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https://issues.apache.org/jira/browse/FLINK-41265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18134075#comment-18134075
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Hao Yu commented on FLINK-41265:
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Please assign the issues to me, and I will attempt to resolve them.
> Add a metric for JSON messages with ignored parse errors
> --------------------------------------------------------
>
> Key: FLINK-41265
> URL: https://issues.apache.org/jira/browse/FLINK-41265
> Project: Flink
> Issue Type: Improvement
> Components: Formats (JSON, Avro, Parquet, ORC, SequenceFile),
> Runtime / Metrics
> Affects Versions: 2.3.0
> Reporter: Hao Yu
> Priority: Minor
>
> Problem
> When json.ignore-parse-errors is enabled, JSON parsing or field conversion
> errors can be ignored without a metric indicating how many input messages
> were affected.
> There are two relevant cases:
> - Invalid JSON causes a message to be skipped.
> - A field conversion fails and the field is set to null, while the remaining
> row is still emitted.
> For example, with an INT field named "id", the input \{"id":"abc"} may
> produce a row whose id is null. Counting only errors caught by the outer
> deserialization method would miss this case.
> Motivation
> In production, this option may have been enabled long before an incident, and
> the users investigating the issue may no longer be aware of it. The job
> continues running without failing, but some expected records are missing or
> some fields unexpectedly become null. Users may therefore suspect data loss
> in Flink, without realizing that parsing errors are being ignored according
> to the configured behavior.
> Users also need visibility into when invalid input starts appearing. A metric
> exposed on a monitoring dashboard would help them:
> - Identify when ignored parsing errors first occur.
> - Observe how their frequency changes over time.
> - Determine how long the problem persists and whether it is still ongoing.
> - Correlate the incident with upstream data or schema changes.
> - Configure alerts when ignored parsing errors occur or increase.
> The metric would make these errors observable while preserving the existing
> error-tolerant behavior.
> Proposed change
> Add a counter named numMessagesWithParseErrors to the plain JSON format,
> registered through DeserializationSchema.InitializationContext when
> json.ignore-parse-errors is enabled.
> The counter should:
> - Cover both the JsonNode and streaming JsonParser decoders.
> - Include ignored JSON parsing errors and ignored field conversion errors.
> - Increment at most once per input message, even if multiple fields fail.
> - Treat a top-level JSON array as one input message, regardless of how many
> rows it produces.
> - Exclude accepted null field values, permitted missing fields, and empty
> inputs that do not cause parsing exceptions.
> - Preserve existing deserialization behavior.
> The counter represents affected input messages, including messages that still
> produce rows with null fields. It should not be interpreted as the number of
> dropped output rows.
> Scope
> This issue covers the plain JSON format.
> CDC formats and connector-specific metric context changes are outside its
> scope. File-source metric reporting and Kafka key/value metric-group
> isolation require separate follow-ups.
> Related work
> FLINK-20789 tracks the broader request for metrics in formats supporting
> ignore-parse-errors. This issue proposes the JSON-specific implementation.
> https://issues.apache.org/jira/browse/FLINK-20789
> FLINK-38819 added logging for ignored JSON parsing errors. This proposal adds
> a counter that can be used directly by monitoring dashboards and alerts.
> https://issues.apache.org/jira/browse/FLINK-38819
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