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backupccl: create and use readAsOfIterator in RESTORE
Previously while ingesting SSTs in the restore processor, `processRestoreSpanEntry` would manually skip delete tombstones and keys with timestamps later than the AS OF SYSTEM TIME timestamp provided in the RESTORE command. This PR wraps the restore processor's iterator with a new readAsOfIterator which abstracts this logic away. The readAsOfIterator wraps a SimpleMVCCIterator ond only surfaces the latest valid key of a given MVCC key that is also below the iterator's AOST timestamp, if set. Further, the iterator does not surface delete tombstones, nor any MVCC keys shadowed by delete tombstones below the AOST timestamp, if set. Fixes #77276 Release note: None
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2022 The Cockroach Authors. | ||
| // | ||
| // Use of this software is governed by the Business Source License | ||
| // included in the file licenses/BSL.txt. | ||
| // | ||
| // As of the Change Date specified in that file, in accordance with | ||
| // the Business Source License, use of this software will be governed | ||
| // by the Apache License, Version 2.0, included in the file | ||
| // licenses/APL.txt. | ||
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| package storage | ||
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| import "github.com/cockroachdb/cockroach/pkg/util/hlc" | ||
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| // ReadAsOfIterator wraps a SimpleMVCCIterator and only surfaces the latest | ||
| // valid key of a given MVCC key that is also below the asOf timestamp, if set. | ||
| // Further, the iterator does not surface delete tombstones, nor any MVCC keys | ||
| // shadowed by delete tombstones below the asOf timestamp, if set. The iterator | ||
| // assumes that it will not encounter any write intents. | ||
| type ReadAsOfIterator struct { | ||
| iter SimpleMVCCIterator | ||
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| // asOf is the latest timestamp of a key surfaced by the iterator. | ||
| asOf hlc.Timestamp | ||
| } | ||
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| var _ SimpleMVCCIterator = &ReadAsOfIterator{} | ||
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| // Close closes the underlying iterator. | ||
| func (f *ReadAsOfIterator) Close() { | ||
| f.iter.Close() | ||
| } | ||
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| // SeekGE advances the iterator to the first key in the engine which is >= the | ||
| // provided key that obeys the ReadAsOfIterator key constraints. | ||
| func (f *ReadAsOfIterator) SeekGE(originalKey MVCCKey) { | ||
| // To ensure SeekGE seeks to a key that isn't shadowed by a tombstone that the | ||
| // ReadAsOfIterator would have skipped (i.e. a tombstone below asOf), seek to | ||
| // the key with the latest possible timestamp that the iterator could surface | ||
| // (i.e. asOf, if set) and iterate to the next valid key at or below the caller's | ||
| // key that also obeys the iterator's constraints. | ||
| synthetic := MVCCKey{Key: originalKey.Key, Timestamp: f.asOf} | ||
| f.iter.SeekGE(synthetic) | ||
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| if ok := f.advance(); ok && f.UnsafeKey().Less(originalKey) { | ||
| // The following is true: | ||
| // originalKey.Key == f.UnsafeKey && | ||
| // f.asOf timestamp (if set) >= current timestamp > originalKey timestamp. | ||
| // | ||
| // This implies the caller is seeking to a key that is shadowed by a valid | ||
| // key that obeys the iterator 's constraints. The caller's key is NOT the | ||
| // latest key of the given MVCC key; therefore, skip to the next MVCC key. | ||
| f.NextKey() | ||
| } | ||
| } | ||
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| // Valid implements the simpleMVCCIterator. | ||
| func (f *ReadAsOfIterator) Valid() (bool, error) { | ||
| return f.iter.Valid() | ||
| } | ||
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| // Next advances the iterator to the next valid MVCC key obeying the iterator's | ||
| // constraints. Note that Next and NextKey have the same implementation because | ||
| // the iterator only surfaces the latest valid key of a given MVCC key below the | ||
| // asOf timestamp. | ||
| func (f *ReadAsOfIterator) Next() { | ||
| f.NextKey() | ||
| } | ||
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| // NextKey advances the iterator to the next valid MVCC key obeying the | ||
| // iterator's constraints. NextKey() is only guaranteed to surface a key that | ||
| // obeys the iterator's constraints if the iterator was already on a key that | ||
| // obeys the constraints. To ensure this, initialize the iterator with a SeekGE | ||
| // call before any calls to NextKey(). | ||
| func (f *ReadAsOfIterator) NextKey() { | ||
| f.iter.NextKey() | ||
| f.advance() | ||
| } | ||
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| // UnsafeKey returns the current key, but the memory is invalidated on the next | ||
| // call to {NextKey,Seek}. | ||
| func (f *ReadAsOfIterator) UnsafeKey() MVCCKey { | ||
| return f.iter.UnsafeKey() | ||
| } | ||
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| // UnsafeValue returns the current value as a byte slice, but the memory is | ||
| // invalidated on the next call to {NextKey,Seek}. | ||
| func (f *ReadAsOfIterator) UnsafeValue() []byte { | ||
| return f.iter.UnsafeValue() | ||
| } | ||
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| // advance moves past keys with timestamps later than f.asOf and skips MVCC keys | ||
| // whose latest value (subject to f.asOF) has been deleted. Note that advance | ||
| // moves past keys above asOF before evaluating tombstones, implying the | ||
| // iterator will never call f.iter.NextKey() on a tombstone with a timestamp | ||
| // later than f.asOF. | ||
| func (f *ReadAsOfIterator) advance() bool { | ||
| for { | ||
| if ok, err := f.Valid(); err != nil || !ok { | ||
| // No valid keys found. | ||
| return false | ||
| } else if !f.asOf.IsEmpty() && f.asOf.Less(f.iter.UnsafeKey().Timestamp) { | ||
| // Skip keys above the asOf timestamp. | ||
| f.iter.Next() | ||
| } else if len(f.iter.UnsafeValue()) == 0 { | ||
| // Skip to the next MVCC key if we find a tombstone. | ||
| f.iter.NextKey() | ||
| } else { | ||
| // On a valid key. | ||
| return true | ||
| } | ||
| } | ||
| } | ||
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| // NewReadAsOfIterator constructs a ReadAsOfIterator. | ||
| func NewReadAsOfIterator(iter SimpleMVCCIterator, asOf hlc.Timestamp) *ReadAsOfIterator { | ||
| return &ReadAsOfIterator{iter: iter, asOf: asOf} | ||
| } |
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