Dissect filter plugin

Fast, allocation-friendly alternative to grok for parsing logs that use fixed delimiters. Use dissect for predictable formats and fall back to grok only when you need regex flexibility.

• Package: logstash-filter-dissect
• Coverage source: default/bundled
• Official catalog entry: Yes

Plugin overview

dissect is used in the Logstash filter stage. Extracts structured fields from delimited text.

Typical use cases

• Tag failed operations and route them to dedicated troubleshooting views.
• Transform fields before indexing to keep schema and naming consistent.

Input and output behavior

• Flow: Tokenizes text by delimiters and writes deterministic captures to fields.
• Input: works on events that match your surrounding if conditions.
• Output: updates the current event in place unless configured otherwise.
• Important options: tag_on_failure, convert_datatype, mapping.
• Failure signaling: uses tag_on_failure (default: ["_dissectfailure"]) so failed events can be routed or inspected.

Options

Required

• No required plugin-specific options.

Optional

• convert_datatype (type: hash; default: {}) — Per-field type conversion applied after extraction (for example { "status" => "int" }).
• mapping (type: hash; default: {}) — Map of source field to dissect pattern (for example { "message" => "%{ts} %{+ts} %{level} %{msg}" }).
• tag_on_failure (type: array; default: ["_dissectfailure"]) — Tags applied when the dissect pattern does not match.

Example configuration

filter {
  dissect {
    mapping => {
      "message" => "%{ts} %{+ts} [%{level}] %{logger} - %{msg}"
    }
    convert_datatype => {
      "pid"    => "int"
      "status" => "int"
    }
    tag_on_failure => [ "_dissectfailure" ]
  }
}

Common options configuration

All Logstash filter plugins support these shared options:

• add_field (type: hash; default: {}) — Adds fields when the filter succeeds. Supports dynamic field names and values.
• add_tag (type: array; default: []) — Adds one or more tags when the filter succeeds.
• enable_metric (type: boolean; default: true) — Enables or disables metric collection for this plugin instance.
• id (type: string; default: none) — Sets an explicit plugin instance ID for monitoring and troubleshooting.
• periodic_flush (type: boolean; default: false) — Calls the filter flush method at regular intervals.
• remove_field (type: array; default: []) — Removes fields when the filter succeeds. Supports dynamic field names.
• remove_tag (type: array; default: []) — Removes tags when the filter succeeds.

filter {
  dissect {
    add_field => { "pipeline_stage" => "parsed" }
    add_tag => ["parsed", "logstash_filter"]
    enable_metric => true
    id => "my_filter_instance"
    periodic_flush => false
    remove_field => ["tmp_field"]
    remove_tag => ["temporary"]
  }
}

Apply in Logit.io

1. Open your stack in Logit.io and navigate to Logstash Pipelines.
2. In the filter { ... } section, add a dissect block.
3. Save your pipeline changes, then restart the Logstash pipeline if prompted.
4. Send sample events and verify parsed/enriched fields in OpenSearch Dashboards.

Validation checklist

• Confirm the dissect block compiles without syntax errors.
• Verify expected new/updated fields exist in sample documents.
• Verify unexpected fields are not removed unless explicitly configured.
• Confirm tags added on success/failure align with your alerting and routing rules.

Troubleshooting

• If events are unchanged, verify your filter condition (if ...) matches incoming events.
• If the pipeline fails to start, validate braces/quotes and retry with a minimal filter block.
• Check for tag_on_failure tags (default: ["_dissectfailure"]) to quickly isolate parse/mutation failures.
• If throughput drops, reduce expensive operations and test with representative sample volume.

References

• GitHub package: logstash-filter-dissect (opens in a new tab)
• Canonical catalog: /log-management/ingestion-pipeline/logstash-filters-reference