MinerSectorInfo returns nil, nil if sector is not found.

EnvDisablePreMigrations when set to '1' stops pre-migrations from running.

PreMigration describes a pre-migration step to prepare for a network state upgrade.

MigrationCache can be used to cache information used by a migration.

MigrationFunc is a migration function run at every upgrade.

PreMigrationFunc is a function run _before_ a network upgrade to pre-compute part of the network upgrade and speed it up.