# zodb-pgjsonb

> ZODB storage adapter for PostgreSQL using JSONB, powered by zodb-json-codec (Rust).

zodb-pgjsonb stores ZODB object state as queryable PostgreSQL JSONB instead of opaque
pickle bytea blobs. It uses the Rust-based zodb-json-codec library for transparent
pickle-to-JSON transcoding. ZODB sees pickle bytes at its boundaries; PostgreSQL sees
queryable JSON internally.

## Key Facts

- Package: zodb-pgjsonb
- License: ZPL-2.1
- Python: 3.12+
- PostgreSQL: 15+ (tested with 17; SQL features only require 9.5+)
- Codec: zodb-json-codec (Rust/PyO3, installed automatically)
- Repository: https://github.com/bluedynamics/zodb-pgjsonb

## ZODB Interfaces Implemented

- IStorage — core load/store/pack
- IMVCCStorage — per-connection MVCC instances
- IBlobStorage — tiered blobs (PG bytea + optional S3)
- IStorageUndoable — undo support in history-preserving mode
- IStorageIteration — transaction/record iteration
- IStorageRestoreable — zodbconvert migration support

## Architecture

```
ZODB.DB
  └→ PGJsonbStorage (main, factory, owns schema + pool)
       ├→ new_instance() → PGJsonbStorageInstance (per-connection, MVCC)
       ├→ zodb-json-codec    (pickle ↔ JSONB transcoding, Rust, GIL-free)
       ├→ psycopg3           (sync, pipelined writes, connection pool)
       ├→ LISTEN/NOTIFY      (instant invalidation via PG trigger)
       ├→ Tiered blobs       (PG bytea + optional S3 via zodb-s3blobs)
       └→ Pure SQL pack/GC   (recursive CTE on pre-extracted refs column)
```

### Write Path

1. ZODB calls `store(oid, serial, pickle_bytes, version, transaction)`
2. `zodb_json_codec.decode_zodb_record_for_pg_json()` transcodes pickle to JSON string (entirely in Rust, GIL released)
3. Class module/name extracted from `@cls` marker, state from `@s`, refs from `@ref` markers
4. State processors (plugins) run: pop keys from state, return extra column data
5. `tpc_vote()` batch-writes all objects via `executemany()` (pipelined, single round-trip)
6. `tpc_finish()` commits PG transaction, triggers NOTIFY for invalidation

### Read Path

1. ZODB calls `load(oid)` → check LRU cache first
2. Cache miss: `SELECT class_mod, class_name, state FROM object_state WHERE zoid = %s`
3. `zodb_json_codec.encode_zodb_record()` transcodes JSON back to pickle bytes (Rust)
4. Returns `(pickle_bytes, tid_bytes)` to ZODB

### MVCC

- `PGJsonbStorage.new_instance()` returns a `PGJsonbStorageInstance` per ZODB Connection
- Each instance uses `REPEATABLE READ` snapshot isolation for consistent reads
- `poll_invalidations()` starts snapshot FIRST, then queries invalidated OIDs
- TID generation uses PostgreSQL advisory locks for serialization
- Invalidation via LISTEN/NOTIFY (~1ms latency vs 1-5s polling in RelStorage)

### Pack Algorithm

Pure SQL — no object loading needed:

```sql
WITH RECURSIVE reachable AS (
    SELECT zoid FROM object_state WHERE zoid = 0
    UNION
    SELECT unnest(o.refs)
    FROM object_state o JOIN reachable r ON o.zoid = r.zoid
)
DELETE FROM object_state WHERE zoid NOT IN (SELECT zoid FROM reachable)
```

Pre-extracted `refs BIGINT[]` column enables 15-28x faster pack than RelStorage.

## Database Schema

### History-Free Mode (default)

```sql
object_state (
    zoid       BIGINT PRIMARY KEY,
    tid        BIGINT NOT NULL,
    class_mod  TEXT,
    class_name TEXT,
    state      JSONB,
    state_size INTEGER,
    refs       BIGINT[] DEFAULT '{}'
)

transaction_log (
    tid         BIGINT PRIMARY KEY,
    username    BYTEA,
    description BYTEA,
    extension   BYTEA
)

blob_state (
    zoid      BIGINT NOT NULL,
    tid       BIGINT NOT NULL,
    blob_size BIGINT NOT NULL,
    data      BYTEA,       -- NULL if in S3
    s3_key    TEXT,         -- NULL if in PG
    PRIMARY KEY (zoid, tid)
)
```

Indexes: `(class_mod, class_name)`, `GIN(refs)`, `(tid, zoid)`.

### History-Preserving Mode (additions)

```sql
object_history (
    zoid       BIGINT NOT NULL,
    tid        BIGINT NOT NULL,
    class_mod  TEXT,
    class_name TEXT,
    state      JSONB,
    state_size INTEGER,
    refs       BIGINT[] DEFAULT '{}',
    PRIMARY KEY (zoid, tid)
)

pack_state (zoid BIGINT PRIMARY KEY, tid BIGINT NOT NULL)
```

Uses copy-before-overwrite model: only previous versions archived before overwrite.

## Blob Storage

Three deployment modes:

| Mode | Configuration | Behavior |
|---|---|---|
| PG-only | No S3 keys | All blobs in PostgreSQL bytea |
| Tiered | S3 keys + blob-threshold | Small in PG, large in S3 |
| S3-only | S3 keys + blob-threshold=0 | All blobs in S3 |

Default threshold: 100KB. Local blob cache available for S3 mode.

Blob files use deterministic names: `{oid:016x}-{tid:016x}.blob`.

## History Modes

Both modes supported, convertible at runtime:

- **History-free** (default): Current state only, lower storage overhead
- **History-preserving**: Full revision history, undo support, undoLog/undoInfo

Conversion methods: `convert_to_history_free()`, `convert_to_history_preserving()`.
HP→HF is irreversible (drops all history).

## State Processor Plugins

Downstream packages can register processors that extract extra columns written
atomically alongside object state:

```python
@dataclasses.dataclass
class ExtraColumn:
    name: str              # SQL column name
    value_expr: str        # SQL expression for INSERT
    update_expr: str | None  # Optional ON CONFLICT expression

class IStateProcessor:
    def get_extra_columns(self) -> list[ExtraColumn]: ...
    def process(self, zoid, class_mod, class_name, state) -> dict | None: ...
    def get_schema_sql(self) -> str | None: ...   # Optional DDL
    def finalize(self, cursor) -> None: ...        # Optional post-vote hook
```

Used by plone-pgcatalog to write catalog index columns in the same PG transaction.

Processor `get_schema_sql()` DDL and `defer_startup_action()` callables run from
the first write transaction under a session-level advisory lock. A double-checked
schema-version gate (markers in `pgjsonb_schema_state`) lets replicas skip the
lock when their tagged DDL is already current: the static DDL block is auto-tagged
by `sha256`, deferred actions pass an explicit `version`, and `version=None` always
runs. `ZODB_PGJSONB_FORCE_DDL=1` forces a full re-apply.

## Configuration (ZConfig)

```xml
%import zodb_pgjsonb

<zodb_db main>
  <pgjsonb>
    dsn postgresql://user:pass@localhost:5432/zodb
    history-preserving false
    pool-size 1
    pool-max-size 10
    pool-timeout 30.0
    cache-local-mb 16
    blob-temp-dir /var/zodb/tmp
    s3-bucket-name my-bucket
    s3-endpoint-url https://s3.amazonaws.com
    s3-region us-east-1
    blob-threshold 100KB
    blob-cache-dir /var/zodb/blobcache
    blob-cache-size 1GB
  </pgjsonb>
  mount-point /
  cache-size 30000
</zodb_db>
```

| Key | Default | Description |
|---|---|---|
| dsn | *required* | PostgreSQL connection string (libpq or URI) |
| name | pgjsonb | Storage name |
| history-preserving | false | Enable history-preserving mode |
| cache-local-mb | 16 | Per-instance LRU cache (MB) |
| pool-size | 1 | Min pool connections |
| pool-max-size | 10 | Max pool connections |
| pool-timeout | 30.0 | Connection acquisition timeout (seconds) |
| blob-temp-dir | auto | Temporary blob directory |
| blob-threshold | 100KB | S3 tiering threshold |
| s3-bucket-name | none | S3 bucket (enables tiering) |
| s3-endpoint-url | none | S3 endpoint (MinIO, Ceph) |
| s3-region | none | AWS region |
| s3-access-key | none | AWS access key |
| s3-secret-key | none | AWS secret key |
| s3-use-ssl | true | Enable SSL for S3 |
| s3-prefix | "" | S3 key prefix |
| blob-cache-dir | none | Local cache for S3 blobs |
| blob-cache-size | 1GB | Max local cache size |

## Python API

```python
from zodb_pgjsonb import PGJsonbStorage
import ZODB

storage = PGJsonbStorage(dsn="dbname=zodb user=zodb host=localhost")
db = ZODB.DB(storage)
conn = db.open()
root = conn.root()
root["hello"] = "world"
import transaction
transaction.commit()
```

### SQL Queryability

```sql
-- List all object types
SELECT class_mod || '.' || class_name AS class, count(*)
FROM object_state GROUP BY 1 ORDER BY 2 DESC;

-- Find Plone content
SELECT zoid, state->>'title' AS title
FROM object_state
WHERE class_mod LIKE 'plone.app.contenttypes%';

-- Query by JSONB key
SELECT zoid, state->>'title'
FROM object_state
WHERE state @> '{"portal_type": "Document"}';
```

### Migration (zodbconvert)

```python
storage = PGJsonbStorage(dsn="...")
storage.copyTransactionsFrom(source_storage, workers=4)  # parallel blob-aware copy
storage.copyTransactionsFrom(source, workers=4, start_tid=tid)  # incremental resume
```

### Blob Statistics

```python
stats = storage.get_blob_stats()
# {'total_blobs': 1234, 'total_size': 567890, 'pg_size': 123456, 's3_size': 444434, ...}

histogram = storage.get_blob_histogram()
# [{'label': '0-1KB', 'count': 100, 'pct': 8.1, 'tier': 'pg'}, ...]
```

## Performance vs RelStorage

| Category | vs RelStorage |
|---|---|
| Single store | 1.4-1.6x faster |
| Cached load | 3.7-4.4x faster |
| Uncached load | 1.1-1.6x slower (transcode overhead) |
| Pack/GC (10K objects) | 22x faster |
| Batch store 100 | 1.2x slower (JSONB indexing) |
| HP undo | 1.8x faster |

## Security

- JSON storage eliminates pickle deserialization attack surface
- `_RestrictedUnpickler` for legacy pickle extension data (blocks arbitrary code execution)
- `ExtraColumn.name` validated against SQL identifier pattern (injection prevention)
- DSN credentials masked in debug logs
- Blob files restricted to 0o600 (owner-only)
- Connection pool timeout prevents unbounded waits (DoS mitigation)

## Ecosystem

- **zodb-json-codec**: Rust pickle↔JSON codec (dependency, installed automatically)
- **plone-pgcatalog**: PostgreSQL-backed catalog using state processor plugin
- **plone-pgthumbor**: Thumbor image scaling reading from blob_state table
- **zodb-s3blobs**: S3 blob backend (optional dependency for tiered storage)

## Documentation Sections

- [Tutorials](tutorials/index.md): Step-by-step lessons (quickstart Docker, migration)
- [How-To Guides](how-to/index.md): Task-focused solutions (install, S3, history modes, SQL queries, deployment)
- [Reference](reference/index.md): Configuration, schema, storage API, state processor API, changelog
- [Explanation](explanation/index.md): Architecture, why JSONB, performance, security
