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storage: add MVCCExportFingerprint method and fingerprintWriter
This change introduces a fingerprintWriter that hashes every key/timestamp and value for point keys, and combines their hashes via a XOR into a running aggregate. Range keys are not fingerprinted but instead written to a pebble SST that is returned to the caller. This is because range keys do not have a stable, discrete identity and so it is up to the caller to define a deterministic fingerprinting scheme across all returned range keys. The fingerprintWriter is used by `MVCCExportFingerprint` that exports a fingerprint for point keys in the keyrange [StartKey, EndKey) over the interval (StartTS, EndTS]. The export logic used by `MVCCExportFingerprint` is the same that drives `MVCCExportToSST`. The former writes to a fingerprintWriter while the latter writes to an sstWriter. Currently, this method only support using an `fnv64` hasher to fingerprint each KV. This change does not wire `MVCCExportFingerprint` to ExportRequest command evaluation. This will be done as a followup. Informs: #89336 Release note: None
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,146 @@ | ||
| // 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 ( | ||
| "context" | ||
| "hash" | ||
| "io" | ||
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| "github.com/cockroachdb/cockroach/pkg/roachpb" | ||
| "github.com/cockroachdb/cockroach/pkg/settings/cluster" | ||
| "github.com/cockroachdb/errors" | ||
| ) | ||
|
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| // fingerprintWriter hashes every key/timestamp and value for point keys, and | ||
| // combines their hashes via a XOR into a running aggregate. | ||
| // | ||
| // Range keys are not fingerprinted but instead written to a pebble SST that is | ||
| // returned to the caller. This is because range keys do not have a stable, | ||
| // discrete identity and so it is up to the caller to define a deterministic | ||
| // fingerprinting scheme across all returned range keys. | ||
| // | ||
| // The caller must Finish() and Close() the fingerprintWriter to finalize the | ||
| // writes to the underlying pebble SST. | ||
| type fingerprintWriter struct { | ||
| hasher hash.Hash64 | ||
| timestampBuf []byte | ||
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| sstWriter *SSTWriter | ||
| xorAgg *uintXorAggregate | ||
| } | ||
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| // makeFingerprintWriter creates a new fingerprintWriter. | ||
| func makeFingerprintWriter( | ||
| ctx context.Context, hasher hash.Hash64, cs *cluster.Settings, f io.Writer, | ||
| ) fingerprintWriter { | ||
| // TODO(adityamaru,dt): Once | ||
| // https://github.com/cockroachdb/cockroach/issues/90450 has been addressed we | ||
| // should write to a kvBuf instead of a Backup SST writer. | ||
| sstWriter := MakeBackupSSTWriter(ctx, cs, f) | ||
| return fingerprintWriter{ | ||
| sstWriter: &sstWriter, | ||
| hasher: hasher, | ||
| xorAgg: &uintXorAggregate{}, | ||
| } | ||
| } | ||
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| type uintXorAggregate struct { | ||
| sum uint64 | ||
| } | ||
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| // add inserts one value into the running xor. | ||
| func (a *uintXorAggregate) add(x uint64) { | ||
| a.sum = a.sum ^ x | ||
| } | ||
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| // result returns the xor. | ||
| func (a *uintXorAggregate) result() uint64 { | ||
| return a.sum | ||
| } | ||
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| // Finish finalizes the underlying SSTWriter, and returns the aggregated | ||
| // fingerprint for point keys. | ||
| func (f *fingerprintWriter) Finish() (uint64, error) { | ||
| // If no records were added to the sstable, skip completing it. | ||
| if f.sstWriter.DataSize != 0 { | ||
| if err := f.sstWriter.Finish(); err != nil { | ||
| return 0, err | ||
| } | ||
| } | ||
| return f.xorAgg.result(), nil | ||
| } | ||
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| // Close finishes and frees memory and other resources. Close is idempotent. | ||
| func (f *fingerprintWriter) Close() { | ||
| if f.sstWriter == nil { | ||
| return | ||
| } | ||
| f.sstWriter.Close() | ||
| f.hasher.Reset() | ||
| f.xorAgg = nil | ||
| f.sstWriter = nil | ||
| } | ||
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| var _ ExportWriter = &fingerprintWriter{} | ||
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| // PutRawMVCCRangeKey implements the Writer interface. | ||
| func (f *fingerprintWriter) PutRawMVCCRangeKey(key MVCCRangeKey, bytes []byte) error { | ||
| // We do not fingerprint range keys, instead, we write them to a Pebble SST. | ||
| // This is because range keys do not have a stable, discrete identity and so | ||
| // it is up to the caller to define a deterministic fingerprinting scheme | ||
| // across all returned range keys. | ||
| return f.sstWriter.PutRawMVCCRangeKey(key, bytes) | ||
| } | ||
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| // PutRawMVCC implements the Writer interface. | ||
| func (f *fingerprintWriter) PutRawMVCC(key MVCCKey, value []byte) error { | ||
| defer f.hasher.Reset() | ||
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| // Hash the key/timestamp and value of the RawMVCC. | ||
| if err := f.hash(key.Key); err != nil { | ||
| return err | ||
| } | ||
| f.timestampBuf = EncodeMVCCTimestampToBuf(f.timestampBuf, key.Timestamp) | ||
| if err := f.hash(f.timestampBuf); err != nil { | ||
| return err | ||
| } | ||
| if err := f.hash(value); err != nil { | ||
| return err | ||
| } | ||
| f.xorAgg.add(f.hasher.Sum64()) | ||
| return nil | ||
| } | ||
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| // PutUnversioned implements the Writer interface. | ||
| func (f *fingerprintWriter) PutUnversioned(key roachpb.Key, value []byte) error { | ||
| defer f.hasher.Reset() | ||
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| // Hash the key and value in the absence of a timestamp. | ||
| if err := f.hash(key); err != nil { | ||
| return err | ||
| } | ||
| if err := f.hash(value); err != nil { | ||
| return err | ||
| } | ||
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| f.xorAgg.add(f.hasher.Sum64()) | ||
| return nil | ||
| } | ||
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| func (f *fingerprintWriter) hash(data []byte) error { | ||
| if _, err := f.hasher.Write(data); err != nil { | ||
| return errors.NewAssertionErrorWithWrappedErrf(err, | ||
| `"It never returns an error." -- https://golang.org/pkg/hash: %T`, f) | ||
| } | ||
|
|
||
| return nil | ||
| } |
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