1.4 KiB
Event log based store
The data rows of our table are to be recreated from an event log All interactions with the rows is to happen exclusively via events from/in the log For performance reasons we are to cache these data rows as well for quick lookup
Events in the log are to take form of: type Event struct { Seq int Type "create"|"update"|"delete" Hash string ItemID string // uuid-v4 EventID string // uuid-v4 Data map[string]interface{} Timestamp datetime } Events are divided into 3 types, create update and delete events Create events simply create the object as given in Data Delete events simply mark an object as deleted (not actually delete!) via its ItemID Update events are to modify a field of a row and never more than one field Therefore its data is only the diff in the form of "age = 3"
When creating an event only the Type and ItemID must be provided Data is optional (delete events have no data) Hash, EventID and Seq are to be computed server side
On the server side with an incoming event: Grab the latest event Assign the event a sequence number that is incremented from the latest Create its EventID (generate a uuid-v4) Assign it a Timestamp Compute the hash from the dump of the current event PLUS the previous event's hash And only then apply the patch For create events that is insert objects For delete events that is mark objects as deleted For update events get the object, apply the diff and sav the object