What causes "write back id to db: %w" in nektos/act?

Treat the cache entry as not saved: rerun the workflow after clearing lock contention (stop duplicate act runs)

write back id to db: %w

Error message

write back id to db: %w

What it means

After inserting a cache record, insertCache immediately re-Updates it with bolthold.NextSequence()'s value written back into the record (so the ID field matches the bolt key). This error means the insert succeeded but the follow-up update transaction failed — leaving a half-initialized entry that lookups may not match. Same root causes as insert: lock contention, disk full, corruption.

Source

Thrown at pkg/artifactcache/handler.go:412

				And("Complete").Eq(true).
				SortBy("CreatedAt").Reverse()); err != nil {
			if errors.Is(err, bolthold.ErrNotFound) {
				continue
			}
			return nil, fmt.Errorf("find cache: %w", err)
		}
		return cache, nil
	}
	return nil, nil
}

func insertCache(db *bolthold.Store, cache *Cache) error {
	if err := db.Insert(bolthold.NextSequence(), cache); err != nil {
		return fmt.Errorf("insert cache: %w", err)
	}
	// write back id to db
	if err := db.Update(cache.ID, cache); err != nil {
		return fmt.Errorf("write back id to db: %w", err)
	}
	return nil
}

func (h *Handler) useCache(id uint64) {
	db, err := h.openDB()
	if err != nil {
		return
	}
	defer db.Close()
	cache := &Cache{}
	if err := db.Get(id, cache); err != nil {
		return
	}
	cache.UsedAt = time.Now().Unix()
	_ = db.Update(cache.ID, cache)
}

View on GitHub (pinned to 4f41128141)

Solutions

Treat the cache entry as not saved: rerun the workflow after clearing lock contention (stop duplicate act runs)
Free disk space on the cache volume
Delete the cache DB if a torn record makes the error repeat
Run cache-heavy matrix jobs with fewer parallel shards

Defensive patterns

Strategy: try-catch

Try / catch

if err := insertCache(db, cache); err != nil {
    if strings.Contains(err.Error(), "write back id") {
        // entry partially persisted; remove it to avoid a torn record
        _ = db.Delete(cache.ID, cache)
    }
    log.Warnf("cache save failed: %v", err)
}

Prevention

Treat insert+write-back as one logical unit; clean up on failure
Avoid concurrent cache saves to the same store
Clear the DB if torn records cause repeat failures

When it happens

Trigger: The two-step insert+update in insertCache (handler.go:406) racing with another writer, or hitting ENOSPC between the insert and update transactions.

Common situations: Concurrent cache saves from parallel matrix jobs through one cache server; low-disk CI runners; act crashed between the two transactions on a previous run.

Related errors

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/7cfa29d5f5794aa9. Report an issue: GitHub.