Slow Operations Logging

how-to

Tracing information on slow operations can be found in the logs as threshold logging, orphan logging, and other span metrics. Change the settings to alter how much information you collect

To improve debuggability certain metrics are automatically measured and logged. These include slow queries, responses taking beyond a certain threshold, and orphaned responses.

Observability Metrics

Individual request traces present a very specific (and isolated) view of the system. In addition, it also makes sense to capture information that aggregates request data (i.e. requests per second), but also data which is not tied to a specific request at all (i.e. resource utilization).

The deployment situation itself is similar to the tracer: either applications already have a metrics infrastructure in place or they don’t. The difference is that exposing some kind of metrics is much more common than request based tracing, because most production deployments at least monitor CPU usage etc.

Configuring Metrics Logging

The metrics logging can be enabled/disabled, and the emit interval can be configured, in the connection string or via lcb_cntl calls. See the metrics reporting options.

At each emit/log interval, libcouchbase logs a JSON structure with the per-operation latencies in a simple histogram. The default value for the emitInterval is 600 seconds (10 minutes).

JSON Output Format & Logging

The overall structure looks like this (here prettified for readability):

{
  “meta”: {
	“emit_interval_s”: 600,
  }
  “<service-a>”: {
      “total_count”: 1234,
      “percentiles_us”: {
        “50.0”: 5,
        “90.0”: 10,
        “99.0”: 33,
        “99.9”: 55,
        “100.0”: 101,
      }
    }
  },
}

For each service and each node, the total count and the latency percentiles are reported. This will help during debugging to get a decent idea of the latency distribution across services and nodes. For more sophisticated grouping and aggregations, users can use custom implementations, such as OpenTelemetry.

The emit_interval_s is reported in the meta section of the JSON output since to calculate the ops/s the total_count needs to be divided by the emit_interval_s. Since the configuration property is not always available when debugging logs it is included to make it simple.

Threshold Logging Reporting

Threshold logging is the recording of slow operations — useful for diagnosing when and where problems occur in a distributed environment.

Configuring Threshold Logging

To configure threshold logging, adjust the tracing threshold logging options. You should expect to see output in JSON format in the logs for the services encountering problems:

{
  "<service-a>": {
    "total_count": 1234,
    "top_requests": [{<entry>}, {<entry>},...]
  },
  "<service-b>": {
    "total_count": 1234,
    "top_requests": [{<entry>}, {<entry>},...]
  },
}

The total_count represents the total amount of over-threshold recorded items in each interval per service. The number of entries in “top_requests” is configured by the sampleSize. The service placeholder is replaced with each service — “kv”, “query”, etc. Each entry looks like this, with all fields populated:

{
  "total_duration_us": 1200,
  "encode_duration_us": 100,
  "last_dispatch_duration_us": 40,
  "total_dispatch_duration_us": 40,
  "last_server_duration_us": 2,
  "total_server_duration_us": 2,
  "operation_name": "upsert",
  "last_local_id": "66388CF5BFCF7522/18CC8791579B567C",
  "operation_id": "0x23",
  "last_local_socket": "10.211.55.3:52450",
  "last_remote_socket": "10.112.180.101:11210",
  "timeout_ms": 75000
}

If a field is not present (because for example dispatch did not happen), it will not be included.

Orphaned Requests Logging

Orphan requests logging acts as an auxiliary tool to the tracing and metrics capabilities. It does not expose an external API to the application and is very focussed on its feature set.

The way it works is that every time a response is in the process of being completed, when the SDK detects that the original caller is not listening anymore (likely because of a timeout), it will send this “orphan” response to a reporting utility which then aggregates it and in regular intervals logs them in a specific format.

When the user then sees timeouts in their logs, they can go look at the output of the orphan reporter and correlate certain properties that aid debugging in production. For example, if a single node is slow but the rest of the cluster is responsive, this would be visible from orphan reporting.

Configuring Orphaned Response Reporting

The orphaned response reporting is very similar in principle to the tracing threshold logging, but instead of tracking responses which are over a specific threshold it tracks those responses which are "orphaned".

The emitInterval and sampleSize can be adjusted, see the tracing orphaned logging options for details. They default to 10s and 128 samples per service, respectively. The overall structure looks like this (here prettified for readability):

{
  “<service-a>”: {
    “total_count”: 1234,
    “top_requests”: [{<entry>}, {<entry>},...]
  },
  “<service-b>”: {
    “total_count”: 1234,
    “top_requests”: [{<entry>}, {<entry>},...]
  },
}

The total_count represents the total amount of recorded items in each interval per service. The number of entries in “top_requests” is configured by the sampleSize. The service placeholder is replaced with each service, i.e. “kv”, “query” etc. Each entry looks like this, with all fields populated (same as the threshold logging):

{
  "total_duration_us": 1200,
  "encode_duration_us": 100,
  "last_dispatch_duration_us": 40,
  "total_dispatch_duration_us": 40,
  "last_server_duration_us": 2,
  “timeout_ms”: 75000,
  "operation_name": "upsert",
  "last_local_id": "66388CF5BFCF7522/18CC8791579B567C",
  "operation_id": "0x23",
  "last_local_socket": "10.211.55.3:52450",
  "last_remote_socket": "10.112.180.101:11210"
  "timeout_ms": 75000,
}

If a field is not present (because for example dispatch did not happen), it will not be included.