File size: 9,429 Bytes
98938c3 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 | """SQLAlchemy-backed append-only ledger — a durable backend for the event store.
This is the same append-only ledger contract as the in-memory ``Ledger`` and the
``SQLiteLedger``, but persisted through SQLAlchemy 2.x so the *same* code drives a
hosted Postgres (Neon) event store and a local SQLite file. It is a backend for
the ledger, not a replacement: the ``Event`` envelope and the ``Ledger`` interface
are unchanged, and the append-only log remains the single source of truth (ADR-0014).
Design decisions (mirroring ``SQLiteLedger`` so it is a drop-in substitute):
- UNIQUE constraint on ``id`` enforces idempotency at the DB layer; a duplicate
insert is caught and ignored, so retried workers cannot double-write.
- A serial ``offset`` column gives a deterministic insertion order independent of
clock skew in ``created_at`` or duplicate ``turn`` values on retry.
- An in-memory cache mirrors the SQLite ledger: hot reads (``events``) hit the
cache; the DB is consulted for replay (``tail``) and on open (``from_file``).
- ``snapshot_to`` is backend-agnostic: it copies the log into a destination
ledger (default SQLite file), so a Postgres run snapshots to a portable file
that ``from_file`` can reopen — no vendor backup API required.
- ``reset`` clears the current run's events (matching ``SQLiteLedger`` semantics);
cross-run history is a separate concern.
SQLAlchemy is imported lazily inside ``__init__`` so that importing this module —
and therefore ``src.core.*`` — never requires SQLAlchemy or a database driver to be
installed. The offline in-memory path stays import-clean.
Backend selection lives in :mod:`src.core.ledger_factory`: with ``DATABASE_URL``
set the system uses this store; otherwise it uses the in-memory ``Ledger``.
"""
from __future__ import annotations
import json
from datetime import datetime, timezone
from pathlib import Path
from typing import TYPE_CHECKING, Any
from src.core.events import Event
from src.core.ledger import Ledger
if TYPE_CHECKING: # types only — never imported at runtime on the offline path
from sqlalchemy import Engine, MetaData, Table
def _normalise_url(url: str | Path) -> str:
"""Accept a SQLAlchemy URL or a bare filesystem path.
A value containing ``://`` is treated as a full SQLAlchemy URL (e.g.
``postgresql+psycopg://…`` or ``sqlite:///abs/path.db``). Anything else is
treated as a SQLite file path, including ``:memory:``.
"""
text = str(url)
if "://" in text:
return text
if text == ":memory:":
return "sqlite://"
return f"sqlite:///{text}"
class SqlAlchemyLedger(Ledger):
"""Persistent append-only ledger backed by SQLAlchemy (Postgres or SQLite).
Drop-in replacement for the in-memory ``Ledger`` with the same idempotency
guarantee, plus durable storage and snapshot/restore. Mirrors the public
surface of ``SQLiteLedger``: ``snapshot_to``, ``from_file``, ``tail``,
``latest_offset`` and ``close``.
"""
def __init__(self, url: str | Path = ":memory:") -> None:
# Lazy import: keeps src.core.* importable without SQLAlchemy installed.
from sqlalchemy import (
Column,
DateTime,
Integer,
MetaData,
String,
Table,
Text,
create_engine,
)
self._url = _normalise_url(url)
# pool_pre_ping keeps pooled Neon connections healthy across idle gaps;
# it is harmless for SQLite.
self._engine: Engine = create_engine(self._url, pool_pre_ping=True)
self._metadata: MetaData = MetaData()
self._events_table: Table = Table(
"events",
self._metadata,
Column("offset", Integer, primary_key=True, autoincrement=True),
Column("id", String(64), unique=True, nullable=False),
Column("run_id", String, nullable=False, index=True),
Column("turn", Integer, nullable=False),
Column("kind", String, nullable=False, index=True),
Column("actor", String, nullable=False, index=True),
Column("payload", Text, nullable=False),
Column("created_at", DateTime(timezone=True), nullable=False),
Column("schema_version", Integer, nullable=False, server_default="1"),
)
self._metadata.create_all(self._engine)
self._cache: list[Event] = []
self._seen_ids: set[str] = set()
self._load_cache()
# ── Ledger API ────────────────────────────────────────────────────────────
def append(self, event: Event) -> Event:
if event.id in self._seen_ids:
return event
from sqlalchemy.exc import IntegrityError
try:
with self._engine.begin() as conn:
conn.execute(
self._events_table.insert().values(
id=event.id,
run_id=event.run_id,
turn=event.turn,
kind=event.kind,
actor=event.actor,
payload=json.dumps(event.payload),
created_at=_aware(event.created_at),
schema_version=event.schema_version,
)
)
self._cache.append(event)
self._seen_ids.add(event.id)
except IntegrityError:
# Duplicate id inserted concurrently — idempotent, safe to ignore.
self._seen_ids.add(event.id)
return event
@property
def events(self) -> tuple[Event, ...]:
return tuple(self._cache)
def reset(self) -> None:
with self._engine.begin() as conn:
conn.execute(self._events_table.delete())
self._cache.clear()
self._seen_ids.clear()
# ── persistence helpers (parity with SQLiteLedger) ──────────────────────────
def snapshot_to(self, dest: str | Path) -> None:
"""Copy the full log into *dest* (a SQLAlchemy URL or SQLite path).
Backend-agnostic: unlike SQLite's native ``.backup()`` there is no portable
vendor API across Postgres and SQLite, so the snapshot is taken by replaying
the log into a fresh ledger at *dest*. The result is a standalone ledger
that ``from_file`` can reopen — typically a local SQLite file checkpointing
a Postgres run.
"""
target = SqlAlchemyLedger(dest)
target.reset()
target.extend(self._read_all())
target.close()
@classmethod
def from_file(cls, path: str | Path) -> "SqlAlchemyLedger":
"""Open an existing store (URL or SQLite path) and rehydrate the cache."""
return cls(path)
def tail(self, from_offset: int = 0) -> tuple[Event, ...]:
"""Return events with offset > *from_offset* (for crash-recovery replay)."""
from sqlalchemy import select
t = self._events_table
stmt = select(t).where(t.c.offset > from_offset).order_by(t.c.offset)
with self._engine.connect() as conn:
rows = conn.execute(stmt).mappings().all()
return tuple(self._row_to_event(row) for row in rows)
def latest_offset(self) -> int:
from sqlalchemy import func, select
stmt = select(func.max(self._events_table.c.offset))
with self._engine.connect() as conn:
value = conn.execute(stmt).scalar()
return value or 0
def close(self) -> None:
self._engine.dispose()
# ── internal ────────────────────────────────────────────────────────────────
def _load_cache(self) -> None:
for event in self._read_all():
self._cache.append(event)
self._seen_ids.add(event.id)
def _read_all(self) -> list[Event]:
from sqlalchemy import select
t = self._events_table
stmt = select(t).order_by(t.c.offset)
with self._engine.connect() as conn:
rows = conn.execute(stmt).mappings().all()
return [self._row_to_event(row) for row in rows]
@staticmethod
def _row_to_event(row: Any) -> Event:
created_at = row["created_at"]
if isinstance(created_at, str):
try:
created_at = datetime.fromisoformat(created_at)
except (ValueError, TypeError):
created_at = datetime.now(timezone.utc)
created_at = _aware(created_at)
payload = row["payload"]
if isinstance(payload, str):
payload = json.loads(payload)
return Event(
id=row["id"],
run_id=row["run_id"],
turn=row["turn"],
kind=row["kind"], # type: ignore[arg-type]
actor=row["actor"],
payload=payload,
created_at=created_at,
schema_version=row["schema_version"],
)
def _aware(dt: datetime) -> datetime:
"""Coerce a datetime to timezone-aware UTC (SQLite drops tzinfo on round-trip)."""
if dt.tzinfo is None:
return dt.replace(tzinfo=timezone.utc)
return dt
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