Crate massa_event_cache
source ·Expand description
§General description
A database (build on top of rocksdb) to store final events emitted by:
- The massa node during execution
- A Smart contract during execution
The database can also be queried with: get_filtered_sc_output_events
§Architecture
- controller.rs / worker.rs: db wrapper controller & worker
- rocksdb_operator: a rocksdb operator to handle counter (as u64 counter)
- ser_deser.rs: event serializer && deserializer (using nom)
- event_cache: db over rocksdb code
§DBKeyBuilder
The db use the DbKeyBuilder structure to create the rocksdb keys required for its operations. There are 3 types of keys:
- regular key: and the associated value is the event data serialized
- prefix key: Key used to iterate in rocksdb
- counter key: key used to query count info (example: number of event for operation id X)
See key_from_event method for more information about the keys.
§Db queries
WHen inserting an event in the DB, counters are being updated. They are used later when we need to query the DB in order to query by ordering with counter values (to optimize the DB query plan).
Let say you want to query events for a specific slot range && an emitter_address, the query method will first query the counts for each filter item then select the one with fewer rows then select the other.
§Snip
The method snip on the DB must be used to remove items and keep a reasonable DB size. It will remove the oldest (by slot) items (number is configurable) in the DB.
§Tests
- Check unit tests for info on how to use the DB directly.