/
db.go
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/
db.go
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// SPDX-License-Identifier: Apache-2.0
// Copyright Authors of Cilium
package statedb
import (
"context"
"net/http"
"runtime"
"slices"
"sort"
"sync"
"sync/atomic"
"time"
"github.com/cilium/statedb/internal"
)
// DB provides an in-memory transaction database built on top of immutable radix
// trees. The database supports multiple tables, each with one or more user-defined
// indexes. Readers can access the data locklessly with a simple atomic pointer read
// to obtain a snapshot. On writes to the database table-level locks are acquired
// on target tables and on write transaction commit a root lock is taken to swap
// in the new root with the modified tables.
//
// As data is stored in immutable data structures any objects inserted into
// it MUST NOT be mutated afterwards.
//
// DB holds the "root" tree of tables with each table holding a tree of indexes:
//
// root
// / \
// ba T(foo)
// / \
// T(bar) T(baz)
//
// T(bar).indexes
// / \
// i I(byRevision)
// / \
// I(id) I(ip)
//
// I(ip)
// / \
// 192 172
// / ...
// bar(192.168.1.1)
//
// T = tableEntry
// I = indexTree
//
// To lookup:
// 1. Create a read (or write) transaction
// 2. Find the table from the root tree
// 3. Find the index from the table's index tree
// 4. Find the object from the index
//
// To insert:
// 1. Create write transaction against the target table
// 2. Find the table from the root tree
// 3. Create/reuse write transaction on primary index
// 4. Insert/replace the object into primary index
// 5. Create/reuse write transaction on revision index
// 6. If old object existed, remove from revision index
// 7. If old object existed, remove from graveyard
// 8. Update each secondary index
// 9. Commit transaction by committing each index to
// the table and then committing table to the root.
// Swap the root atomic pointer to new root and
// notify by closing channels of all modified nodes.
//
// To observe deletions:
// 1. Create write transaction against the target table
// 2. Create new delete tracker and add it to the table
// 3. Commit the write transaction to update the table
// with the new delete tracker
// 4. Query the graveyard by revision, starting from the
// revision of the write transaction at which it was
// created.
// 5. For each successfully processed deletion, mark the
// revision to set low watermark for garbage collection.
// 6. Periodically garbage collect the graveyard by finding
// the lowest revision of all delete trackers.
type DB struct {
mu sync.Mutex // protects 'tables' and sequences modifications to the root tree
ctx context.Context
cancel context.CancelFunc
root atomic.Pointer[dbRoot]
gcTrigger chan struct{} // trigger for graveyard garbage collection
gcExited chan struct{}
gcRateLimitInterval time.Duration
metrics Metrics
defaultHandle Handle
}
type dbRoot = []tableEntry
type Option func(*opts)
type opts struct {
metrics Metrics
}
func WithMetrics(m Metrics) Option {
return func(o *opts) {
o.metrics = m
}
}
// New creates a new database.
//
// The created database must be started and stopped!
func New(options ...Option) *DB {
var opts opts
for _, o := range options {
o(&opts)
}
if opts.metrics == nil {
// Use the default metrics implementation but don't publish it.
opts.metrics = NewExpVarMetrics(false)
}
db := &DB{
metrics: opts.metrics,
gcRateLimitInterval: defaultGCRateLimitInterval,
}
db.defaultHandle = Handle{db, "DB"}
root := dbRoot{}
db.root.Store(&root)
return db
}
// RegisterTable registers a table to the database:
//
// func NewMyTable() statedb.RWTable[MyTable] { ... }
// cell.Provide(NewMyTable),
// cell.Invoke(statedb.RegisterTable[MyTable]),
func RegisterTable[Obj any](db *DB, table RWTable[Obj]) error {
return db.RegisterTable(table)
}
// RegisterTable registers a table to the database.
func (db *DB) RegisterTable(table TableMeta, tables ...TableMeta) error {
db.mu.Lock()
defer db.mu.Unlock()
root := slices.Clone(*db.root.Load())
if err := db.registerTable(table, &root); err != nil {
return err
}
for _, t := range tables {
if err := db.registerTable(t, &root); err != nil {
return err
}
}
db.root.Store(&root)
return nil
}
func (db *DB) registerTable(table TableMeta, root *dbRoot) error {
name := table.Name()
for _, t := range *root {
if t.meta.Name() == name {
return tableError(name, ErrDuplicateTable)
}
}
pos := len(*root)
table.setTablePos(pos)
*root = append(*root, table.tableEntry())
return nil
}
// ReadTxn constructs a new read transaction for performing reads against
// a snapshot of the database.
//
// The returned ReadTxn is not thread-safe.
func (db *DB) ReadTxn() ReadTxn {
return db.defaultHandle.ReadTxn()
}
// WriteTxn constructs a new write transaction against the given set of tables.
// Each table is locked, which may block until the table locks are acquired.
// The modifications performed in the write transaction are not visible outside
// it until Commit() is called. To discard the changes call Abort().
//
// The returned WriteTxn is not thread-safe.
func (db *DB) WriteTxn(table TableMeta, tables ...TableMeta) WriteTxn {
return db.defaultHandle.WriteTxn(table, tables...)
}
// Start the background workers for the database.
//
// This starts the graveyard worker that deals with garbage collecting
// deleted objects that are no longer necessary for Changes().
func (db *DB) Start() error {
db.gcTrigger = make(chan struct{}, 1)
db.gcExited = make(chan struct{})
db.ctx, db.cancel = context.WithCancel(context.Background())
go graveyardWorker(db, db.ctx, db.gcRateLimitInterval)
return nil
}
// Stop the background workers.
func (db *DB) Stop() error {
db.cancel()
<-db.gcExited
return nil
}
// ServeHTTP is an HTTP handler for dumping StateDB as JSON.
//
// Example usage:
//
// var db *statedb.DB
//
// http.Handle("/db", db)
// http.ListenAndServe(":8080", nil)
func (db *DB) ServeHTTP(w http.ResponseWriter, r *http.Request) {
w.Header().Add("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
db.ReadTxn().WriteJSON(w)
}
// setGCRateLimitInterval can set the graveyard GC interval before DB is started.
// Used by tests.
func (db *DB) setGCRateLimitInterval(interval time.Duration) {
db.gcRateLimitInterval = interval
}
// NewHandle returns a named handle to the DB. The handle has the same ReadTxn and
// WriteTxn methods as DB, but annotated with the given name for more accurate
// cost accounting in e.g. metrics.
func (db *DB) NewHandle(name string) Handle {
return Handle{db, name}
}
// Handle is a named handle to the database for constructing read or write
// transactions.
type Handle struct {
db *DB
name string
}
func (h Handle) WriteTxn(table TableMeta, tables ...TableMeta) WriteTxn {
db := h.db
allTables := append(tables, table)
smus := internal.SortableMutexes{}
for _, table := range allTables {
smus = append(smus, table.sortableMutex())
}
lockAt := time.Now()
smus.Lock()
acquiredAt := time.Now()
root := *db.root.Load()
tableEntries := make([]*tableEntry, len(root))
var tableNames []string
for _, table := range allTables {
tableEntry := root[table.tablePos()]
tableEntry.indexes = slices.Clone(tableEntry.indexes)
tableEntries[table.tablePos()] = &tableEntry
tableNames = append(tableNames, table.Name())
db.metrics.WriteTxnTableAcquisition(
h.name,
table.Name(),
table.sortableMutex().AcquireDuration(),
)
}
// Sort the table names so they always appear ordered in metrics.
sort.Strings(tableNames)
db.metrics.WriteTxnTotalAcquisition(
h.name,
tableNames,
acquiredAt.Sub(lockAt),
)
txn := &txn{
db: db,
root: root,
modifiedTables: tableEntries,
smus: smus,
acquiredAt: acquiredAt,
tableNames: tableNames,
handle: h.name,
}
runtime.SetFinalizer(txn, txnFinalizer)
return txn
}
// ReadTxn constructs a new read transaction for performing reads against
// a snapshot of the database.
//
// The returned ReadTxn is not thread-safe.
func (h Handle) ReadTxn() ReadTxn {
return &txn{
db: h.db,
root: *h.db.root.Load(),
}
}