95a4f37e5c
Unlike vellum's MergeIterator, the enumerator introduced in this commit doesn't merge when there are matching keys across iterators. Instead, the enumerator implementation provides a traversal of all the tuples of (key, iteratorIndex, val) from the underlying vellum iterators, ordered by key ASC, iteratorIndex ASC.
125 lines
3.1 KiB
Go
125 lines
3.1 KiB
Go
// Copyright (c) 2018 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package zap
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import (
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"bytes"
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"github.com/couchbase/vellum"
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)
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// enumerator provides an ordered traversal of multiple vellum
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// iterators. Like JOIN of iterators, the enumerator produces a
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// sequence of (key, iteratorIndex, value) tuples, sorted by key ASC,
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// then iteratorIndex ASC, where the same key might be seen or
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// repeated across multiple child iterators.
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type enumerator struct {
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itrs []vellum.Iterator
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currKs [][]byte
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currVs []uint64
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lowK []byte
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lowIdxs []int
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lowCurr int
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}
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// newEnumerator returns a new enumerator over the vellum Iterators
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func newEnumerator(itrs []vellum.Iterator) (*enumerator, error) {
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rv := &enumerator{
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itrs: itrs,
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currKs: make([][]byte, len(itrs)),
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currVs: make([]uint64, len(itrs)),
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lowIdxs: make([]int, 0, len(itrs)),
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}
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for i, itr := range rv.itrs {
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rv.currKs[i], rv.currVs[i] = itr.Current()
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}
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rv.updateMatches()
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if rv.lowK == nil {
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return rv, vellum.ErrIteratorDone
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}
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return rv, nil
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}
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// updateMatches maintains the low key matches based on the currKs
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func (m *enumerator) updateMatches() {
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m.lowK = nil
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m.lowIdxs = m.lowIdxs[:0]
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m.lowCurr = 0
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for i, key := range m.currKs {
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if key == nil {
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continue
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}
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cmp := bytes.Compare(key, m.lowK)
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if cmp < 0 || m.lowK == nil {
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// reached a new low
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m.lowK = key
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m.lowIdxs = m.lowIdxs[:0]
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m.lowIdxs = append(m.lowIdxs, i)
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} else if cmp == 0 {
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m.lowIdxs = append(m.lowIdxs, i)
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}
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}
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}
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// Current returns the enumerator's current key, iterator-index, and
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// value. If the enumerator is not pointing at a valid value (because
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// Next returned an error previously), Current will return nil,0,0.
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func (m *enumerator) Current() ([]byte, int, uint64) {
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var i int
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var v uint64
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if m.lowCurr < len(m.lowIdxs) {
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i = m.lowIdxs[m.lowCurr]
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v = m.currVs[i]
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}
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return m.lowK, i, v
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}
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// Next advances the enumerator to the next key/iterator/value result,
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// else vellum.ErrIteratorDone is returned.
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func (m *enumerator) Next() error {
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m.lowCurr += 1
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if m.lowCurr >= len(m.lowIdxs) {
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// move all the current low iterators forwards
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for _, vi := range m.lowIdxs {
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err := m.itrs[vi].Next()
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if err != nil && err != vellum.ErrIteratorDone {
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return err
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}
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m.currKs[vi], m.currVs[vi] = m.itrs[vi].Current()
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}
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m.updateMatches()
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}
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if m.lowK == nil {
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return vellum.ErrIteratorDone
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}
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return nil
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}
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// Close all the underlying Iterators. The first error, if any, will
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// be returned.
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func (m *enumerator) Close() error {
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var rv error
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for _, itr := range m.itrs {
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err := itr.Close()
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if rv == nil {
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rv = err
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}
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}
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return rv
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}
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