cosmos-sdk/store

Store

CacheKV

cachekv.Store is a wrapper KVStore which provides buffered writing / cached reading functionalities over the underlying KVStore.

type Store struct {
    cache map[string]cValue
    parent types.KVStore
}

Get

Store.Get() checks Store.cache first in order to find if there is any cached value associated with the key. If the value exists, the function returns it. If not, the function calls Store.parent.Get(), sets the key-value pair to the Store.cache, and returns it.

Set

Store.Set() sets the key-value pair to the Store.cache. cValue has the field dirty bool which indicates whether the cached value is different from the underlying value. When Store.Set() cache new pair, the cValue.dirty is set true so when Store.Write() is called it can be written to the underlying store.

Iterator

Store.Iterator() have to traverse on both caches items and the original items. In Store.iterator(), two iterators are generated for each of them, and merged. memIterator is essentially a slice of the KVPairs, used for cached items. mergeIterator is a combination of two iterators, where traverse happens ordered on both iterators.

CacheMulti

cachemulti.Store is a wrapper MultiStore which provides buffered writing / cached reading functionalities over the underlying MutliStore

type Store struct {
    db types.CacheKVStore
    stores map[types.StoreKey] types.CacheWrap
}

cachemulti.Store branches all substores in its constructor and hold them in Store.stores. Store.GetKVStore() returns the store from Store.stores, and Store.Write() recursively calls CacheWrap.Write() on the substores.

DBAdapter

dbadapter.Store is a adapter for dbm.DB making it fulfilling the KVStore interface.

type Store struct {
    dbm.DB
}

dbadapter.Store embeds dbm.DB, so most of the KVStore interface functions are implemented. The other functions(mostly miscellaneous) are manually implemented.

IAVL

iavl.Store is a base-layer self-balancing merkle tree. It is guaranteed that

1. Get & set operations are O(log n), where n is the number of elements in the tree
2. Iteration efficiently returns the sorted elements within the range
3. Each tree version is immutable and can be retrieved even after a commit(depending on the pruning settings)

Specification and implementation of IAVL tree can be found in [https://github.com/tendermint/iavl].

GasKV

gaskv.Store is a wrapper KVStore which provides gas consuming functionalities over the underlying KVStore.

type Store struct {
    gasMeter types.GasMeter
    gasConfig types.GasConfig
    parent types.KVStore
}

When each KVStore methods are called, gaskv.Store automatically consumes appropriate amount of gas depending on the Store.gasConfig.

Prefix

prefix.Store is a wrapper KVStore which provides automatic key-prefixing functionalities over the underlying KVStore.

type Store struct {
    parent types.KVStore
    prefix []byte
}

When Store.{Get, Set}() is called, the store forwards the call to its parent, with the key prefixed with the Store.prefix.

When Store.Iterator() is called, it does not simply prefix the Store.prefix, since it does not work as intended. In that case, some of the elements are traversed even they are not starting with the prefix.

RootMulti

rootmulti.Store is a base-layer MultiStore where multiple KVStore can be mounted on it and retrieved via object-capability keys. The keys are memory addresses, so it is impossible to forge the key unless an object is a valid owner(or a receiver) of the key, according to the object capability principles.

TraceKV

tracekv.Store is a wrapper KVStore which provides operation tracing functionalities over the underlying KVStore.

type Store struct {
    parent types.KVStore
    writer io.Writer
    context types.TraceContext
}

When each KVStore methods are called, tracekv.Store automatically logs traceOperation to the Store.writer.

type traceOperation struct {
    Operation operation
    Key string
    Value string
    Metadata map[string]interface{}
} 

traceOperation.Metadata is filled with Store.context when it is not nil. TraceContext is a map[string]interface{}.

Transient

transient.Store is a base-layer KVStore which is automatically discarded at the end of the block.

type Store struct {
    dbadapter.Store
}

Store.Store is a dbadapter.Store with a dbm.NewMemDB(). All KVStore methods are reused. When Store.Commit() is called, new dbadapter.Store is assigned, discarding previous reference and making it garbage collected.