98 lines
2.3 KiB
Go
98 lines
2.3 KiB
Go
// Package memdb provides an in-memory database that supports transactions
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// and MVCC.
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package memdb
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import (
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"sync"
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"sync/atomic"
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"unsafe"
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"github.com/hashicorp/go-immutable-radix"
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)
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// MemDB is an in-memory database.
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//
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// MemDB provides a table abstraction to store objects (rows) with multiple
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// indexes based on inserted values. The database makes use of immutable radix
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// trees to provide transactions and MVCC.
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type MemDB struct {
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schema *DBSchema
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root unsafe.Pointer // *iradix.Tree underneath
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primary bool
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// There can only be a single writer at once
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writer sync.Mutex
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}
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// NewMemDB creates a new MemDB with the given schema
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func NewMemDB(schema *DBSchema) (*MemDB, error) {
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// Validate the schema
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if err := schema.Validate(); err != nil {
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return nil, err
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}
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// Create the MemDB
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db := &MemDB{
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schema: schema,
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root: unsafe.Pointer(iradix.New()),
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primary: true,
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}
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if err := db.initialize(); err != nil {
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return nil, err
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}
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return db, nil
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}
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// getRoot is used to do an atomic load of the root pointer
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func (db *MemDB) getRoot() *iradix.Tree {
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root := (*iradix.Tree)(atomic.LoadPointer(&db.root))
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return root
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}
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// Txn is used to start a new transaction, in either read or write mode.
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// There can only be a single concurrent writer, but any number of readers.
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func (db *MemDB) Txn(write bool) *Txn {
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if write {
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db.writer.Lock()
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}
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txn := &Txn{
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db: db,
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write: write,
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rootTxn: db.getRoot().Txn(),
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}
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return txn
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}
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// Snapshot is used to capture a point-in-time snapshot
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// of the database that will not be affected by any write
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// operations to the existing DB.
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func (db *MemDB) Snapshot() *MemDB {
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clone := &MemDB{
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schema: db.schema,
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root: unsafe.Pointer(db.getRoot()),
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primary: false,
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}
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return clone
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}
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// initialize is used to setup the DB for use after creation. This should
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// be called only once after allocating a MemDB.
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func (db *MemDB) initialize() error {
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root := db.getRoot()
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for tName, tableSchema := range db.schema.Tables {
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for iName := range tableSchema.Indexes {
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index := iradix.New()
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path := indexPath(tName, iName)
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root, _, _ = root.Insert(path, index)
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}
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}
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db.root = unsafe.Pointer(root)
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return nil
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}
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// indexPath returns the path from the root to the given table index
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func indexPath(table, index string) []byte {
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return []byte(table + "." + index)
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}
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