mirror of https://github.com/etcd-io/bbolt.git
109 lines
2.8 KiB
Go
109 lines
2.8 KiB
Go
package bolt
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// Transaction represents a read-only transaction on the database.
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// It can be used for retrieving values for keys as well as creating cursors for
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// iterating over the data.
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//
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// IMPORTANT: You must close transactions when you are done with them. Pages
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// can not be reclaimed by the writer until no more transactions are using them.
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// A long running read transaction can cause the database to quickly grow.
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type Transaction struct {
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db *DB
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meta *meta
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buckets *buckets
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pages map[pgid]*page
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}
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// txnid represents the internal transaction identifier.
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type txnid uint64
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// init initializes the transaction and associates it with a database.
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func (t *Transaction) init(db *DB) {
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t.db = db
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t.pages = nil
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// Copy the meta page since it can be changed by the writer.
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t.meta = &meta{}
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db.meta().copy(t.meta)
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// Read in the buckets page.
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t.buckets = &buckets{}
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t.buckets.read(t.page(t.meta.buckets))
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}
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// id returns the transaction id.
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func (t *Transaction) id() txnid {
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return t.meta.txnid
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}
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// Close closes the transaction and releases any pages it is using.
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func (t *Transaction) Close() {
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t.db.removeTransaction(t)
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}
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// DB returns a reference to the database that created the transaction.
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func (t *Transaction) DB() *DB {
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return t.db
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}
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// Bucket retrieves a bucket by name.
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// Returns nil if the bucket does not exist.
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func (t *Transaction) Bucket(name string) *Bucket {
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b := t.buckets.get(name)
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if b == nil {
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return nil
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}
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return &Bucket{
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bucket: b,
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name: name,
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transaction: t,
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}
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}
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// Buckets retrieves a list of all buckets.
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func (t *Transaction) Buckets() []*Bucket {
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buckets := make([]*Bucket, 0, len(t.buckets.items))
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for name, b := range t.buckets.items {
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bucket := &Bucket{bucket: b, transaction: t, name: name}
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buckets = append(buckets, bucket)
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}
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return buckets
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}
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// Cursor creates a cursor associated with a given bucket.
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// The cursor is only valid as long as the Transaction is open.
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// Do not use a cursor after the transaction is closed.
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func (t *Transaction) Cursor(name string) (*Cursor, error) {
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b := t.Bucket(name)
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if b == nil {
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return nil, ErrBucketNotFound
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}
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return b.cursor(), nil
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}
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// Get retrieves the value for a key in a named bucket.
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// Returns a nil value if the key does not exist.
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// Returns an error if the bucket does not exist.
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func (t *Transaction) Get(name string, key []byte) (value []byte, err error) {
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c, err := t.Cursor(name)
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if err != nil {
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return nil, err
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}
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return c.Get(key), nil
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}
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// page returns a reference to the page with a given id.
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// If page has been written to then a temporary bufferred page is returned.
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func (t *Transaction) page(id pgid) *page {
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// Check the dirty pages first.
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if t.pages != nil {
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if p, ok := t.pages[id]; ok {
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return p
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}
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}
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// Otherwise return directly from the mmap.
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return t.db.page(id)
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}
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