Line data    Source code

       1             : // Copyright 2011 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 base
       6             : 
       7             : // SSTable block defaults.
       8             : const (
       9             :         DefaultBlockRestartInterval = 16
      10             :         DefaultBlockSize            = 4096
      11             :         DefaultBlockSizeThreshold   = 90
      12             : )
      13             : 
      14             : // FilterType is the level at which to apply a filter: block or table.
      15             : type FilterType int
      16             : 
      17             : // The available filter types.
      18             : const (
      19             :         TableFilter FilterType = iota
      20             : )
      21             : 
      22           2 : func (t FilterType) String() string {
      23           2 :         switch t {
      24           2 :         case TableFilter:
      25           2 :                 return "table"
      26             :         }
      27           0 :         return "unknown"
      28             : }
      29             : 
      30             : // FilterWriter provides an interface for creating filter blocks. See
      31             : // FilterPolicy for more details about filters.
      32             : type FilterWriter interface {
      33             :         // AddKey adds a key to the current filter block.
      34             :         AddKey(key []byte)
      35             : 
      36             :         // Finish appends to dst an encoded filter tha holds the current set of
      37             :         // keys. The writer state is reset after the call to Finish allowing the
      38             :         // writer to be reused for the creation of additional filters.
      39             :         Finish(dst []byte) []byte
      40             : }
      41             : 
      42             : // FilterPolicy is an algorithm for probabilistically encoding a set of keys.
      43             : // The canonical implementation is a Bloom filter.
      44             : //
      45             : // Every FilterPolicy has a name. This names the algorithm itself, not any one
      46             : // particular instance. Aspects specific to a particular instance, such as the
      47             : // set of keys or any other parameters, will be encoded in the []byte filter
      48             : // returned by NewWriter.
      49             : //
      50             : // The name may be written to files on disk, along with the filter data. To use
      51             : // these filters, the FilterPolicy name at the time of writing must equal the
      52             : // name at the time of reading. If they do not match, the filters will be
      53             : // ignored, which will not affect correctness but may affect performance.
      54             : type FilterPolicy interface {
      55             :         // Name names the filter policy.
      56             :         Name() string
      57             : 
      58             :         // MayContain returns whether the encoded filter may contain given key.
      59             :         // False positives are possible, where it returns true for keys not in the
      60             :         // original set.
      61             :         MayContain(ftype FilterType, filter, key []byte) bool
      62             : 
      63             :         // NewWriter creates a new FilterWriter.
      64             :         NewWriter(ftype FilterType) FilterWriter
      65             : }
      66             : 
      67             : // BlockPropertyFilter is used in an Iterator to filter sstables and blocks
      68             : // within the sstable. It should not maintain any per-sstable state, and must
      69             : // be thread-safe.
      70             : type BlockPropertyFilter interface {
      71             :         // Name returns the name of the block property collector.
      72             :         Name() string
      73             :         // Intersects returns true if the set represented by prop intersects with
      74             :         // the set in the filter.
      75             :         Intersects(prop []byte) (bool, error)
      76             : }