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fix(engine): force-delete in __run__ sweep for concurrency safety

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`migrate_v2_to_v3` ran `Dataset::delete_branch` (= `branches().delete(.., false)`),
which errors "BranchContents not found" if the branch is already gone. Since the
sweep now runs in `Omnigraph::open(ReadWrite)`, two processes opening the same
legacy v2 graph concurrently would race: one wins each delete, the other's open
fails. The migration only claimed idempotency under *sequential* retry.

Switch to `Dataset::force_delete_branch` (= `delete(.., true)`), Lance's
documented path for cleaning up zombie branches, which tolerates an
already-absent branch. The sweep is now idempotent under concurrent runners and
robust to partial/zombie state. Found in self-review; no behavior change for the
common single-open path.
This commit is contained in:
Ragnor Comerford 2026-05-31 16:20:45 +02:00
parent f6515073bf
commit 1c83377d77
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1 changed files with 10 additions and 4 deletions
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14
crates/omnigraph/src/db/manifest/migrations.rs
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@ -144,9 +144,10 @@ async fn migrate_v1_to_v2(dataset: &mut Dataset) -> Result<()> {
/// working after the `run_registry` module (the guard) is deleted, so it does
/// not depend on it.
///
/// Idempotent under retry: each run re-enumerates `list_branches` fresh, so a
/// crash before the stamp bump simply re-deletes whatever `__run__*` branches
/// still remain on the next open.
/// Idempotent under both sequential retry and concurrent runners: each run
/// re-enumerates `list_branches` fresh, and `force_delete_branch` tolerates a
/// branch that is already gone — so a crash before the stamp bump, or a second
/// process opening the same legacy graph at the same time, never errors out.
async fn migrate_v2_to_v3(dataset: &mut Dataset) -> Result<()> {
const LEGACY_RUN_BRANCH_PREFIX: &str = "__run__";
let branches = dataset
@ -161,8 +162,13 @@ async fn migrate_v2_to_v3(dataset: &mut Dataset) -> Result<()> {
})
.collect();
for name in run_branches {
// `force_delete_branch` deletes even when the `BranchContents` is
// already gone. Plain `delete_branch` errors "BranchContents not
// found", which would fail a second concurrent open (or a retry that
// raced another runner) after the first one swept the branch. Force is
// exactly Lance's documented path for cleaning up zombie branches.
dataset
.delete_branch(&name)
.force_delete_branch(&name)
.await
.map_err(|e| OmniError::Lance(e.to_string()))?;
}