3.1 Schema Version

2 min read

Every hive database carries a schema version in a single-row table :

CREATE TABLE schema_version (
    version INTEGER NOT NULL
);

The current version is 1 — the only version that has existed.

loregd checks the version as it opens each database (§2.2, step 4) and takes one of three paths:

StateBehaviour
No schema_version tableThe database is new. loregd creates the persistent tables, the volatile tables, and inserts version 1, all in one transaction.
Version equals 1Normal startup.
Version greater than 1Startup fails. The database was written by a newer loregd, and proceeding risks corrupting it by writing through an older understanding of its layout.
Version less than 1Startup fails.

There are no migrations. loregd carries no migration table, no migration step list, and no upgrade path; an older database is reported as requiring migration and startup stops there. Since 1 is the only version ever assigned, this does not arise in practice — but a second version cannot be stamped without building the migration machinery first.

Two details of the check are worth knowing. The schema_version table has no primary key, uniqueness constraint, or check constraint, so a second row is not detected: the first row read wins.

And because every table is created with IF NOT EXISTS, a database holding the data tables but no schema_version table is stamped as version 1 without any validation that its contents match that layout.

Edit this page