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tarantool-etcd-vnp Watch/Range reject compact_revision itself — off-by-one vs etcd, livelocks watch recovery
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| Created by | Eugene Blikh |
| Owner | bigbes@gmail.com |
| Created | 2026-07-17T13:18:41Z |
| Updated | 2026-07-17T13:18:41Z |
etcd keeps the tombstone whose revision == the compact revision and rejects only rev < compactMainRev (verified at server/storage/mvcc/kvstore_txn.go:80 — 'if rev < tr.s.compactMainRev'). A watch or range started exactly AT compact_revision succeeds. We reject at <= on both paths and delete the boundary row outright: - app/etcd/compact.lua:63-84 — the batch loop breaks on 'tuple.mod_revision > target_rev', so it deletes every kv_history row with mod_revision <= target_rev, INCLUDING the entry at target_rev. - app/etcd/watch.lua:281 — 'if opts.start_revision <= compacted then return errors.revision_compacted(compacted)' - app/etcd/kv.lua:261 — 'if target_rev <= compacted then error(errors.revision_compacted())' Why this is more than cosmetic: etcd's documented watch-recovery pattern is 'on a canceled response carrying compact_revision, restart the watch at compact_revision'. Against this server that revision is itself rejected, so a conforming clientv3 watcher that survives a compaction retries forever against the same rejection — an infinite cancel loop. Verified by hand (not just by the sweep agent) against both our source and the upstream clone.
Two coupled changes; do them together or the boundary stays inconsistent: (1) compaction must retain rows with mod_revision == target_rev — break the loop on '>=' rather than deleting through the boundary; (2) both guards move from '<=' to '<'. Note the retained boundary row must be the tombstone/latest version at that revision, matching etcd's key_index.go behavior of keeping the generation's last entry.
Compact(N) then Watch(start_revision=N) succeeds and delivers the event at N, matching etcd; Range(revision=N) after Compact(N) succeeds; a conformance test probes the compact-revision boundary itself on both backends (current compact_test.go only probes strictly below it); clientv3 restart-at-CompactRevision terminates.
No outgoing dependencies.
Nothing depends on this issue.
| id | tarantool-etcd-vnp |
| content_hash | 1d9a61e1b6a987a8cb6ddae9833f7073ce29f05f3b852205dae442bfa24f3819 |
| title | Watch/Range reject compact_revision itself — off-by-one vs etcd, livelocks watch recovery |
| description | etcd keeps the tombstone whose revision == the compact revision and rejects only rev < compactMainRev (verified at server/storage/mvcc/kvstore_txn.go:80 — 'if rev < tr.s.compactMainRev'). A watch or range started exactly AT compact_revision succeeds. We reject at <= on both paths and delete the boundary row outright: - app/etcd/compact.lua:63-84 — the batch loop breaks on 'tuple.mod_revision > target_rev', so it deletes every kv_history row with mod_revision <= target_rev, INCLUDING the entry at target_rev. - app/etcd/watch.lua:281 — 'if opts.start_revision <= compacted then return errors.revision_compacted(compacted)' - app/etcd/kv.lua:261 — 'if target_rev <= compacted then error(errors.revision_compacted())' Why this is more than cosmetic: etcd's documented watch-recovery pattern is 'on a canceled response carrying compact_revision, restart the watch at compact_revision'. Against this server that revision is itself rejected, so a conforming clientv3 watcher that survives a compaction retries forever against the same rejection — an infinite cancel loop. Verified by hand (not just by the sweep agent) against both our source and the upstream clone. |
| design | Two coupled changes; do them together or the boundary stays inconsistent: (1) compaction must retain rows with mod_revision == target_rev — break the loop on '>=' rather than deleting through the boundary; (2) both guards move from '<=' to '<'. Note the retained boundary row must be the tombstone/latest version at that revision, matching etcd's key_index.go behavior of keeping the generation's last entry. |
| acceptance_criteria | Compact(N) then Watch(start_revision=N) succeeds and delivers the event at N, matching etcd; Range(revision=N) after Compact(N) succeeds; a conformance test probes the compact-revision boundary itself on both backends (current compact_test.go only probes strictly below it); clientv3 restart-at-CompactRevision terminates. |
| notes | |
| status | open |
| priority | 0 |
| issue_type | bug |
| assignee | NULL |
| estimated_minutes | NULL |
| created_at | 2026-07-17T13:18:41Z |
| created_by | Eugene Blikh |
| owner | bigbes@gmail.com |
| updated_at | 2026-07-17T13:18:41Z |
| closed_at | NULL |
| closed_by_session | |
| external_ref | NULL |
| spec_id | |
| compaction_level | 0 |
| compacted_at | NULL |
| compacted_at_commit | NULL |
| original_size | NULL |
| sender | |
| ephemeral | 0 |
| wisp_type | |
| pinned | 0 |
| is_template | 0 |
| mol_type | |
| work_type | |
| source_system | |
| metadata | <binary> |
| source_repo | |
| close_reason | |
| event_kind | |
| actor | |
| target | |
| payload | |
| await_type | |
| await_id | |
| timeout_ns | 0 |
| waiters | |
| hook_bead | |
| role_bead | |
| agent_state | |
| last_activity | NULL |
| role_type | |
| rig | |
| due_at | NULL |
| defer_until | NULL |
| no_history | 0 |
| started_at | NULL |
| is_blocked | 0 |
| issue_id | tarantool-etcd-vnp |
| label | etcd-changelog-sweep |
| id | 019f703a-ac96-7ce8-bc76-b40bfb3065d8 |
| issue_id | tarantool-etcd-vnp |
| event_type | created |
| actor | Eugene Blikh |
| old_value | |
| new_value | |
| comment | NULL |
| created_at | 2026-07-17T16:18:41Z |
| id | 019f703a-ac97-7add-9250-528204146424 |
| issue_id | tarantool-etcd-vnp |
| event_type | label_added |
| actor | Eugene Blikh |
| old_value | NULL |
| new_value | NULL |
| comment | Added label: etcd-changelog-sweep |
| created_at | 2026-07-17T16:18:41Z |
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