LCOV - code coverage report
Current view: top level - pebble/sstable/block - kv.go (source / functions) Hit Total Coverage
Test: 2024-10-11 08:16Z fb2c2ff4 - meta test only.lcov Lines: 21 21 100.0 %
Date: 2024-10-11 08:17:29 Functions: 0 0 -

          Line data    Source code
       1             : // Copyright 2024 The LevelDB-Go and Pebble Authors. All rights reserved. Use
       2             : // of this source code is governed by a BSD-style license that can be found in
       3             : // the LICENSE file.
       4             : 
       5             : package block
       6             : 
       7             : import "github.com/cockroachdb/pebble/internal/base"
       8             : 
       9             : // ValuePrefix is the single byte prefix in values indicating either an in-place
      10             : // value or a value encoding a valueHandle. It encodes multiple kinds of
      11             : // information (see below).
      12             : type ValuePrefix byte
      13             : 
      14             : const (
      15             :         // 2 most-significant bits of valuePrefix encodes the value-kind.
      16             :         valueKindMask           ValuePrefix = 0xC0
      17             :         valueKindIsValueHandle  ValuePrefix = 0x80
      18             :         valueKindIsInPlaceValue ValuePrefix = 0x00
      19             : 
      20             :         // 1 bit indicates SET has same key prefix as immediately preceding key that
      21             :         // is also a SET. If the immediately preceding key in the same block is a
      22             :         // SET, AND this bit is 0, the prefix must have changed.
      23             :         //
      24             :         // Note that the current policy of only storing older MVCC versions in value
      25             :         // blocks means that valueKindIsValueHandle => SET has same prefix. But no
      26             :         // code should rely on this behavior. Also, SET has same prefix does *not*
      27             :         // imply valueKindIsValueHandle.
      28             :         setHasSameKeyPrefixMask ValuePrefix = 0x20
      29             : 
      30             :         // 3 least-significant bits for the user-defined base.ShortAttribute.
      31             :         // Undefined for valueKindIsInPlaceValue.
      32             :         userDefinedShortAttributeMask ValuePrefix = 0x07
      33             : )
      34             : 
      35             : // IsValueHandle returns true if the ValuePrefix is for a valueHandle.
      36           1 : func (vp ValuePrefix) IsValueHandle() bool {
      37           1 :         return vp&valueKindMask == valueKindIsValueHandle
      38           1 : }
      39             : 
      40             : // SetHasSamePrefix returns true if the ValuePrefix encodes that the key is a
      41             : // set with the same prefix as the preceding key which also is a set.
      42           1 : func (vp ValuePrefix) SetHasSamePrefix() bool {
      43           1 :         return vp&setHasSameKeyPrefixMask == setHasSameKeyPrefixMask
      44           1 : }
      45             : 
      46             : // ShortAttribute returns the user-defined base.ShortAttribute encoded in the
      47             : // ValuePrefix.
      48             : //
      49             : // REQUIRES: IsValueHandle()
      50           1 : func (vp ValuePrefix) ShortAttribute() base.ShortAttribute {
      51           1 :         return base.ShortAttribute(vp & userDefinedShortAttributeMask)
      52           1 : }
      53             : 
      54             : // ValueHandlePrefix returns the ValuePrefix for a valueHandle.
      55           1 : func ValueHandlePrefix(setHasSameKeyPrefix bool, attribute base.ShortAttribute) ValuePrefix {
      56           1 :         prefix := valueKindIsValueHandle | ValuePrefix(attribute)
      57           1 :         if setHasSameKeyPrefix {
      58           1 :                 prefix = prefix | setHasSameKeyPrefixMask
      59           1 :         }
      60           1 :         return prefix
      61             : }
      62             : 
      63             : // InPlaceValuePrefix returns the ValuePrefix for an in-place value.
      64           1 : func InPlaceValuePrefix(setHasSameKeyPrefix bool) ValuePrefix {
      65           1 :         prefix := valueKindIsInPlaceValue
      66           1 :         if setHasSameKeyPrefix {
      67           1 :                 prefix = prefix | setHasSameKeyPrefixMask
      68           1 :         }
      69           1 :         return prefix
      70             : }
      71             : 
      72             : // GetLazyValueForPrefixAndValueHandler is an interface for getting a LazyValue
      73             : // from a value prefix and value.
      74             : type GetLazyValueForPrefixAndValueHandler interface {
      75             :         GetLazyValueForPrefixAndValueHandle(handle []byte) base.LazyValue
      76             : }

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