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It is common for many accounts to share the same code - at the database level, code is stored by hash meaning only one copy exists per unique program but when loaded in memory, a copy is made for each account. Further, every time we execute the code, it must be scanned for invalid jump destinations which slows down EVM exeuction. Finally, the extcodesize call causes code to be loaded even if only the size is needed. This PR improves on all these points by introducing a shared CodeBytesRef type whose code section is immutable and that can be shared between accounts. Further, a dedicated `len` API call is added so that the EXTCODESIZE opcode can operate without polluting the GC and code cache, for cases where only the size is requested - rocksdb will in this case cache the code itself in the row cache meaning that lookup of the code itself remains fast when length is asked for first. With 16k code entries, there's a 90% hit rate which goes up to 99% during the 2.3M attack - the cache significantly lowers memory consumption and execution time not only during this event but across the board.
Core database replacement wrapper object
This wrapper replaces the TrieDatabaseRef and its derivatives by the new object CoreDbRef.
Relations to current TrieDatabaseRef implementation
Here are some incomplete translations for objects and constructors.
Object types:
| Legacy notation | CoreDbRef based replacement |
|---|---|
| ChainDB | (don't use/avoid) |
| ChainDbRef | CoreDbRef |
| TrieDatabaseRef | CoreDbKvtRef |
| HexaryTrie | CoreDbMptRef |
| SecureHexaryTrie | CoreDbPhkRef |
| DbTransaction | CoreDbTxRef |
| TransactionID | CoreDbTxID |
Constructors:
| Legacy notation | CoreDbRef based replacement |
|---|---|
| trieDB newChainDB("..") | newCoreDbRef(LegacyDbPersistent,"..") |
| newMemoryDB() | newCoreDbRef(LegacyDbMemory) |
| -- | |
| initHexaryTrie(db,..) | db.mpt(..) (no pruning) |
| db.mptPrune(..) (w/pruning true/false) | |
| -- | |
| initSecureHexaryTrie(db,..) | db.phk(..) (no pruning) |
| db.phkPrune(..) (w/pruning true/false) | |
| -- | |
| newCaptureDB(db,memDB) | db.capture() (see below) |
Usage of the replacement wrapper
Objects pedigree:
CoreDbRef -- base descriptor
| | |
| | +--- CoreDbCtxRef -- MPT context descriptor
| | | |
| | | +-- CoreDbMptRef -- hexary trie instance
| | | | : :
| | | +-- CoreDbMptRef -- hexary trie instance
| | |
| | |
| | +---- CoreDbPhkRef -- pre-hashed key hexary trie instance
| | | : :
| | +---- CoreDbPhkRef -- pre-hashed key hexary trie instance
| |
| |
| +------ CoreDbKvtRef -- single static key-value table
|
|
+-------- CoreDbCaptRef -- tracer support descriptor
Instantiating legacy standard database object descriptors works as follows:
let
db = newCoreDbRef(..) # new base descriptor
mpt = db.mpt(..) # hexary trie/Merkle Patricia Tree
phk = db.phk(..) # pre-hashed key hexary trie/MPT
kvt = db.kvt # key-value table
Tracer support setup by hiding the current CoreDbRef behind a replacement:
let
capture = db.capture()
db = capture.recorder # use the recorder in place of db
...
for key,value in capture.recorder.kvt:
... # process recorded data