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Improve documentation of SliceTransform.

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Test Plan: make check

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D61875
This commit is contained in:
Dhruba Borthakur 2016-08-10 16:21:37 -07:00
parent 6056d6317d
commit d1be594636
1 changed files with 28 additions and 5 deletions
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33
include/rocksdb/slice_transform.h
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@ -21,6 +21,12 @@ namespace rocksdb {
class Slice;
/*
* A SliceTranform is a generic pluggable way of transforming one string
* to another. Its primary use-case is in configuring rocksdb
* to store prefix blooms by setting prefix_extractor in
* ColumnFamilyOptions.
*/
class SliceTransform {
public:
virtual ~SliceTransform() {};
@ -28,13 +34,30 @@ class SliceTransform {
// Return the name of this transformation.
virtual const char* Name() const = 0;
// transform a src in domain to a dst in the range
virtual Slice Transform(const Slice& src) const = 0;
// Extract a prefix from a specified key. This method is called when
// a key is inserted into the db, and the returned slice is used to
// create a bloom filter.
virtual Slice Transform(const Slice& key) const = 0;
// determine whether this is a valid src upon the function applies
virtual bool InDomain(const Slice& src) const = 0;
// Determine whether the specified key is compatible with the logic
// specified in the Transform method. This method is invoked for every
// key that is inserted into the db. If this method returns true,
// then Transform is called to translate the key to its prefix and
// that returned prefix is inserted into the bloom filter. If this
// method returns false, then the call to Transform is skipped and
// no prefix is inserted into the bloom filters.
//
// For example, if the Transform method operates on a fixed length
// prefix of size 4, then an invocation to InDomain("abc") returns
// false because the specified key length(3) is shorter than the
// prefix size of 4.
//
// Wiki documentation here:
// https://github.com/facebook/rocksdb/wiki/Prefix-Seek-API-Changes
//
virtual bool InDomain(const Slice& key) const = 0;
// determine whether dst=Transform(src) for some src
// This is currently not used and remains here for backward compatibility.
virtual bool InRange(const Slice& dst) const = 0;
// Transform(s)=Transform(`prefix`) for any s with `prefix` as a prefix.