af3ed803f5
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
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treap
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(https://travis-ci.org/btcsuite/btcd)
Package treap implements a treap data structure that is used to hold ordered key/value pairs using a combination of binary search tree and heap semantics. It is a self-organizing and randomized data structure that doesn't require complex operations to to maintain balance. Search, insert, and delete operations are all O(log n). Both mutable and immutable variants are provided.
The mutable variant is typically faster since it is able to simply update the treap when modifications are made. However, a mutable treap is not safe for concurrent access without careful use of locking by the caller and care must be taken when iterating since it can change out from under the iterator.
The immutable variant works by creating a new version of the treap for all mutations by replacing modified nodes with new nodes that have updated values while sharing all unmodified nodes with the previous version. This is extremely useful in concurrent applications since the caller only has to atomically replace the treap pointer with the newly returned version after performing any mutations. All readers can simply use their existing pointer as a snapshot since the treap it points to is immutable. This effectively provides O(1) snapshot capability with efficient memory usage characteristics since the old nodes only remain allocated until there are no longer any references to them.
Package treap is licensed under the copyfree ISC license.
Usage
This package is only used internally in the database code and as such is not available for use outside of it.
Documentation
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(http://godoc.org/github.com/btcsuite/btcd/database/internal/treap)
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/internal/treap
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/internal/treap
License
Package treap is licensed under the copyfree ISC License.