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tarantool-etcd-tzk Acked writes are not fsynced — shipped config.yaml has no wal section
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| Created by | Eugene Blikh |
| Owner | bigbes@gmail.com |
| Created | 2026-07-17T13:20:53Z |
| Updated | 2026-07-17T13:20:53Z |
etcd fdatasyncs the WAL before responding, so an acked write survives power loss. Our ack ORDERING is correct (box.commit() before the response — app/etcd/kv.lua:566-586, app/etcd/txn.lua:278-292), but the shipped config.yaml:30-34 has NO wal: section, so Tarantool defaults to wal_mode='write' (page cache, no fsync). An acked write survives a process crash but NOT power loss — weaker than etcd on the same wire ack. Telling detail: the bench harness explicitly sets WalMode="fsync" 'for symmetric durability' (tests/conformance/bench/benchharness/spawn.go:42-49). So our benchmarks measure fsync durability while the shipped default does not provide it. That asymmetry should be a decision, not an accident. Judgment call: arguably deployment config rather than a code gap — one line closes it. Filed so the choice is explicit either way.
Either wal.mode: fsync in config.yaml, or an explicit docs/TODO.md divergence stating the shipped default trades durability for throughput and why the bench harness differs.
No outgoing dependencies.
Nothing depends on this issue.
| id | tarantool-etcd-tzk |
| content_hash | 3118f9aa62633997a681d45e16a91f84bed91eb8b469c292c08f094d08840e0d |
| title | Acked writes are not fsynced — shipped config.yaml has no wal section |
| description | etcd fdatasyncs the WAL before responding, so an acked write survives power loss. Our ack ORDERING is correct (box.commit() before the response — app/etcd/kv.lua:566-586, app/etcd/txn.lua:278-292), but the shipped config.yaml:30-34 has NO wal: section, so Tarantool defaults to wal_mode='write' (page cache, no fsync). An acked write survives a process crash but NOT power loss — weaker than etcd on the same wire ack. Telling detail: the bench harness explicitly sets WalMode="fsync" 'for symmetric durability' (tests/conformance/bench/benchharness/spawn.go:42-49). So our benchmarks measure fsync durability while the shipped default does not provide it. That asymmetry should be a decision, not an accident. Judgment call: arguably deployment config rather than a code gap — one line closes it. Filed so the choice is explicit either way. |
| design | |
| acceptance_criteria | Either wal.mode: fsync in config.yaml, or an explicit docs/TODO.md divergence stating the shipped default trades durability for throughput and why the bench harness differs. |
| notes | |
| status | open |
| priority | 2 |
| issue_type | bug |
| assignee | NULL |
| estimated_minutes | NULL |
| created_at | 2026-07-17T13:20:53Z |
| created_by | Eugene Blikh |
| owner | bigbes@gmail.com |
| updated_at | 2026-07-17T13:20:53Z |
| closed_at | NULL |
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| external_ref | NULL |
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| compaction_level | 0 |
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| metadata | <binary> |
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| timeout_ns | 0 |
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| no_history | 0 |
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| issue_id | tarantool-etcd-tzk |
| label | etcd-changelog-sweep |
| id | 019f703c-aefa-7f23-8f17-8d0d098ddf0f |
| issue_id | tarantool-etcd-tzk |
| event_type | created |
| actor | Eugene Blikh |
| old_value | |
| new_value | |
| comment | NULL |
| created_at | 2026-07-17T16:20:52Z |
| id | 019f703c-aefb-7a31-8801-577c26cb2bec |
| issue_id | tarantool-etcd-tzk |
| event_type | label_added |
| actor | Eugene Blikh |
| old_value | NULL |
| new_value | NULL |
| comment | Added label: etcd-changelog-sweep |
| created_at | 2026-07-17T16:20:52Z |
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