4db689e691
This commit contains a complete redesign and rewrite of the database
package that approaches things in a vastly different manner than the
previous version. This is the first part of several stages that will be
needed to ultimately make use of this new package.
A quick summary of the changes is as follows:
- The previous database could only contain blocks on the main chain and
reorgs required deleting the blocks from the database. This made it
impossible to store orphans and could make external RPC calls for
information about blocks during the middle of a reorg fail.
- The previous database interface forced a high level of coin-specific
intelligence such as spend tracking into each backend driver.
- The aforementioned point led to making it difficult to implement new
backend drivers due to the need to repeat a lot of non-trivial logic
which is better handled at a higher layer, such as the blockchain
package.
- The old database stored all blocks in leveldb. This made it extremely
inefficient to do things such as lookup headers and individual
transactions since the entire block had to be loaded from leveldb (which
entails it doing data copies) to get access.
In order to address all of these concerns, and others not mentioned, the
database interface has been redesigned as follows:
- Two main categories of functionality are provided: block storage and
metadata storage
- All block storage and metadata storage are done via read-only and
read-write MVCC transactions with both manual and managed modes
- Support for multiple concurrent readers and a single writer
- Readers use a snapshot and therefore are not blocked by the writer
- Some key properties of the block storage and retrieval API:
- It is generic and does NOT contain additional coin logic such spend
tracking and block linking
- Provides access to the raw serialized bytes so deserialization is not
forced for callers that don't need it
- Support for fetching headers via independent functions which allows
implementations to provide significant optimizations
- Ability to efficiently retrieve arbitrary regions of blocks
(transactions, scripts, etc)
- A rich metadata storage API is provided:
- Key/value with arbitrary data
- Support for buckets and nested buckets
- Bucket iteration through a couple of different mechanisms
- Cursors for efficient and direct key seeking
- Supports registration of backend database implementations
- Comprehensive test coverage
- Provides strong documentation with example usage
This commit also contains an implementation of the previously discussed
interface named ffldb (flat file plus leveldb metadata backend). Here
is a quick overview:
- Highly optimized for read performance with consistent write performance
regardless of database size
- All blocks are stored in flat files on the file system
- Bulk block region fetching is optimized to perform linear reads which
improves performance on spindle disks
- Anti-corruption mechanisms:
- Flat files contain full block checksums to quickly an easily detect
database corruption without needing to do expensive merkle root
calculations
- Metadata checksums
- Open reconciliation
- Extensive test coverage:
- Comprehensive blackbox interface testing
- Whitebox testing which uses intimate knowledge to exercise uncommon
failure paths such as deleting files out from under the database
- Corruption tests (replacing random data in the files)
In addition, this commit also contains a new tool under the new database
directory named dbtool which provides a few basic commands for testing the
database. It is designed around commands, so it could be useful to expand
on in the future.
90 lines
3.0 KiB
Go
90 lines
3.0 KiB
Go
// Copyright (c) 2015-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package database2
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import (
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"fmt"
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"github.com/btcsuite/btclog"
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)
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// Driver defines a structure for backend drivers to use when they registered
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// themselves as a backend which implements the DB interface.
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type Driver struct {
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// DbType is the identifier used to uniquely identify a specific
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// database driver. There can be only one driver with the same name.
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DbType string
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// Create is the function that will be invoked with all user-specified
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// arguments to create the database. This function must return
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// ErrDbExists if the database already exists.
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Create func(args ...interface{}) (DB, error)
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// Open is the function that will be invoked with all user-specified
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// arguments to open the database. This function must return
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// ErrDbDoesNotExist if the database has not already been created.
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Open func(args ...interface{}) (DB, error)
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// UseLogger uses a specified Logger to output package logging info.
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UseLogger func(logger btclog.Logger)
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}
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// driverList holds all of the registered database backends.
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var drivers = make(map[string]*Driver)
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// RegisterDriver adds a backend database driver to available interfaces.
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// ErrDbTypeRegistered will be retruned if the database type for the driver has
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// already been registered.
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func RegisterDriver(driver Driver) error {
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if _, exists := drivers[driver.DbType]; exists {
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str := fmt.Sprintf("driver %q is already registered",
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driver.DbType)
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return makeError(ErrDbTypeRegistered, str, nil)
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}
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drivers[driver.DbType] = &driver
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return nil
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}
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// SupportedDrivers returns a slice of strings that represent the database
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// drivers that have been registered and are therefore supported.
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func SupportedDrivers() []string {
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supportedDBs := make([]string, 0, len(drivers))
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for _, drv := range drivers {
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supportedDBs = append(supportedDBs, drv.DbType)
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}
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return supportedDBs
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}
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// Create intializes and opens a database for the specified type. The arguments
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// are specific to the database type driver. See the documentation for the
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// database driver for further details.
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//
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// ErrDbUnknownType will be returned if the the database type is not registered.
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func Create(dbType string, args ...interface{}) (DB, error) {
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drv, exists := drivers[dbType]
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if !exists {
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str := fmt.Sprintf("driver %q is not registered", dbType)
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return nil, makeError(ErrDbUnknownType, str, nil)
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}
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return drv.Create(args...)
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}
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// Open opens an existing database for the specified type. The arguments are
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// specific to the database type driver. See the documentation for the database
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// driver for further details.
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//
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// ErrDbUnknownType will be returned if the the database type is not registered.
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func Open(dbType string, args ...interface{}) (DB, error) {
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drv, exists := drivers[dbType]
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if !exists {
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str := fmt.Sprintf("driver %q is not registered", dbType)
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return nil, makeError(ErrDbUnknownType, str, nil)
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}
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return drv.Open(args...)
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}
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