Dave Collins af3ed803f5 database: Major redesign of database package.

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.

Some of the reason for this were discussed in #255, however a quick
summary 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 bitcoin-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 bitcoin 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.

Finally, this commit addresses the following issues:

- Adds support for and therefore closes #255
- Fixes #199
- Fixes #201
- Implements and closes #256
- Obsoletes and closes #257
- Closes #247 once the required chain and btcd modifications are in place
  to make use of this new code

2016-02-03 11:42:04 -06:00

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database

[] (https://travis-ci.org/btcsuite/btcd)

Package database provides a block and metadata storage database.

Please note that this package is intended to enable btcd to support different database backends and is not something that a client can directly access as only one entity can have the database open at a time (for most database backends), and that entity will be btcd.

When a client wants programmatic access to the data provided by btcd, they'll likely want to use the btcrpcclient package which makes use of the [JSON-RPC API] (https://github.com/btcsuite/btcd/tree/master/docs/json_rpc_api.md).

However, this package could be extremely useful for any applications requiring Bitcoin block storage capabilities.

As of July 2015, there are over 365,000 blocks in the Bitcoin block chain and and over 76 million transactions (which turns out to be over 35GB of data). This package provides a database layer to store and retrieve this data in a simple and efficient manner.

The default backend, ffldb, has a strong focus on speed, efficiency, and robustness. It makes use of leveldb for the metadata, flat files for block storage, and strict checksums in key areas to ensure data integrity.

Feature Overview

Key/value metadata store
Bitcoin block storage
Efficient retrieval of block headers and regions (transactions, scripts, etc)
Read-only and read-write transactions with both manual and managed modes
Nested buckets
Iteration support including cursors with seek capability
Supports registration of backend databases
Comprehensive test coverage

Documentation

[] (http://godoc.org/github.com/btcsuite/btcd/database)

Full go doc style documentation for the project can be viewed online without installing this package by using the GoDoc site here: http://godoc.org/github.com/btcsuite/btcd/database

You can also view the documentation locally once the package is installed with the godoc tool by running godoc -http=":6060" and pointing your browser to http://localhost:6060/pkg/github.com/btcsuite/btcd/database

Installation

$ go get github.com/btcsuite/btcd/database

Examples

[Basic Usage Example] (http://godoc.org/github.com/btcsuite/btcd/database#example-package--BasicUsage)
Demonstrates creating a new database and using a managed read-write transaction to store and retrieve metadata.
[Block Storage and Retrieval Example] (http://godoc.org/github.com/btcsuite/btcd/database#example-package--BlockStorageAndRetrieval)
Demonstrates creating a new database, using a managed read-write transaction to store a block, and then using a managed read-only transaction to fetch the block.

License

Package database is licensed under the copyfree ISC License.

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