Re-derivation of #23254 (@devsart95) on today's flush loop. The turn
flush in _flush_messages_to_session_db wrote one BEGIN IMMEDIATE
transaction per message row; a typical agent turn (user + assistant +
tool results) paid 3-8 transactions -- and, off WAL (the default on
macOS while the WAL-reset guard is active), 3-8 fsyncs -- per turn.
Adds SessionDB.append_messages_batch: same row shape as append_message
(shared _prepare_message_row serializer + _MESSAGE_INSERT_SQL column
list, so the two writers cannot drift), same compression-lock and
compression-closed guards, one aggregated session-counter UPDATE, one
transaction for the whole batch. Row serialization stays outside the
write lock.
The flush loop now collects the turn's new rows and writes them in one
call. All-or-nothing pairs exactly with the persisted-marker stamping:
on failure no rows landed and no markers were stamped, so the next
flush re-writes the whole tail (same recovery contract as before,
minus the partial-prefix case that could double-count).
Measured (same harness, 5-message turn, journal_mode=DELETE,
synchronous=FULL): 2.32ms -> 0.83ms median per turn flush (64% faster,
5 fsyncs -> 1). On WAL the win is smaller but the atomicity fix holds.
Three provably-safe optimizations for O(n)-per-iteration history walks:
1. sanitize_tool_call_arguments: optional identity-keyed cursor (strong
refs to the exact validated message objects) skips re-json.loads-ing
already-validated history each loop iteration. Any list rewrite
(compression, repair, undo, steer) breaks the identity prefix match
and forces re-scan from the divergence point. Wired via a per-agent
cursor dict in conversation_loop.
2. estimate_messages_tokens_rough: per-message memo keyed on a deep
identity fingerprint (strings pinned by strong reference so id()
aliasing is impossible; scalars by value; dicts/lists structurally
with key order). Equal fingerprints imply identical str(shadow)
bytes, hence identical estimates. Unfingerprintable shapes fall
through to direct compute. Bounded FIFO cache (4096 entries).
3. _flush_messages_to_session_db_unlocked: bounded scan that skips the
identity-matched prefix of the previous successful flush's snapshot.
Snapshot only taken on full success; cleared on exception. Compression
rewrites use fresh copies, breaking identity and forcing full re-scan.
Parity proven in tests/agent/test_cursor_optimizations_parity.py:
500-message synthetic histories with tool calls, malformed args, unicode,
element-wise old==new across 3 iterations incl. simulated compression.
Measured (median of 5): sanitize 0.097ms->0.011ms, tokens 1.145ms->0.853ms,
persist-scan 179.5us->10.0us at 500 messages.
devsart95
teknium1