3320c24afa
Add CRC32C checksums to WAL record format (v2), implement crash recovery with automatic truncation of corrupt records, add feature-gated group commit buffer for batched fsync under concurrent load, and implement log rotation via segment files with global offset addressing. Key changes: - Record format v2: [len:u32][crc32c:u32][blake3:32][payload:N] - recover_file() scans and truncates corrupt tail records - GroupCommitBuffer batches fsync via MPSC channel (tokio feature gate) - SegmentManager with binary search resolution and cursor-based cleanup - Journal::read() auto-refreshes segments on miss for writer/reader split - Split recovery.rs and key_codec.rs into directory modules for 500-line max Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
98 lines
3.2 KiB
Markdown
98 lines
3.2 KiB
Markdown
# Storage
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**Last Updated:** 2026-01-31
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**Confidence:** High
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## Summary
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Episteme uses a Log-Structured, Content-Addressed storage model. Writes append to WAL, then index asynchronously. Reads query indexes and apply Lenses.
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**Key Facts:**
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- Append-only (never mutate)
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- WAL for durability (fsync on write)
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- KV store: HybridStore (fjall for writes, redb for reads)
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- Content-addressed by BLAKE3 hash
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**File Pointers:**
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- `crates/stemedb-storage/src/traits.rs` - KVStore trait
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- `crates/stemedb-storage/src/hybrid_backend.rs` - HybridStore (routes to fjall or redb)
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- `crates/stemedb-storage/src/fjall_backend.rs` - FjallStore (write-heavy keys)
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- `crates/stemedb-storage/src/redb_backend.rs` - RedbStore (read-heavy keys)
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- `crates/stemedb-storage/src/serde_helpers.rs` - Storage-layer serialize/deserialize helpers
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- `crates/stemedb-storage/src/vote_store.rs` - VoteStore (Ballot Box)
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- `crates/stemedb-storage/src/index_store.rs` - IndexStore (S: and SP: indexes)
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- `crates/stemedb-storage/src/trust_rank_store.rs` - TrustRankStore (TR:)
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## KV Layout
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| Key Pattern | Value | Purpose |
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|-------------|-------|---------|
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| `H:{Hash}` | `Assertion` (serialized) | Main content store |
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| `V:{assertion_hash}:{vote_hash}` | `Vote` (serialized) | Ballot Box votes |
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| `VC:{assertion_hash}` | `u64` (LE bytes) | Vote count cache |
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| `VW:{assertion_hash}` | `f32` (LE bytes) | Aggregate weight cache |
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| `E:{epoch_id}` | `Epoch` (serialized) | Paradigm definitions |
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| `S:{Subject}` | `Vec<Hash>` (rkyv) | Subject index (IndexStore) |
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| `SP:{Subject}:{Predicate}` | `Vec<Hash>` (rkyv) | Compound index (IndexStore) |
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| `TR:{AgentId}` | `TrustRank` (rkyv) | Agent reputation (TrustRankStore) |
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| `MV:{Subject}:{Predicate}` | `MaterializedView` (rkyv) | Pre-computed winner (Materializer) |
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| `__CURSOR__:ingest` | `u64` (LE bytes) | Ingestion WAL offset checkpoint |
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## Serialization
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### stemedb-core (shared types)
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For core types, use the canonical module:
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```rust
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use stemedb_core::serde::{serialize, deserialize};
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let bytes = serialize(&my_value)?;
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let value: MyType = deserialize(&bytes)?;
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```
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**File:** `crates/stemedb-core/src/serde.rs`
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Raw `AllocSerializer` usage is prohibited in production code (enforced via CLAUDE.md).
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### stemedb-storage (store implementations)
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In storage modules, use the storage-layer helpers that map to `StorageError`:
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```rust
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use crate::serde_helpers::{serialize, deserialize};
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let bytes = serialize(&my_value)?; // Returns Result<Vec<u8>, StorageError>
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let value: MyType = deserialize(&bytes)?;
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```
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**File:** `crates/stemedb-storage/src/serde_helpers.rs`
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This provides unified error handling across all store implementations (VoteStore, IndexStore, TrustRankStore, AuditStore, TrustPackStore, QuotaStore).
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## Write Path
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```
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1. Agent submits signed Assertion
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2. Validate signature
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3. Append to WAL (fsync)
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4. Return 202 Accepted with Hash
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5. Background: tail WAL -> update indexes
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```
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## Read Path
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```
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1. Query: GET(Subject, Predicate, Lens)
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2. Lookup: SP:{Subject}:{Predicate} -> [Hash...]
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3. Hydrate: Load assertions from H:{Hash}
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4. Resolve: Apply Lens
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5. Return: Deterministic answer
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```
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## Related Topics
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- [Assertion](./assertion.md)
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- [Ballot Box](./ballot-box.md) - High-velocity vote storage
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- [Architecture](../../../architecture.md)
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