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Add an option to limit length of values of attributes and metric values #1130

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Add an option to limit length of values of attributes and metric values #1130

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4507656
Add an option to limit span attribute length
jtmalinowski Oct 22, 2020
deca25b
Change default value of OTEL_SPAN_ATTRIBUTE_SIZE_LIMIT to empty
jtmalinowski Oct 22, 2020
748eae0
Fix wording in Span attribute limiting section
jtmalinowski Oct 22, 2020
e7e54b3
Introduce metric label value size limit
jtmalinowski Oct 23, 2020
10af7ba
Spec compliance for truncating metric label values
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ed9bc5f
Limits docs improvements
jtmalinowski Oct 23, 2020
dabb292
Fix traces limiting requirement
jtmalinowski Oct 26, 2020
4102464
Expand span attribute limits to all attributes
jtmalinowski Oct 27, 2020
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Merge remote-tracking branch 'upstream/master' into feature/span-attr…
jtmalinowski Oct 27, 2020
c175613
Wording improvements
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5259377
More accurate naming for attribute truncation env variables
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Merge remote-tracking branch 'upstream/main' into feature/span-attrib…
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Merge remote-tracking branch 'upstream/main' into feature/span-attrib…
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fix: typos
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fix: merge mistakes
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fix: PR feedback
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fix: typo in link
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fix: PR feedback
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fix: PR feedback
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chore: changelog
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Update specification/sdk-environment-variables.md
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Update specification/common/common.md
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fix: clarify priority of limits
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Merge branch 'main' into feature/span-attribute-size-limit
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fix: nerf logging requirements
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fix: grammar
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Fixes from Yuri
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fix: clarify metrics exemption
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fix: link
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fix: language
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Merge branch 'main' into feature/span-attribute-size-limit
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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -11,6 +11,10 @@ release.

### Traces

- Add generalized attribute count and attribute value length limits and relevant
environment variables.
([#1130](https:/open-telemetry/opentelemetry-specification/pull/1130))

### Metrics

### Logs
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4 changes: 4 additions & 0 deletions spec-compliance-matrix.md
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Expand Up @@ -79,6 +79,7 @@ formats is required. Implementing more than one format is optional.
| [IdGenerators](specification/trace/sdk.md#id-generators) | | + | + | | + | + | | | + | + | | + |
| [SpanLimits](specification/trace/sdk.md#span-limits) | X | + | + | | + | + | | | | - | | + |
| [Built-in `SpanProcessor`s implement `ForceFlush` spec](specification/trace/sdk.md#forceflush-1) | | | | | + | + | | | + | + | | |
| [Attribute Limits](specification/common/common.md#attribute-limits) | X | | | | | | | | | | | |

## Baggage

Expand Down Expand Up @@ -141,10 +142,13 @@ Note: Support for environment variables is optional.
|OTEL_TRACES_EXPORTER | - | + | | + | + | + | | - | - | | |
|OTEL_METRICS_EXPORTER | - | + | | + | - | - | | - | - | - | - |
|OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT | - | + | | + | + | - | | + | - | | |
|OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT | | | | | | | | | | | |
|OTEL_SPAN_EVENT_COUNT_LIMIT | - | + | | + | + | - | | + | - | | |
|OTEL_SPAN_LINK_COUNT_LIMIT | - | + | | + | + | - | | + | - | | |
|OTEL_TRACES_SAMPLER | - | + | | + | + | + | | - | - | | |
|OTEL_TRACES_SAMPLER_ARG | - | + | | + | + | + | | - | - | | |
|OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT | | | | | | | | | | | |
|OTEL_ATTRIBUTE_COUNT_LIMIT | | | | | | | | | | | |

## Exporters

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40 changes: 39 additions & 1 deletion specification/common/common.md
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Expand Up @@ -8,6 +8,7 @@ Table of Contents
</summary>

- [Attributes](#attributes)
- [Attribute Limits](#attribute-limits)

</details>

Expand Down Expand Up @@ -40,4 +41,41 @@ indices that are kept in sync (e.g., two attributes `header_keys` and `header_va
both containing an array of strings to represent a mapping
`header_keys[i] -> header_values[i]`).

See [Attribute and Label Naming](attribute-and-label-naming.md) for naming guidelines.
### Attribute Limits

Execution of erroneous code can result in unintended attributes. If there is no
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limits placed on attributes, they can quickly exhaust available memory, resulting
in crashes that are difficult to recover from safely.

By default an SDK SHOULD apply truncation as per the list of
[configurable parameters](#attribute-limits-configuration) below.

If an SDK provides a way to:

- set an attribute value length limit and the limit is set, then for each
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attribute value:
- if it is a string, if it exceeds that limit (counting any character in it as
1), SDK Spans MUST truncate that value, so that its length is at most equal
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to the limit,
- if it is an array of strings, then apply the above rule to each of the
values separately,
- otherwise a value MUST NOT be truncated;
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- set a limit of unique attribute keys, and the limit is set:
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- for each unique attributes key, addition of which would result in exceeding
the limit, SDK MUST discard that key/value pair.

There SHOULD be a log emitted to indicate to the user that an attribute was
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I agree with the sentiment of this paragraph -- we should tell the user when we discard or modify their telemetry data and we should be careful not to overwhelm a telemetry collection system by providing too many error messages about bad data.

This, to me, is the wrong place to specify error handling behavior. I'd like to see statements about error handling in general in the library guidelines part of the specification. For errors like this which may occur as a result of user data, I typically configure them to print once per minute or so. I believe we should use metrics to count occurrences of excessive metric value length and/or count.

Both of these outputs, logs and/or metrics about these events, are a form of "meta" telemetry, and the specification's SDK guidelines should say we aim to (1) do this well, (2) at low cost. For meta-telemetry logs this means once rarely per log statement, for metrics this means a requirement to have low cardinality, for example.

I propose removing this paragraph and filing an issue to update the library guidelines with general guidance on handling errors of this nature.

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@jtmalinowski jtmalinowski Jul 2, 2021 •
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@jmacd Given that this is in line with existing spec here https:/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#span-limits, do you think we could leave the paragraph as is, create the issue, and once we reach a consensus, I'll create a PR which will address this?

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@jmacd please feel free to amend the issue #1787 if you'd like to describe the problem in a different way

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@jmacd does the above work for you?

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Yes.

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I think solving this issue with logging is not the ideal solution. It assumes that logging is always available, which is not always the case - many languages have no standard log framework, and even if they do, using std log is not always what the rest of the application is using. In other words, logger must always be treated as a dependency, which may or may not be available.

In addition, the throttling of the logs effectively requires keeping a state per span. So why not report truncations as part of the span itself?

Regarding #1787, why not leave this paragraph out of this PR until an agreement on #1787 is reached? We are changing the spec, after all, it's better to leave the behavior unspecified than to change it.

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@jtmalinowski jtmalinowski Jul 17, 2021 •
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@yurishkuro I have changed "SHOULD" to "SHOULD NOT" to satisfy this criteria:

  • your ask to not prescribe a solution
  • don't immediately invalidate existing solutions, which may already be logging
  • don't make it hard for implementors in case they really needed to log (until we have a prescribed solution)

This isn't exactly what you asked for, but I think it does the job.

EDIT: Also, I'd appreciate if you double posted these comments about logging on the issue, otherwise it'll be hard to make any progress there.

truncated or discarded. To prevent excessive logging, the log MUST NOT be
emitted more than once per record on which an attribute is set. If a record is
embedded in another record (e.g. Events within a Span), then the log SHOULD NOT
be emitted more than once per parent record.

If the SDK implements the limits above, it MUST provide a way to change these
limits programmatically. Names of the configuration options SHOULD be the same as
in the list below.

<a name="attribute-limits-configuration"></a>
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**Configurable parameters:**

* `AttributeCountLimit` (Default=128) - Maximum allowed attribute count per record;
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* `AttributeValueLengthLimit` (Default=Infinity) - Maximum allowed attribute value length;
7 changes: 7 additions & 0 deletions specification/metrics/sdk.md
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Expand Up @@ -23,6 +23,7 @@ Table of Contents
</summary>

* [MeterProvider](#meterprovider)
* [Measurement Limits](#measurement-limits)
* [MeasurementProcessor](#measurementprocessor)
* [MetricProcessor](#metricprocessor)
* [MetricExporter](#metricexporter)
Expand All @@ -40,6 +41,12 @@ TODO:
* Configure timing (related to [issue
1432](https:/open-telemetry/opentelemetry-specification/issues/1432)).

## Measurement Limits

Measurement attributes are exempt from the
[common rules of attribute limits](../common/common.md#attribute-limits) due to
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It's confusing to have this here and not in the common section.

the experimental status of the Metrics SDK specification.
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I don't think this is true.

Our data model is stable and in it, the attributes contribute to the identity of a metric. If we truncate attributes we need to denote how that changes the identity of the point.

I'm not sure the SDK exiting experimental status will change this point


## MeasurementProcessor

`MeasurementProcessor` is an interface which allows hooks when a
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31 changes: 25 additions & 6 deletions specification/sdk-environment-variables.md
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Expand Up @@ -72,17 +72,36 @@ Depending on the value of `OTEL_TRACES_SAMPLER`, `OTEL_TRACES_SAMPLER_ARG` may b
| OTEL_BSP_MAX_QUEUE_SIZE | Maximum queue size | 2048 | |
| OTEL_BSP_MAX_EXPORT_BATCH_SIZE | Maximum batch size | 512 | Must be less than or equal to OTEL_BSP_MAX_QUEUE_SIZE |

## Span Collection Limits
## Attribute Limits

See the SDK [Attribute Limits](common/common.md#attribute-limits) section for the definition of the limits.

If an SDK does not implement truncation mechanism for all implementations of
attributes, then it SHOULD NOT offer an unscoped (e.g.
`OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT`, as opposed to scoped, e.g.
`OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT`) global environment variable for such a
limit. SDKs SHOULD only offer environment variables for the types of attributes,
for which that SDK implements truncation mechanism. For each implemented limit
SDK MUST first try to use the unscoped variable, if it isn't set, only then try
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to use the scoped variable.

| Name | Description | Default | Notes |
| --------------------------------- | ------------------------------------ | ------- | ----- |
| OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT | Maximum allowed attribute value size | | Empty value is treated as infinity. Non-integer and negative values are invalid. |
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| OTEL_ATTRIBUTE_COUNT_LIMIT | Maximum allowed span attribute count | 128 | |
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What is the diff with OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT?

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@jtmalinowski jtmalinowski Jul 6, 2021 •
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Applies to all attributes, except Metrics (temporarily exempted due to experimental status), so effectively that (for now) means spans and events. EDIT: also resources

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Before we go ahead: how does this interact with the rest of the related environment variables? What if the user sets OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT and also OTEL_ATTRIBUTE_COUNT_LIMIT? I'm guessing what you expect here, but it's not clarified anywhere.

For what is worth, if you remove this, we can totally merge this (and have this single environment variable done as a follow up, etc).

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So previously there was a paragraph about this in sdk-environment-variables, but there was an error in one of the sentences, and because it also applies to programmatic configuration, I moved that paragraph here https:/open-telemetry/opentelemetry-specification/pull/1130/files#diff-500cb43b9725373c25ea03660c293e59681e6e2f6ba3eb588188ed3b83dcbdcdR79.

I hope the wording is clear and we can merge.


## Span Limits <a name="span-collection-limits"></a>

**Status**: [Stable](document-status.md)

See the SDK [Span Limits](trace/sdk.md#span-limits) section for the definition of the limits.

| Name | Description | Default | Notes |
| ------------------------------- | ------------------------------------ | ------- | ----- |
| OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT | Maximum allowed span attribute count | 128 | |
| OTEL_SPAN_EVENT_COUNT_LIMIT | Maximum allowed span event count | 128 | |
| OTEL_SPAN_LINK_COUNT_LIMIT | Maximum allowed span link count | 128 | |
| Name | Description | Default | Notes |
| -------------------------------------- | ------------------------------------ | ------- | ----- |
| OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT | Maximum allowed attribute value size | | Empty value is treated as infinity. Non-integer and negative values are invalid. |
| OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT | Maximum allowed span attribute count | 128 | |
| OTEL_SPAN_EVENT_COUNT_LIMIT | Maximum allowed span event count | 128 | |
| OTEL_SPAN_LINK_COUNT_LIMIT | Maximum allowed span link count | 128 | |

## OTLP Exporter

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14 changes: 5 additions & 9 deletions specification/trace/sdk.md
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Expand Up @@ -319,20 +319,16 @@ Optional parameters:

## Span Limits

Erroneous code can add unintended attributes, events, and links to a span. If
these collections are unbounded, they can quickly exhaust available memory,
resulting in crashes that are difficult to recover from safely.
Span attributes MUST adhere to the [common rules of attribute limits](../common/common.md#attribute-limits).

To protect against such errors, SDK Spans MAY discard attributes, links, and
events that would increase the number of elements of each collection beyond
the configured limit.
SDK Spans MAY also discard links and events that would increase the number of
elements of each collection beyond the configured limit.

If the SDK implements the limits above it MUST provide a way to change these
limits, via a configuration to the TracerProvider, by allowing users to
configure individual limits like in the Java example bellow.

The name of the configuration options SHOULD be `AttributeCountLimit`,
`EventCountLimit` and `LinkCountLimit`. The options MAY be bundled in a class,
The name of the configuration options SHOULD be `EventCountLimit` and `LinkCountLimit`. The options MAY be bundled in a class,
which then SHOULD be called `SpanLimits`. Implementations MAY provide additional
configuration such as `AttributePerEventCountLimit` and `AttributePerLinkCountLimit`.
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Expand All @@ -350,7 +346,7 @@ public final class SpanLimits {

**Configurable parameters:**

* `AttributeCountLimit` (Default=128) - Maximum allowed span attribute count;
* [all common options applicable to attributes](../common/common.md#attribute-limits-configuration)
* `EventCountLimit` (Default=128) - Maximum allowed span event count;
* `LinkCountLimit` (Default=128) - Maximum allowed span link count;
* `AttributePerEventCountLimit` (Default=128) - Maximum allowed attribute per span event count;
Expand Down