fix(tracing): truncate long span attributes (#13270) [backport 2.21] (DO NOT MERGE)

[wantsui]

DO NOT MERGE

2.21 backport of: #13270

Truncate span resource name, tag key and tag values.

Previously, a very large resource name would result in a runtime error during encoding.

If any of these have over 25000 chars, this will truncate them to up to 2500 chars (and include the suffix <truncated>)
The agent will truncate based on the limits
here

Resolves:

• [BUG]: RuntimeError: failed to pack span for large SQL queries #13221

• Error inserting SQL statement into string table #6587

• PR author has checked that all the criteria below are met

• The PR description includes an overview of the change

• The PR description articulates the motivation for the change

• The change includes tests OR the PR description describes a testing strategy

• The PR description notes risks associated with the change, if any

• Newly-added code is easy to change

• The change follows the library release note guidelines

• The change includes or references documentation updates if necessary

• Backport labels are set (if applicable)

• Reviewer has checked that all the criteria below are met

• Title is accurate

• All changes are related to the pull request's stated goal

• Avoids breaking API changes

• Testing strategy adequately addresses listed risks

• Newly-added code is easy to change

• Release note makes sense to a user of the library

• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment

• Backport labels are set in a manner that is consistent with the release branch maintenance
  policy

---

(cherry picked from commit 5aa32d1)

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/truncate-long-span-attributes-a4900ee9844160b4.yaml  @DataDog/apm-python
tests/snapshots/tests.integration.test_integration_snapshots.test_encode_span_with_large_string_attributes[v0.4].json  @DataDog/apm-python
tests/snapshots/tests.integration.test_integration_snapshots.test_encode_span_with_large_string_attributes[v0.5].json  @DataDog/apm-python
ddtrace/_trace/_limits.py                                               @DataDog/apm-sdk-api-python
ddtrace/internal/_encoding.pyx                                          @DataDog/apm-core-python
tests/integration/test_integration.py                                   @DataDog/apm-core-python
tests/integration/test_integration_snapshots.py                         @DataDog/apm-core-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-27 22:42:13

Comparing candidate commit 12f9c78 in PR branch backport-13270-to-2.21 with baseline commit 7990c03 in branch 2.21.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 14 metrics, 0 unstable metrics.