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GeezerVison is showing github.com — [connectors] Release the Delta reader permit while paused by swanandx · Pull Request #7749 · feldera/feldera

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@swanandx

@swanandx swanandx commented Oct 30, 2026

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Linked Issue

Closes #7746

Describe Manual Test Plan

A paused Delta reader now gives up its reader permit until it resumes, so a connector that has voted to commit can no longer block one that has not. The repro from the issue now runs in catchup and always mode; both fail without the fix and pass with it.

Checklist

  • Unit tests added/updated
  • Integration tests added/updated
  • Documentation updated
  • Changelog updated

Breaking Changes?

Mark if you think the answer is yes for any of these components:

  • OpenAPI / REST HTTP API / feldera-types / manager (What is a breaking change?)
  • Feldera SQL (Syntax, Semantics)
  • feldera-sqllib (incl. dependencies fxp, etc.) (What is a breaking change?)
  • Python SDK (What is a breaking change?)
  • fda (CLI arguments)
  • Adapters (including configuration)
  • Storage Format / Checkpoints
  • Others (specify)

Describe Incompatible Changes

None.

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@swanandx
swanandx requested a review from ryzhyk October 30, 2026 18:14
ryzhyk
ryzhyk approved these changes Oct 30, 2026
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@swanandx
swanandx enabled auto-merge October 30, 2026 18:44
@mythical-fred-oss

mythical-fred-oss Bot commented Oct 30, 2026

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LGTM. The fix is narrow and correct. A paused reader now releases its DELTA_READER_SEMAPHORE permit while it waits in wait_running and acquires one again when it resumes. execute_df_inner is the only place that acquires the permit, so no other path can deadlock this way.

What I ran Result
cargo test -p static-connectors --test connector_suites paused_reader_holds_permit, debug build, 5 runs ✅ 2/2 every run
The same, with all 80 cores busy, 3 runs ✅ 2/2 every run (~43 s)
The same, release build (as CI runs it), 8 runs ✅ 2/2 every run (~4.6 s)
The same, with the input.rs change reverted ❌ both fail: "transaction did not commit within 60000 ms"
connector_suites integrated::delta_table::, release build ✅ 181 passed, 1 ignored
pre-commit run --files <changed files> ✅

Gates: the PR adds an integration test that fails without the fix. The test showed no flakiness in debug, release or loaded runs. It also has a guard (light_last < light_target) that names the cause if the deadlock setup ever fails to happen. The commit message is good. Nothing is user-visible, so no docs are needed.
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@swanandx @anandbraman
[connectors] Release the Delta reader permit while paused
ae7d172 
A paused Delta reader kept its reader permit. A connector that voted
to commit is not drained, so it stays paused, and a connector that
still needs a permit waits forever. Both catchup and always modes hang.

Co-authored-by: Anand Raman <[email protected]>
Signed-off-by: Swanand Mulay <[email protected]>
@swanandx
swanandx force-pushed the issue7746 branch from f730f8d to ae7d172 Compare October 30, 2026 18:57
@swanandx
swanandx disabled auto-merge October 30, 2026 19:08
@swanandx
swanandx added this pull request to the merge queue Oct 30, 2026
Merged via the queue into main with commit d0eac3f Oct 31, 2026
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@swanandx
swanandx deleted the issue7746 branch October 31, 2026 00:31
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@ryzhyk ryzhyk ryzhyk approved these changes

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[connectors] Delta catch-up transaction deadlocks when paused readers hold reader permits

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@swanandx @ryzhyk
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