Notice

This document is for a development version of Ceph.

Perf counters

The perf counters provide generic internal infrastructure for gauges and counters. The counted values can be both integer and float. There is also an “average” type (normally float) that combines a sum and num counter which can be divided to provide an average.

The intention is that this data will be collected and aggregated by a tool like collectd or statsd and fed into a tool like graphite for graphing and analysis. Also, note the Prometheus Module and the Telemetry Module.

Users and developers can also access perf counter data locally to check a cluster’s overall health, identify workload patterns, monitor cluster performance by daemon types, and troubleshoot issues with latency, throttling, memory management, etc. (see Access)

Access

The perf counter data is accessed via the admin socket. For example:

ceph daemon osd.0 perf schema
ceph daemon osd.0 perf dump

Collections

The values are grouped into named collections, normally representing a subsystem or an instance of a subsystem. For example, the internal throttle mechanism reports statistics on how it is throttling, and each instance is named something like:

throttle-msgr_dispatch_throttler-hbserver
throttle-msgr_dispatch_throttler-client
throttle-filestore_bytes
...

Schema

The perf schema command dumps a json description of which values are available, and what their type is. Each named value as a type bitfield, with the following bits defined.

bit

meaning

1

floating point value

2

unsigned 64-bit integer value

4

average (sum + count pair), where

8

counter (vs gauge)

Every value will have either bit 1 or 2 set to indicate the type (float or integer).

If bit 8 is set (counter), the value is monotonically increasing and the reader may want to subtract off the previously read value to get the delta during the previous interval.

If bit 4 is set (average), there will be two values to read, a sum and a count. If it is a counter, the average for the previous interval would be sum delta (since the previous read) divided by the count delta. Alternatively, dividing the values outright would provide the lifetime average value. Normally these are used to measure latencies (number of requests and a sum of request latencies), and the average for the previous interval is what is interesting.

Instead of interpreting the bit fields, the metric type has a value of either gauge or counter, and the value type property will be one of real, integer, real-integer-pair (for a sum + real count pair), or integer-integer-pair (for a sum + integer count pair).

Here is an example of the schema output:

{
  "throttle-bluestore_throttle_bytes": {
      "val": {
          "type": 2,
          "metric_type": "gauge",
          "value_type": "integer",
          "description": "Currently available throttle",
          "nick": ""
      },
      "max": {
          "type": 2,
          "metric_type": "gauge",
          "value_type": "integer",
          "description": "Max value for throttle",
          "nick": ""
      },
      "get_started": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Number of get calls, increased before wait",
          "nick": ""
      },
      "get": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Gets",
          "nick": ""
      },
      "get_sum": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Got data",
          "nick": ""
      },
      "get_or_fail_fail": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Get blocked during get_or_fail",
          "nick": ""
      },
      "get_or_fail_success": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Successful get during get_or_fail",
          "nick": ""
      },
      "take": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Takes",
          "nick": ""
      },
      "take_sum": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Taken data",
          "nick": ""
      },
      "put": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Puts",
          "nick": ""
      },
      "put_sum": {
          "type": 10,
          "metric_type": "counter",
          "value_type": "integer",
          "description": "Put data",
          "nick": ""
      },
      "wait": {
          "type": 5,
          "metric_type": "gauge",
          "value_type": "real-integer-pair",
          "description": "Waiting latency",
          "nick": ""
      }
}

Dump

The actual dump is similar to the schema, except that average values are grouped. For example:

{
  "throttle-msgr_dispatch_throttler-hbserver" : {
     "get_or_fail_fail" : 0,
     "get_sum" : 0,
     "max" : 104857600,
     "put" : 0,
     "val" : 0,
     "take" : 0,
     "get_or_fail_success" : 0,
     "wait" : {
        "avgcount" : 0,
        "sum" : 0
     },
     "get" : 0,
     "take_sum" : 0,
     "put_sum" : 0
  },
  "throttle-msgr_dispatch_throttler-client" : {
     "get_or_fail_fail" : 0,
     "get_sum" : 82760,
     "max" : 104857600,
     "put" : 2637,
     "val" : 0,
     "take" : 0,
     "get_or_fail_success" : 0,
     "wait" : {
        "avgcount" : 0,
        "sum" : 0
     },
     "get" : 2637,
     "take_sum" : 0,
     "put_sum" : 82760
  }
}

Labeled Perf Counters

A Ceph daemon has the ability to emit a set of perf counter instances with varying labels. These counters are intended for visualizing specific metrics in 3rd party tools like Prometheus and Grafana.

For example, the below counters show the number of put requests for different users on different buckets:

{
    "rgw": [
        {
            "labels": {
                "Bucket: "bkt1",
                "User: "user1",
            },
            "counters": {
                "put": 1,
            },
        },
        {
            "labels": {},
            "counters": {
                "put": 4,
            },
        },
        {
            "labels": {
                "Bucket: "bkt1",
                "User: "user2",
            },
            "counters": {
                "put": 3,
            },
        },
    ]
}

All labeled and unlabeled perf counters can be viewed with ceph daemon {daemon id} counter dump.

All labeled and unlabeled perf counter’s schema can be viewed with ceph daemon {daemon id} counter schema.

In the above example the second counter without labels is a counter that would also be shown in ceph daemon {daemon id} perf dump.

Since the counter dump and counter schema commands can be used to view both types of counters it is not recommended to use the perf dump and perf schema commands which are retained for backwards compatibility and continue to emit only non-labeled counters.

Some perf counters that are emitted via perf dump and perf schema may become labeled in future releases and as such will no longer be emitted by perf dump and perf schema respectively.

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