update.go

package wal

// Update defines a single update that can be sent to the WAL and saved
// atomically. Updates are sent to the wal in groups of one or more, and upon
// being signaled, will be saved to disk in a high-integrity, all- or-nothing
// fasion that follows ACID principles.
//
// The name and version are optional, however best-practice code will make use
// of these fields.
//
// When using the Update, it recommended that you typecast the Update type to
// another type which has methods on it for creating and applying the Update +
// instructions, including any special handling based on the version.
type Update struct {
	// The name of the update type. When the WAL is loaded after an unclean
	// shutdown, any un-committed changes will be passed as Updates back to the
	// caller instantiating the WAL. The caller should determine what code to
	// run on the the update based on the name and version.
	Name string

	// The version of the update type. Update types and implementations can be
	// tweaked over time, and a version field allows for easy compatibility
	// between releases, even if an upgrade occurs between an unclean shutdown
	// and a reload.
	Version string

	// The marshalled data directing the update. The data is an opaque set of
	// instructions to follow that implement and idempotent change to a set of
	// persistent files. A series of unclean shutdowns in rapid succession could
	// mean that these instructions get followed multiple times, which means
	// idempotent instructions are required.
	Instructions []byte
}