This commit adds commitQueue which is a lightweight contention manager
for STM transactions. The queue attempts to queue up transactions that
conflict for sequential execution, while leaving all "unblocked"
transactons to run freely in parallel.
In this commit, unify the old and new values for `sync-freelist`, and
also ensure that we don't break behavior for any users that're using the
_old_ value.
To do this, we first rename what was `--db.bolt.no-sync-freelist`, to
`--db.bolt.sync-freelist`. This gets rid of the negation on the config
level, and lets us override that value if the user is specifying the
legacy config option.
In the future, we'll deprecate the old config option, in favor of the
new DB scoped option.
This commit extends compatibility with the bbolt kvdb implementation,
which returns ErrIncompatibleValue in case of a bucket/value key
collision. Furthermore the commit also adds an extra precondition to the
transaction when a key doesn't exist. This is needed as we fix reads to
a snapshot revision and other writers may commit the key otherwise.
This commit removes the lock set which was used to only add bucket keys
to the tx predicate while also bumping their mod version.
This was useful to reduce the size of the compare set but wasn't useful
to reduce contention as top level buckets were always in the lock set.
This commit changes the key derivation algo we use to emulate buckets
similar to bbolt. The issue with prefixing keys with either a bucket or
a value prefix is that the cursor couldn't effectively iterate trough
all keys in a bucket, as it skipped the bucket keys.
While there are multiple ways to fix that issue (eg. two pointers,
iterating value keys then bucket keys, etc), the cleanest is to instead
of prefixes in keys we use a postfix indicating whether a key is a
bucket or a value. This also simplifies all operations where we
(recursively) iterate a bucket and is equivalent with the prefixing key
derivation with the addition that bucket and value keys are now
continous.
This commit extends the etcd.BackendConfig to also provide an abort
context and integrates it with the STM retry loop in order to be able
stop LND when conflicting transactions keep the loop running.
This commit removes the retry goroutine from the STM as the retry loop
is only running when the STM transaction is encapsulated in Update/View
whereas for self-standing transactions we use a different approach.
By removing the goroutine we won't catch panics thrown that are supposed
to be catched outside of the STM.
This commit extends etcd db with namespaces without additional storage
space requirements. This is simply done by instead of using an all zero
root bucket id, we use the sha256 hash of the name space as our root
bucket id.
This commit separates all etcd related sources (sans a few stubs and
config) from the rest of the source tree and makes compilation conditional
depending on whether the kvdb_etcd build tag is specified.
This commit adds the ExtendedBackend interface which is an extension to
the walletdb.DB interface. This paves the way to using etcd.db.View and
etcd.db.Update in the global View and Update functions without much code
rewrite.
This commit reduces the compare set size the STM will submit in
transactions by adding only the bucket keys along the bucket path to a
specific lock set. This lock set then used to filter the read set,
effectively removing all read only keys from the transaction predicate
that are not bucket keys.
By tracking if a read-write tx actually changes something, we can also
"bump" the mod revision of the bucket keys.
With this trick we essentially implement a read-write lock for our
bucket structure greatly reducing transaction processing time.
This commit adds an extended STM, similar to what available in etcd's
clientv3 module. This incarnation of said STM supports additional
features, like positioning in key intervals while taking into account
deletes and writes as well. This is a preliminary work to support all
features of the kvdb interface.
In this commit, we create a new package `kvdb`, which is meant to serve
as the basis for any future database abstractions within `lnd`. Rather
than directly use the `walletdb` package (which we base off of), we
instead use a series of type-aliases to re-type the fundamental
types/interfaces of the `walletdb` package. This lets us type
`kvdb.RwTx` instead of `walletdb.ReadWriteTransaction` everywhere.
Additionally, our usage of type-aliases is also intended to create an
easy pathway in the future wherein we can gradually re-defined or
re-implement these types to wean off of the `walletdb` package.
