hike allocations (and the garbage collection maintenance that follows)
are responsible for some 10% of cpu time (not wall time!) at this point
- this PR avoids them by stepping through the layers one step at a time,
simplifying the code at the same time.
The state and account MPT:s currenty share key space in the database
based on that vertex id:s are assigned essentially randomly, which means
that when two adjacent slot values from the same contract are accessed,
they might reside at large distance from each other.
Here, we prefix each vertex id by its root causing them to be sorted
together thus bringing all data belonging to a particular contract
closer together - the same effect also happens for the main state MPT
whose nodes now end up clustered together more tightly.
In the future, the prefix given to the storage keys can also be used to
perform range operations such as reading all the storage at once and/or
deleting an account with a batch operation.
Notably, parts of the API already supported this rooting concept while
parts didn't - this PR makes the API consistent by always working with a
root+vid.
* Update some docu
* Resolve obsolete compile time option
why:
Not optional anymore
* Update checks
why:
The notion of what constitutes a valid `Aristo` db has changed due to
(even more) lazy calculating Merkle hash keys.
* Disable redundant unit test for production
* Remove `dirty` set from structural objects
why:
Not used anymore, the tree is dirty by default.
* Rename `aristo_hashify` -> `aristo_compute`
* Remove cruft, update comments, cosmetics, etc.
* Simplify `SavedState` object
why:
The key chaining have become obsolete after extra lazy hashing. There
is some available space for a state hash to be maintained in future.
details:
Accept the legacy `SavedState` object serialisation format for a
while (which will be overwritten by new format.)
* Tighten `CoreDb` API for accounts
why:
Apart from cruft, the way to fetch the accounts state root via a
`CoreDbColRef` record was unnecessarily complicated.
* Extend `CoreDb` API for accounts to cover storage tries
why:
In future, this will make the notion of column objects obsolete. Storage
trees will then be indexed by the account address rather than the vertex
ID equivalent like a `CoreDbColRef`.
* Apply new/extended accounts API to ledger and tests
details:
This makes the `distinct_ledger` module obsolete
* Remove column object constructors
why:
They were needed as an abstraction of MPT sub-trees including storage
trees. Now, storage trees are handled by the account (e.g. via address)
they belong to and all other trees can be identified by a constant well
known vertex ID. So there is no need for column objects anymore.
Still there are some left-over column object methods wnich will be
removed next.
* Remove `serialise()` and `PayloadRef` from default Aristo API
why:
Not needed. `PayloadRef` was used for unstructured/unknown payload
formats (account or blob) and `serialise()` was used for decodng
`PayloadRef`. Now it is known in advance what the payload looks
like.
* Added query function `hasStorageData()` whether a storage area exists
why:
Useful for supporting `slotStateEmpty()` of the `CoreDb` API
* In the `Ledger` replace `storage.stateEmpty()` by `slotStateEmpty()`
* On Aristo, hide the storage root/vertex ID in the `PayloadRef`
why:
The storage vertex ID is fully controlled by Aristo while the
`AristoAccount` object is controlled by the application. With the
storage root part of the `AristoAccount` object, there was a useless
administrative burden to keep that storage root field up to date.
* Remove cruft, update comments etc.
* Update changed MPT access paradigms
why:
Fixes verified proxy tests
* Fluffy cosmetics
This buffer eleminates a large part of allocations during MPT traversal,
reducing overall memory usage and GC pressure.
Ideally, we would use it throughout in the API instead of
`openArray[byte]` since the built-in length limit appropriately exposes
the natural 64-nibble depth constraint that `openArray` fails to
capture.
* Use RocksDb column families instead of a prefixed single column
why:
Better performance
* Use structural objects `VertexRef` and `HashKey` in LRU cache for RocksDb
why:
Avoids repeated de/serialisation
* Remove all journal related stuff
* Refactor function names journal*() => delta*(), filter*() => delta*()
* remove `trg` fileld from `FilterRef`
why:
Same as `kMap[$1]`
* Re-type FilterRef.src as `HashKey`
why:
So it is directly comparable to `kMap[$1]`
* Moved `vGen[]` field from `LayerFinalRef` to `LayerDeltaRef`
why:
Then a separate `FilterRef` type is not needed, anymore
* Rename `roFilter` field in `AristoDbRef` => `balancer`
why:
New name more appropriate.
* Replace `FilterRef` by `LayerDeltaRef` type
why:
This allows to avoid copying into the `balancer` (see next patch set)
most of the time. Typically, only one instance is running on the backend
and the `balancer` is only used as a stage before saving data.
* Refactor way how to store data persistently
why:
Avoid useless copy when staging `top` layer for persistently saving to
backend.
* Fix copyright header?
* Update TDD suite logger output format choices
why:
New format is not practical for TDD as it just dumps data across a wide
range (considerably larder than 80 columns.)
So the new format can be turned on by function argument.
* Update unit tests samples configuration
why:
Slightly changed the way to find the `era1` directory
* Remove compiler warnings (fix deprecated expressions and phrases)
* Update `Aristo` debugging tools
* Always update the `storageID` field of account leaf vertices
why:
Storage tries are weekly linked to an account leaf object in that
the `storageID` field is updated by the application.
Previously, `Aristo` verified that leaf objects make sense when passed
to the database. As a consequence
* the database was inconsistent for a short while
* the burden for correctness was all on the application which led
to delayed error handling which is hard to debug.
So `Aristo` will internally update the account leaf objects so that
there are no race conditions due to the storage trie handling
* Aristo: Let `stow()`/`persist()` bail out unless there is a `VertexID(1)`
why:
The journal and filter logic depends on the hash of the `VertexID(1)`
which is commonly known as the state root. This implies that all
changes to the database are somehow related to that.
* Make sure that a `Ledger` account does not overwrite the storage trie reference
why:
Due to the abstraction of a sub-trie (now referred to as column with a
hash describing its state) there was a weakness in the `Aristo` handler
where an account leaf could be overwritten though changing the validity
of the database. This has been changed and the database will now reject
such changes.
This patch fixes the behaviour on the application layer. In particular,
the column handle returned by the `CoreDb` needs to be updated by
the `Aristo` database state. This mitigates the problem that a storage
trie might have vanished or re-apperaed with a different vertex ID.
* Fix sub-trie deletion test
why:
Was originally hinged on `VertexID(1)` which cannot be wholesale
deleted anymore after the last Aristo update. Also, running with
`VertexID(2)` needs an artificial `VertexID(1)` for making `stow()`
or `persist()` work.
* Cosmetics
* Activate `test_generalstate_json`
* Temporarily `deactivate test_tracer_json`
* Fix copyright header
---------
Co-authored-by: jordan <jordan@dry.pudding>
Co-authored-by: Jacek Sieka <jacek@status.im>
* Aristo: Rename journal related sources and functions
why:
Previously, the naming was hinged on the phrases `fifo`, `filter` etc.
which reflect the inner workings of cascaded filters. This was
unfortunate for reading/understanding the source code for actions where
the focus is the journal as a whole.
* Aristo: Fix buffer overflow (path length truncating error)
* Aristo: Tighten `hikeUp()` stop check, update error code
why:
Detect dangling vertex links. These are legit with `snap` sync
processing but not with regular processing.
* Aristo: Raise assert in regular mode `merge()` at a dangling link/edge
why:
With `snap` sync processing, partial trees are ok and can be amended.
Not so in regular mode.
Previously there was only a debug message when a non-legit dangling edge
was encountered.
* Aristo: Make sure that vertices are copied before modification
why:
Otherwise vertices from lower layers might also be modified
* Aristo: Fix relaxed mode for validity checker `check()`
* Remove cruft
* Aristo: Update API for transaction handling
details:
+ Split `aristo_tx.nim` into sub-modules
+ Split `forkWith()` into `findTx()` + `forkTx()`
+ Removed `forkTop()`, `forkBase()` (now superseded by new `forkTx()`)
* CoreDb+Aristo: Fix initialiser (missing methods)
* Aristo: Code cosmetics, e.g. update some CamelCase names
* CoreDb+Aristo: Provide oldest known state root implied
details:
The Aristo journal allows to recover earlier but not all state roots.
* Aristo: Fix journal backward index operator, e.g. `[^1]`
* Aristo: Fix journal updater
why:
The `fifosStore()` store function slightly misinterpreted the update
instructions when translation is to database `put()` functions. The
effect was that the journal was ever growing due to stale entries which
were never deleted.
* CoreDb+Aristo: Provide utils for purging stale data from the KVT
details:
See earlier patch, not all state roots are available. This patch
provides a mapping from some state root to a block number and allows to
remove all KVT data related to a particular block number
* Aristo+Kvt: Implement a clean up schedule for expired data in KVT
why:
For a single state ledger like `Aristo`, there is only a limited
backlog of states. So KVT data (i.e. headers etc.) are cleaned up
regularly
* Fix copyright year
* Code cosmetics
* Aristo+Kvt: Fix api wrappers
why:
Api setup killed the backend descriptor when backend mapping was
disabled.
* Aristo: Implement masked profiling entries
why:
Database backend should be listed but not counted in tally
* CoreDb: Simplify backend() methods
why:
DBMS backend access Was provided very early and over engineered. Now
there are only two backend machines, one for `Kvt` and the other one
for an `Mpt` available only via new API.
* CoreDb: Code cleanup regarding descriptor types
* CoreDb: Refactor/redefine `persistent()` methods
why:
There were `persistent()` methods for any type of caching storage
facilities `Kvt`, `Mpt`, `Phk`, and `Acc`. Now there is only a single
`persistent()` method storing all facilities in tandem (similar to
how transactions work.)
For non shared `Kvt` tables, there is now an extra storage method
`saveOffSite()`.
* CoreDb lingo update: `trie` becomes `column`
why:
Notion of a `trie` is pretty much hidden by the new `CoreDb` api.
Revealed are sort of database columns for accounts an storage data,
any of which have an internal state represented by a Keccack hash.
So a `trie` or `MPT` becomes a `column` and a `rootHash` becomes a
column state.
* Aristo: rename backend filed `filters` => `journal`
* Update full sync logging
details:
+ Disable eth handler noise while syncing
+ Log journal depth (if available)
* Fix copyright year
* Fix cruft and unwanted imports
* Aristo/Kvt: Provide function hooks APIs
why:
These APIs can be used for installing tracers, profiling functoinality,
and other niceties on the databases.
* Aristo: Provide optional API profiling
details:
It basically is a re-implementation of the `CoreDb` profiling
implementation
* Kvt: Provide optional API profiling similar to `Aristo`
* CoreDb: Re-implementing profiling using `aristo_profile`
* Ledger: Re-implementing profiling using `aristo_profile`
* CoreDb: Update unit tests for maintainability
* update copyright dates
* Aristo: Reorg `hashify()` using different schedule algorithm
why:
Directly calculating the search tree top down from the roots turns
out to be faster than using the cached structures left over by `merge()`
and `delete()`.
Time gains is short of 20%
* Aristo: Remove `lTab[]` leaf entry object type
why:
Not used anymore. It was previously needed to build the schedule for
`hashify()`.
* Aristo: Avoid unnecessary re-org of the vertex ID recycling list
why:
This list can become quite large so a heuristic is employed whether
it makes sense to re-org.
Also, re-org check is only done by `delete()` functions.
* Aristo: Remove key/reverse lookup table from tx layers
why:
It is ignored except for handling proof nodes and costs unnecessary
run time resources.
This feature was originally needed to accommodate the mental transition
from the legacy MPT to the `Aristo` trie :).
* Fix copyright year
* CoreDb: update test suite
* Aristo: Simplify reverse key map
why:
The reverse key map `pAmk: (root,key) -> {vid,..}` as been simplified to
`pAmk: key -> {vid,..}` as the state `root` domain argument is not used,
anymore
* Aristo: Remove `HashLabel` object type and replace it by `HashKey`
why:
The `HashLabel` object attaches a root hash to a hash key. This is
nowhere used, anymore.
* Fix copyright
* Aristo: Update unit test suite
* Aristo/Kvt: Fix iterators
why:
Generic iterators were not properly updated after backend change
* Aristo: Add sub-trie deletion functionality
why:
For storage tries linked to an account payload vertex ID, a the
whole storage trie needs to be deleted with the account.
* Aristo: Reserve vertex ID numbers for static custom state roots
why:
Static custom state roots may be controlled by an application,
e.g. for a receipt or a transaction root. The `Aristo` functions
are agnostic of what the static state roots are when different
from the internal tree vertex ID 1.
details;
The `merge()` function applied to a non-static state root (assumed
to be a storage root) will check the payload of an accounts leaf
and mark its Merkle keys to be re-checked.
* Aristo: Correct error code symbol
* Aristo: Update error code symbols
* Aristo: Code cosmetics/comments
* Aristo: Fix hashify schedule calculator
why:
Had a tendency to stop early leaving an incomplete job
* Update KVT layers abstraction
details:
modelled after Aristo layers
* Simplified KVT database iterators (removed item counters)
why:
Not needed for production functions
* Simplify KVT merge function `layersCc()`
* Simplified Aristo database iterators (removed item counters)
why:
Not needed for production functions
* Update failure condition for hash labels compiler `hashify()`
why:
Node need not be rejected as long as links are on the schedule. In
that case, `redo[]` is to become `wff.base[]` at a later stage.
* Update merging layers and label update functions
why:
+ Merging a stack of layers with `layersCc()` could be simplified
+ Merging layers will optimise the reverse `kMap[]` table maps
`pAmk: label->{vid, ..}` by deleting empty mappings `label->{}` where
they are redundant.
+ Updated `layersPutLabel()` for optimising `pAmk[]` tables
* Fix kvt headers
* Provide differential layers for KVT transaction stack
why:
Significant performance improvement
* Provide abstraction layer for database top cache layer
why:
This will eventually implemented as a differential database layers
or transaction layers. The latter is needed to improve performance.
behavioural changes:
Zero vertex and keys (i.e. delete requests) are not optimised out
until the last layer is written to the database.
* Provide differential layers for Aristo transaction stack
why:
Significant performance improvement
* Explicitly use shared `Kvt` table on `Ledger` and `Clique` lookup.
why:
Speeds up lookup time with `Aristo` backend. For writing `Clique` data,
the `Companion` model allows to write `Clique` data past the database
locked by evm transactions.
* Implement `CoreDb` profiling with API tracking
why:
Chasing time spent per APT procs ...
* Implement `Ledger` profiling with API tracking
why:
Chasing time spent per APT procs ...
* Always hashify when commiting or storing
why:
A dirty cache makes no sense when committing
* Make sure that a zero key is created when adding/updating vertices
why:
This is an error fix mainly for edge cases. A typical error was
that the root key got deleted when there were only a few vertices
left on the DB.
* Need all created and changed vertices zero-keyed on the cache
why:
A zero key (i.e. empty Merkle hash) indicates that a vertex key
needs to be updated. This would not be needed immediately after
a merge as there is an actual leaf path on the cache layer. But
after subsequent merge and delete operations this information
might get blurred.
* Re-org hashing algorithm
why:
Apart from errors, the previous implementation was too slow for
two reasons:
+ some control hashes were calculated for debugging (now all
verification is done in `aristo_check` module)
+ the leaf paths stored on the cache are used to build the
labelling (aka hashing) schedule; there paths were accumulated
over successive hash sessions although it is clear that all
keys were generated, already
* Register paths for added leafs because of trie re-balancing
why:
While the payload would not change, the prefix in the leaf vertex
would. So it needs to be flagged for hash recompilation for the
`hashify()` module.
also:
Make sure that `Hike` paths which might have vertex links into the
backend filter are replaced by vertex copies before manipulating.
Otherwise the vertices on the immutable filter might be involuntarily
changed.
* Also check for paths where the leaf vertex is on the backend, already
why:
A a path can have dome vertices on the top layer cache with the
`Leaf` vertex on the backend.
* Re-define a void `HashLabel` type.
why:
A `HashLabel` type is a pair `(root-vertex-ID, Keccak-hash)`. Previously,
a valid `HashLabel` consisted of a non-empty hash and a non-zero vertex
ID. This definition leads to a non-unique representation of a void
`HashLabel` with either root-ID or has void. This has been changed to
the unique void `HashLabel` exactly if the hash entry is void.
* Update consistency checkers
* Re-org `hashify()` procedure
why:
Syncing against block chain showed serious deficiencies which produced
wrong hashes or simply bailed out with error.
So all fringe cases (mainly due to deleted entries) could be integrated
into the labelling schedule rather than handling separate fringe cases.
* Fix debug noise in `hashify()` for perfectly normal situation
why:
Was previously considered a fixable error
* Fix test sample file names
why:
The larger test file `goerli68161.txt.gz` is already in the local
archive. So there is no need to use the smaller one from the external
repo.
* Activate `accounts_cache` module from `db/ledger`
why:
A copy of the original `accounts_cache.nim` source to be integrated
into the `Ledger` module wrapper which allows to switch between
different `accounts_cache` implementations unser tha same API.
details:
At a later state, the `db/accounts_cache.nim` wrapper will be
removed so that there is only one access to that module via
`db/ledger/accounts_cache.nim`.
* Fix copyright headers in source code
* Aristo: Provide key-value list signature calculator
detail:
Simple wrappers around `Aristo` core functionality
* Update new API for `CoreDb`
details:
+ Renamed new API functions `contains()` => `hasKey()` or `hasPath()`
which disables the `in` operator on non-boolean `contains()` functions
+ The functions `get()` and `fetch()` always return a not-found error if
there is no item, available. The new functions `getOrEmpty()` and
`mergeOrEmpty()` return an an empty `Blob` if there is no such key
found.
* Rewrite `core_apps.nim` using new API from `CoreDb`
* Use `Aristo` functionality for calculating Merkle signatures
details:
For debugging, the `VerifyAristoForMerkleRootCalc` can be set so
that `Aristo` results will be verified against the legacy versions.
* Provide general interface for Merkle signing key-value tables
details:
Export `Aristo` wrappers
* Activate `CoreDb` tests
why:
Now, API seems to be stable enough for general tests.
* Update `toHex()` usage
why:
Byteutils' `toHex()` is superior to `toSeq.mapIt(it.toHex(2)).join`
* Split `aristo_transcode` => `aristo_serialise` + `aristo_blobify`
why:
+ Different modules for different purposes
+ `aristo_serialise`: RLP encoding/decoding
+ `aristo_blobify`: Aristo database encoding/decoding
* Compacted representation of small nodes' links instead of Keccak hashes
why:
Ethereum MPTs use Keccak hashes as node links if the size of an RLP
encoded node is at least 32 bytes. Otherwise, the RLP encoded node
value is used as a pseudo node link (rather than a hash.) Such a node
is nor stored on key-value database. Rather the RLP encoded node value
is stored instead of a lode link in a parent node instead. Only for
the root hash, the top level node is always referred to by the hash.
This feature needed an abstraction of the `HashKey` object which is now
either a hash or a blob of length at most 31 bytes. This leaves two
ways of representing an empty/void `HashKey` type, either as an empty
blob of zero length, or the hash of an empty blob.
* Update `CoreDb` interface (mainly reducing logger noise)
* Fix copyright years (to make `Lint` happy)
* Update docu
* Update Aristo/Kvt constructor prototype
why:
Previous version used an `enum` value to indicate what backend is to
be used. This was replaced by using the backend object type.
* Rewrite `hikeUp()` return code into `Result[Hike,(Hike,AristoError)]`
why:
Better code maintenance. Previously, the `Hike` object was returned. It
had an internal error field so partial success was also available on
a failure. This error field has been removed.
* Use `openArray[byte]` rather than `Blob` in functions prototypes
* Provide synchronised multi instance transactions
why:
The `CoreDB` object was geared towards the legacy DB which used a single
transaction for the key-value backend DB. Different state roots are
provided by the backend database, so all instances work directly on the
same backend.
Aristo db instances have different in-memory mappings (aka different
state roots) and the transactions are on top of there mappings. So each
instance might run different transactions.
Multi instance transactions are a compromise to converge towards the
legacy behaviour. The synchronised transactions span over all instances
available at the time when base transaction was opened. Instances
created later are unaffected.
* Provide key-value pair database iterator
why:
Needed in `CoreDB` for `replicate()` emulation
also:
Some update of internal code
* Extend API (i.e. prototype variants)
why:
Needed for `CoreDB` geared towards the legacy backend which has a more
basic API than Aristo.
* Rewrite remaining `AristoError` return code into `Result[void,AristoError]`
why:
Better code maintenance
* Update import sections
* Update Aristo DB paths
why:
More systematic so directory can be shared with other DB types
* More cosmetcs
* Update unit tests runners
why:
Proper handling of persistent and mem-only DB. The latter can be
consistently triggered by an empty DB path.
* Reorg of distributed backend access
details:
Now handled via API provided in `aristo_desc`.
* Rename `checkCache()` => `checkTop()`
why:
Better naming for top layer cache checker
also:
Provide cascaded fifos checker
* Provide `eq` directive for finding filter by exact filter ID (think block number)
* Some code beautification (for better code reading)
* State root reposition and reorg
details:
Repositioning is supported by forking a new descriptor. Reorg is then
accomplished by writing this forked state on the backend database.
* Removed dedicated transcoder tests
why:
will implicitely be provided by other tests:
+ encode/write -> hashify -> test_tx
+ decode/read -> merge raw nodes -> test_tx
+ de/blobfiy -> backend operations, taext_tx, test_backend, test_filter
* Clarify how the vertex ID generator state is accessed from the backend
why:
This state is a list of unused vertex IDs. It was just stored somewhere
on the backend which details were exposed when iterating over some
sub-table(s).
As there will be more such single information records, an admin
sub-tables has been defined (formerly ID generator table) with dedicated
access keys and type. Also, the iterator over the single ID generator
state item has been removed. It must be accessed via the `get()`
interface.
* Remove trailing space from file name
why:
fixes windows bail out
* Fix hashing algorithm
why:
Particular case where a sub-tree is on the backend, linked by an
Extension vertex to the top level.
* Update backend verification to report `dirty` top layer
* Implement distributed merge of backend filters
* Implement distributed backend access management
details:
Implemented and tested as described in chapter 5 of the `README.md`
file.
* Renamed type `NoneBackendRef` => `VoidBackendRef`
* Clarify names: `BE=filter+backend` and `UBE=backend (unfiltered)`
why:
Most functions used full names as `getVtxUnfilteredBackend()` or
`getKeyBackend()`. After defining abbreviations (and its meaning) it
seems easier to use `getVtxUBE()` and `getKeyBE()`.
* Integrate `hashify()` process into transaction logic
why:
Is now transparent unless explicitly controlled.
details:
Cache changes imply setting a `dirty` flag which in turn triggers
`hashify()` processing in transaction and `pack()` directives.
* Removed `aristo_tx.exec()` directive
why:
Inconsistent implementation, functionality will be provided with a
different paradigm.
* Provide deep copy for each transaction layer
why:
Localising changes. Selective deep copy was just overlooked.
* Generalise vertex ID generator state reorg function `vidReorg()`
why:
makes it somewhat easier to handle when saving layers.
* Provide dummy back end descriptor `NoneBackendRef`
* Optional read-only filter between backend and transaction cache
why:
Some staging area for accumulating changes to the backend DB. This
will eventually be an access layer for emulating a backend with
multiple/historic state roots.
* Re-factor `persistent()` with filter between backend/tx-cache => `stow()`
why:
The filter provides an abstraction from the physically stored data on
disk. So, there can be several MPT instances using the same disk data
with different state roots. Of course, all the MPT instances should
not differ too much for practical reasons :).
TODO:
Filter administration tools need to be provided.
* Misc fixes
detail:
* Fix de-serialisation for account leafs
* Update node recovery from unit tests
* Remove `LegacyAccount` from `PayloadRef` object
why:
Legacy accounts use a hash key as storage root which is detrimental
to the working of the Aristo database which uses a vertex ID.
* Dissolve `hashify_helper` into `aristo_utils` and `aristo_transcode`
why:
Functions are of general interest so they should live in first level
code files.
* Added left/right iterators over leaf nodes
* Some helper/wrapper functions that might be useful
why:
For the main tree with root vertex ID 1, the leaf nodes hold the
account data. These accounts may link to sub trees the storage root
node ID of which must be registered here. There is no reverse key
lookup on the backend.
note:
These definitions are experimental. Also, there are some tests missing
for validating Payload data conversions.
* Slightly tighten some self-check conditions
* Redefined the database descriptor object as reference (to the object)
why:
The upcoming transaction wrapper will work with a database reference
rather than the object itself
* Append state before `save()` to the Aristo descriptor
why:
This stae was previously returned by the function. Appending it to
a field of the Aristo descriptor seems easier to handle.
* Fix missing branch checks in transcoder
why:
Symmetry problem. `Blobify()` allowed for encoding degenerate branch
vertices while `Deblobify()` rejected decoding wrongly encoded data.
* Update memory backend so that it rejects storing bogus vertices.
why:
Error behaviour made similar to the rocks DB backend.
* Make sure that leaf vertex IDs are not repurposed
why:
This makes it easier to record leaf node changes
* Update error return code for next()/right() traversal
why:
Returning offending vertex ID (besides error code) helps debugging
* Update Merkle hasher for deleted nodes
why:
Not implemented, yet
also:
Provide cache & backend consistency check functions. This was
partly re-implemented from `hashifyCheck()`
* Simplify some unit tests
* Fix delete function
why:
Was conceptually wrong
Jacek Sieka
Jordan Hrycaj
andri lim