Database schemas and migrations

RustBox 0.2.14 keeps SQL, blob storage and search as independent concerns:

database_backend = sqlite | mysql | pgsql
session_backend  = database | redis
storage.backend  = filesystem | s3
search.backend   = disabled | local_tantivy | opensearch

When session_backend = "database", sessions live in the selected SQL database. session_backend = "redis" moves only session persistence to Redis/Redis Sentinel.

Layout

migrations/
├── sqlite/
│   ├── schema.sql
│   ├── V047__blob_keys_and_search_outbox.sql
│   ├── V048__folder_counter_generation.sql
│   ├── V049__blob_delete_outbox.sql
│   └── V050__compact_rows_and_signature_mode.sql
├── mysql/
│   ├── schema.sql
│   ├── V047__blob_keys_and_search_outbox.sql
│   ├── V048__folder_counter_generation.sql
│   ├── V049__blob_delete_outbox.sql
│   └── V050__compact_rows_and_signature_mode.sql
└── pgsql/
    ├── schema.sql
    ├── V047__blob_keys_and_search_outbox.sql
    ├── V048__folder_counter_generation.sql
    ├── V049__blob_delete_outbox.sql
    └── V050__compact_rows_and_signature_mode.sql

Each schema.sql is the current complete schema for fresh installations. The historical compatibility baseline remains V046. RustBox 0.2.1 adds V047, which adds attachment SHA-256 metadata and the durable search outbox used by external indexing. RustBox 0.2.8 adds V048, which adds the monotonic folders.counter_generation used to reject stale IMAP counter writes even when the numeric counts temporarily return to an earlier value. RustBox 0.2.13 adds V049, the durable blob_delete_outbox used to retry physical object deletion after metadata is removed. RustBox 0.2.14 adds V050, which stores the default-on compact wide-row preference and each identity's signature insertion mode (silent or visible).

Account data is isolated inside the selected physical database with a deterministic, collision-checked table prefix derived from the account hash. The {{p}} marker in tenant SQL is replaced by RustBox at provisioning/migration time. Sessions are global and therefore are not prefixed.

Runtime migrations

Every schema-changing release must add the same logical migration for all supported SQL engines and register it in src/db/pool.rs. Do not update only schema.sql: fresh installs use the baseline while existing installations use the numbered migration path.

RustBox 0.2.14 adds runtime migration V050 on SQLite, MySQL and PostgreSQL. V051 is the next migration number.

Redis and Redis Sentinel do not use SQL migrations.

Engine notes

SQLite uses data_dir/rustbox.sqlite by default; database_url may point to another persistent SQLite file.
MySQL requires database_url and targets MySQL 8.0.13 or newer.
PostgreSQL requires database_url.
MySQL/PostgreSQL are full application backends, not session-only databases.
The SQL engine does not choose blob/search storage. PostgreSQL/MySQL may still use local filesystem/Tantivy in single-node mode.
Cluster mode requires a shared MySQL/PostgreSQL database plus cluster-safe blob/search choices; local data_dir is not inherently required.