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walletdb: add View and Update to DB interface

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We want to make sure that every database backend has their own
implementation of the View() and Update() methods to make sure any
custom retry/commit/rollback strategies are used even when invoked
through the package-provided View() and Update() functions.
This commit is contained in:
Oliver Gugger 2021-07-19 13:33:20 +02:00
parent f07fdfb6b9
commit a27bab6eb9
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GPG key ID: 8E4256593F177720
2 changed files with 121 additions and 49 deletions
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77
walletdb/bdb/db.go
View file

@ -365,6 +365,83 @@ func (db *db) Batch(f func(tx walletdb.ReadWriteTx) error) error {
})
}
// View opens a database read transaction and executes the function f with the
// transaction passed as a parameter. After f exits, the transaction is rolled
// back. If f errors, its error is returned, not a rollback error (if any
// occur). The passed reset function is called before the start of the
// transaction and can be used to reset intermediate state. As callers may
// expect retries of the f closure (depending on the database backend used), the
// reset function will be called before each retry respectively.
func (db *db) View(f func(tx walletdb.ReadTx) error, reset func()) error {
// We don't do any retries with bolt so we just initially call the reset
// function once.
reset()
tx, err := db.BeginReadTx()
if err != nil {
return err
}
// Make sure the transaction rolls back in the event of a panic.
defer func() {
if tx != nil {
_ = tx.Rollback()
}
}()
err = f(tx)
rollbackErr := tx.Rollback()
if err != nil {
return err
}
if rollbackErr != nil {
return rollbackErr
}
return nil
}
// Update opens a database read/write transaction and executes the function f
// with the transaction passed as a parameter. After f exits, if f did not
// error, the transaction is committed. Otherwise, if f did error, the
// transaction is rolled back. If the rollback fails, the original error
// returned by f is still returned. If the commit fails, the commit error is
// returned. As callers may expect retries of the f closure (depending on the
// database backend used), the reset function will be called before each retry
// respectively.
func (db *db) Update(f func(tx walletdb.ReadWriteTx) error, reset func()) error {
// We don't do any retries with bolt so we just initially call the reset
// function once.
reset()
tx, err := db.BeginReadWriteTx()
if err != nil {
return err
}
// Make sure the transaction rolls back in the event of a panic.
defer func() {
if tx != nil {
_ = tx.Rollback()
}
}()
err = f(tx)
if err != nil {
// Want to return the original error, not a rollback error if
// any occur.
_ = tx.Rollback()
return err
}
return tx.Commit()
}
// PrintStats returns all collected stats pretty printed into a string.
func (db *db) PrintStats() string {
return "<no stats are collected by bdb backend>"
}
// filesExists reports whether the named file or directory exists.
func fileExists(name string) bool {
if _, err := os.Stat(name); err != nil {

93
walletdb/interface.go
View file

@ -126,8 +126,9 @@ type ReadWriteBucket interface {
// ErrTxNotWritable if attempted against a read-only transaction.
Delete(key []byte) error
// Cursor returns a new cursor, allowing for iteration over the bucket's
// key/value pairs and nested buckets in forward or backward order.
// ReadWriteCursor returns a new cursor, allowing for iteration over the
// bucket's key/value pairs and nested buckets in forward or backward
// order.
ReadWriteCursor() ReadWriteCursor
// Tx returns the bucket's transaction.
@ -190,7 +191,7 @@ func BucketIsEmpty(bucket ReadBucket) bool {
return k == nil && v == nil
}
// DB represents an ACID database. All database access is performed through
// DB represents an ACID database. All database access is performed through
// read or read+write transactions.
type DB interface {
// BeginReadTx opens a database read transaction.
@ -205,16 +206,45 @@ type DB interface {
// Close cleanly shuts down the database and syncs all data.
Close() error
// PrintStats returns all collected stats pretty printed into a string.
PrintStats() string
// View opens a database read transaction and executes the function f
// with the transaction passed as a parameter. After f exits, the
// transaction is rolled back. If f errors, its error is returned, not a
// rollback error (if any occur). The passed reset function is called
// before the start of the transaction and can be used to reset
// intermediate state. As callers may expect retries of the f closure
// (depending on the database backend used), the reset function will be
// called before each retry respectively.
//
// NOTE: For new code, this method should be used directly instead of
// the package level View() function.
View(f func(tx ReadTx) error, reset func()) error
// Update opens a database read/write transaction and executes the
// function f with the transaction passed as a parameter. After f exits,
// if f did not error, the transaction is committed. Otherwise, if f did
// error, the transaction is rolled back. If the rollback fails, the
// original error returned by f is still returned. If the commit fails,
// the commit error is returned. As callers may expect retries of the f
// closure (depending on the database backend used), the reset function
// will be called before each retry respectively.
//
// NOTE: For new code, this method should be used directly instead of
// the package level Update() function.
Update(f func(tx ReadWriteTx) error, reset func()) error
}
// BatchDB is a special version of the main DB interface that allos the caller
// to specify write transactions that should be combine dtoegether if multiple
// BatchDB is a special version of the main DB interface that allows the caller
// to specify write transactions that should be combined toegether if multiple
// goroutines are calling the Batch method.
type BatchDB interface {
DB
// Batch is similar to the package-level Update method, but it will
// attempt to optismitcally combine the invocation of several
// attempt to optimistically combine the invocation of several
// transaction functions into a single db write transaction.
Batch(func(tx ReadWriteTx) error) error
}
@ -223,29 +253,11 @@ type BatchDB interface {
// transaction passed as a parameter. After f exits, the transaction is rolled
// back. If f errors, its error is returned, not a rollback error (if any
// occur).
//
// NOTE: For new code the database backend's View method should be used directly
// as this package level function will be phased out in the future.
func View(db DB, f func(tx ReadTx) error) error {
tx, err := db.BeginReadTx()
if err != nil {
return err
}
// Make sure the transaction rolls back in the event of a panic.
defer func() {
if tx != nil {
tx.Rollback()
}
}()
err = f(tx)
rollbackErr := tx.Rollback()
if err != nil {
return err
}
if rollbackErr != nil {
return rollbackErr
}
return nil
return db.View(f, func() {})
}
// Update opens a database read/write transaction and executes the function f
@ -254,28 +266,11 @@ func View(db DB, f func(tx ReadTx) error) error {
// transaction is rolled back. If the rollback fails, the original error
// returned by f is still returned. If the commit fails, the commit error is
// returned.
//
// NOTE: For new code the database backend's Update method should be used
// directly as this package level function will be phased out in the future.
func Update(db DB, f func(tx ReadWriteTx) error) error {
tx, err := db.BeginReadWriteTx()
if err != nil {
return err
}
// Make sure the transaction rolls back in the event of a panic.
defer func() {
if tx != nil {
tx.Rollback()
}
}()
err = f(tx)
if err != nil {
// Want to return the original error, not a rollback error if
// any occur.
_ = tx.Rollback()
return err
}
return tx.Commit()
return db.Update(f, func() {})
}
// Batch opens a database read/write transaction and executes the function f