Added bloom filter support.v1.4

In particular, we add a new FilterPolicy class.  An instance
of this class can be supplied in Options when opening a
database.  If supplied, the instance is used to generate
summaries of keys (e.g., a bloom filter) which are placed in
sstables.  These summaries are consulted by DB::Get() so we
can avoid reading sstable blocks that are guaranteed to not
contain the key we are looking for.

This change provides one implementation of FilterPolicy
based on bloom filters.

Other changes:
- Updated version number to 1.4.
- Some build tweaks.
- C binding for CompactRange.
- A few more benchmarks: deleteseq, deleterandom, readmissing, seekrandom.
- Minor .gitignore update.

1 files changed, 8 insertions, 0 deletions

diff --git a/include/leveldb/options.h b/include/leveldb/options.h
index 79111a0..fdda718 100644
--- a/include/leveldb/options.h
+++ b/include/leveldb/options.h
@@ -12,6 +12,7 @@ namespace leveldb {
 class Cache;
 class Comparator;
 class Env;
+class FilterPolicy;
 class Logger;
 class Snapshot;
 
@@ -127,6 +128,13 @@ struct Options {
   // efficiently detect that and will switch to uncompressed mode.
   CompressionType compression;
 
+  // If non-NULL, use the specified filter policy to reduce disk reads.
+  // Many applications will benefit from passing the result of
+  // NewBloomFilterPolicy() here.
+  //
+  // Default: NULL
+  const FilterPolicy* filter_policy;
+
   // Create an Options object with default values for all fields.
   Options();
 };