, you can use the debuginfo command to collect all of these profiles, along with several metrics.

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:

I0311 14:13:53.243667   32654 run.go:118] using directory /tmp/dgraph-debuginfo037351492 for debug info dump.
I0311 14:13:53.243864   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/heap
I0311 14:13:53.243872   32654 debugging.go:70] please wait... (30s)
I0311 14:13:53.245338   32654 debugging.go:58] saving heap metric in /tmp/dgraph-debuginfo037351492/alpha_heap.gz
I0311 14:13:53.245349   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/profile?seconds=30
I0311 14:13:53.245357   32654 debugging.go:70] please wait... (30s)
I0311 14:14:23.250079   32654 debugging.go:58] saving cpu metric in /tmp/dgraph-debuginfo037351492/alpha_cpu.gz
I0311 14:14:23.250148   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/state
I0311 14:14:23.250173   32654 debugging.go:70] please wait... (30s)
I0311 14:14:23.255467   32654 debugging.go:58] saving state metric in /tmp/dgraph-debuginfo037351492/alpha_state.gz
I0311 14:14:23.255507   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/health
I0311 14:14:23.255528   32654 debugging.go:70] please wait... (30s)
I0311 14:14:23.257453   32654 debugging.go:58] saving health metric in /tmp/dgraph-debuginfo037351492/alpha_health.gz
I0311 14:14:23.257507   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/jemalloc
I0311 14:14:23.257548   32654 debugging.go:70] please wait... (30s)
I0311 14:14:23.259009   32654 debugging.go:58] saving jemalloc metric in /tmp/dgraph-debuginfo037351492/alpha_jemalloc.gz
I0311 14:14:23.259055   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/trace?seconds=30
I0311 14:14:23.259091   32654 debugging.go:70] please wait... (30s)
I0311 14:14:53.266092   32654 debugging.go:58] saving trace metric in /tmp/dgraph-debuginfo037351492/alpha_trace.gz
I0311 14:14:53.266152   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/metrics
I0311 14:14:53.266181   32654 debugging.go:70] please wait... (30s)
I0311 14:14:53.276357   32654 debugging.go:58] saving metrics metric in /tmp/dgraph-debuginfo037351492/alpha_metrics.gz
I0311 14:14:53.276414   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/vars
I0311 14:14:53.276439   32654 debugging.go:70] please wait... (30s)
I0311 14:14:53.278295   32654 debugging.go:58] saving vars metric in /tmp/dgraph-debuginfo037351492/alpha_vars.gz
I0311 14:14:53.278340   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/trace?seconds=30
I0311 14:14:53.278366   32654 debugging.go:70] please wait... (30s)
I0311 14:15:23.286770   32654 debugging.go:58] saving trace metric in /tmp/dgraph-debuginfo037351492/alpha_trace.gz
I0311 14:15:23.286830   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/goroutine?debug=2
I0311 14:15:23.286886   32654 debugging.go:70] please wait... (30s)
I0311 14:15:23.291120   32654 debugging.go:58] saving goroutine metric in /tmp/dgraph-debuginfo037351492/alpha_goroutine.gz
I0311 14:15:23.291164   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/block
I0311 14:15:23.291192   32654 debugging.go:70] please wait... (30s)
I0311 14:15:23.304562   32654 debugging.go:58] saving block metric in /tmp/dgraph-debuginfo037351492/alpha_block.gz
I0311 14:15:23.304664   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/mutex
I0311 14:15:23.304706   32654 debugging.go:70] please wait... (30s)
I0311 14:15:23.309171   32654 debugging.go:58] saving mutex metric in /tmp/dgraph-debuginfo037351492/alpha_mutex.gz
I0311 14:15:23.309228   32654 debugging.go:68] fetching information over HTTP from http://localhost:8080/debug/pprof/threadcreate
I0311 14:15:23.309256   32654 debugging.go:70] please wait... (30s)
I0311 14:15:23.313026   32654 debugging.go:58] saving threadcreate metric in /tmp/dgraph-debuginfo037351492/alpha_threadcreate.gz
I0311 14:15:23.385359   32654 run.go:150] Debuginfo archive successful: dgraph-debuginfo037351492.tar.gz

When the command finishes, debuginfo returns the tarball’s file name. If no destination has been specified, the file will be created in the same directory from where you ran the debuginfo command.

The following files contain the metrics collected by the debuginfo command:

dgraph-debuginfo639541060
├── alpha_block.gz
├── alpha_goroutine.gz
├── alpha_health.gz
├── alpha_heap.gz
├── alpha_jemalloc.gz
├── alpha_mutex.gz
├── alpha_profile.gz
├── alpha_state.gz
├── alpha_threadcreate.gz
├── alpha_trace.gz
├── zero_block.gz
├── zero_goroutine.gz
├── zero_health.gz
├── zero_heap.gz
├── zero_jemalloc.gz
├── zero_mutex.gz
├── zero_profile.gz
├── zero_state.gz
├── zero_threadcreate.gz
└── zero_trace.gz

Command parameters

  -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
  -m, --metrics strings    List of metrics & profiles to dump in the report. (default [heap,cpu,state,health,jemalloc,trace,metrics,vars,trace,goroutine,block,mutex,threadcreate])
  -s, --seconds uint32     Duration for time-based metric collection. (default 30)
  -z, --zero string        Address of running dgraph zero.

The metrics flag (-m)

By default, debuginfo collects:

  • heap
  • cpu
  • state
  • health
  • jemalloc
  • trace
  • metrics
  • vars
  • trace
  • goroutine
  • block
  • mutex
  • threadcreate

If needed, you can collect some of them (not necessarily all). For example, this command will collect only jemalloc and health profiles:

dgraph debuginfo -m jemalloc,health

Profiles details

  • 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.

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