Upstream changes

git-svn-id: https://leveldb.googlecode.com/svn/trunk@15 62dab493-f737-651d-591e-8d6aee1b9529

TODO

@@ -8,7 +8,6 @@ Maybe afterwards
 
 ss
 - Stats
-- Speed up backwards scan (avoid three passes over data)
 
 db
 - Maybe implement DB::BulkDeleteForRange(start_key, end_key)

db/db_bench.cc

@@ -11,6 +11,8 @@
 #include "include/db.h"
 #include "include/env.h"
 #include "include/write_batch.h"
+#include "port/port.h"
+#include "util/crc32c.h"
 #include "util/histogram.h"
 #include "util/random.h"
 #include "util/testutil.h"
@@ -25,6 +27,8 @@
 //      readseq       -- read N values sequentially
 //      readreverse   -- read N values in reverse order
 //      readrandom    -- read N values in random order
+//      crc32c        -- repeated crc32c of 4K of data
+//      sha1          -- repeated SHA1 computation over 4K of data
 //   Meta operations:
 //      compact     -- Compact the entire DB
 //      heapprofile -- Dump a heap profile (if supported by this port)
@@ -34,17 +38,21 @@
 //      normal      -- reset N back to its normal value (1000000)
 static const char* FLAGS_benchmarks =
     "fillseq,"
+    "fillsync,"
     "fillrandom,"
     "overwrite,"
-    "fillsync,"
+    "readrandom,"
+    "readrandom,"  // Extra run to allow previous compactions to quiesce
     "readseq,"
     "readreverse,"
-    "readrandom,"
     "compact,"
+    "readrandom,"
     "readseq,"
     "readreverse,"
-    "readrandom,"
-    "fill100K";
+    "fill100K,"
+    "crc32c,"
+    "sha1"
+    ;
 
 // Number of key/values to place in database
 static int FLAGS_num = 1000000;
@@ -330,6 +338,10 @@ class Benchmark {
         ReadRandom();
       } else if (name == Slice("compact")) {
         Compact();
+      } else if (name == Slice("crc32c")) {
+        Crc32c(4096, "(4K per op)");
+      } else if (name == Slice("sha1")) {
+        SHA1(4096, "(4K per op)");
       } else if (name == Slice("heapprofile")) {
         HeapProfile();
       } else {
@@ -340,6 +352,41 @@ class Benchmark {
   }
 
  private:
+  void Crc32c(int size, const char* label) {
+    // Checksum about 500MB of data total
+    string data(size, 'x');
+    int64_t bytes = 0;
+    uint32_t crc = 0;
+    while (bytes < 500 * 1048576) {
+      crc = crc32c::Value(data.data(), size);
+      FinishedSingleOp();
+      bytes += size;
+    }
+    // Print so result is not dead
+    fprintf(stderr, "... crc=0x%x\r", static_cast<unsigned int>(crc));
+
+    bytes_ = bytes;
+    message_ = label;
+  }
+
+  void SHA1(int size, const char* label) {
+    // SHA1 about 100MB of data total
+    string data(size, 'x');
+    int64_t bytes = 0;
+    char sha1[20];
+    while (bytes < 100 * 1048576) {
+      port::SHA1_Hash(data.data(), size, sha1);
+      FinishedSingleOp();
+      bytes += size;
+    }
+
+    // Print so result is not dead
+    fprintf(stderr, "... sha1=%02x...\r", static_cast<unsigned int>(sha1[0]));
+
+    bytes_ = bytes;
+    message_ = label;
+  }
+
   void Open() {
     assert(db_ == NULL);
     Options options;

db/db_iter.cc

@@ -36,6 +36,16 @@ namespace {
 // numbers, deletion markers, overwrites, etc.
 class DBIter: public Iterator {
  public:
+  // Which direction is the iterator currently moving?
+  // (1) When moving forward, the internal iterator is positioned at
+  //     the exact entry that yields this->key(), this->value()
+  // (2) When moving backwards, the internal iterator is positioned
+  //     just before all entries whose user key == this->key().
+  enum Direction {
+    kForward,
+    kReverse
+  };
+
   DBIter(const std::string* dbname, Env* env,
          const Comparator* cmp, Iterator* iter, SequenceNumber s)
       : dbname_(dbname),
@@ -44,6 +54,7 @@ class DBIter: public Iterator {
         iter_(iter),
         sequence_(s),
         large_(NULL),
+        direction_(kForward),
         valid_(false) {
   }
   virtual ~DBIter() {
@@ -53,48 +64,21 @@ class DBIter: public Iterator {
   virtual bool Valid() const { return valid_; }
   virtual Slice key() const {
     assert(valid_);
-    return key_;
+    return (direction_ == kForward) ? ExtractUserKey(iter_->key()) : saved_key_;
   }
   virtual Slice value() const {
     assert(valid_);
+    Slice raw_value = (direction_ == kForward) ? iter_->value() : saved_value_;
     if (large_ == NULL) {
-      return value_;
+      return raw_value;
     } else {
       MutexLock l(&large_->mutex);
       if (!large_->produced) {
-        ReadIndirectValue();
+        ReadIndirectValue(raw_value);
       }
       return large_->value;
     }
   }
-
-  virtual void Next() {
-    assert(valid_);
-    // iter_ is already positioned past DBIter::key()
-    FindNextUserEntry();
-  }
-
-  virtual void Prev() {
-    assert(valid_);
-    bool ignored;
-    ScanUntilBeforeCurrentKey(&ignored);
-    FindPrevUserEntry();
-  }
-
-  virtual void Seek(const Slice& target) {
-    ParsedInternalKey ikey(target, sequence_, kValueTypeForSeek);
-    std::string tmp;
-    AppendInternalKey(&tmp, ikey);
-    iter_->Seek(tmp);
-    FindNextUserEntry();
-  }
-  virtual void SeekToFirst() {
-    iter_->SeekToFirst();
-    FindNextUserEntry();
-  }
-
-  virtual void SeekToLast();
-
   virtual Status status() const {
     if (status_.ok()) {
       if (large_ != NULL && !large_->status.ok()) return large_->status;
@@ -104,23 +88,13 @@ class DBIter: public Iterator {
     }
   }
 
- private:
-  void FindNextUserEntry();
-  void FindPrevUserEntry();
-  void SaveKey(const Slice& k) { key_.assign(k.data(), k.size()); }
-  void SaveValue(const Slice& v) {
-    if (value_.capacity() > v.size() + 1048576) {
-      std::string empty;
-      swap(empty, value_);
-    }
-    value_.assign(v.data(), v.size());
-  }
-  bool ParseKey(ParsedInternalKey* key);
-  void SkipPast(const Slice& k);
-  void ScanUntilBeforeCurrentKey(bool* found_live);
-
-  void ReadIndirectValue() const;
+  virtual void Next();
+  virtual void Prev();
+  virtual void Seek(const Slice& target);
+  virtual void SeekToFirst();
+  virtual void SeekToLast();
 
+ private:
   struct Large {
     port::Mutex mutex;
     std::string value;
@@ -128,19 +102,42 @@ class DBIter: public Iterator {
     Status status;
   };
 
+  void FindNextUserEntry(bool skipping, std::string* skip);
+  void FindPrevUserEntry();
+  bool ParseKey(ParsedInternalKey* key);
+  void ReadIndirectValue(Slice ref) const;
+
+  inline void SaveKey(const Slice& k, std::string* dst) {
+    dst->assign(k.data(), k.size());
+  }
+
+  inline void ForgetLargeValue() {
+    if (large_ != NULL) {
+      delete large_;
+      large_ = NULL;
+    }
+  }
+
+  inline void ClearSavedValue() {
+    if (saved_value_.capacity() > 1048576) {
+      std::string empty;
+      swap(empty, saved_value_);
+    } else {
+      saved_value_.clear();
+    }
+  }
+
   const std::string* const dbname_;
   Env* const env_;
-
   const Comparator* const user_comparator_;
-
-  // iter_ is positioned just past current entry for DBIter if valid_
   Iterator* const iter_;
-
   SequenceNumber const sequence_;
+
   Status status_;
-  std::string key_;                  // Always a user key
-  std::string value_;
+  std::string saved_key_;     // == current key when direction_==kReverse
+  std::string saved_value_;   // == current raw value when direction_==kReverse
   Large* large_;              // Non-NULL if value is an indirect reference
+  Direction direction_;
   bool valid_;
 
   // No copying allowed
@@ -157,204 +154,189 @@ inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
   }
 }
 
-void DBIter::FindNextUserEntry() {
-  if (large_ != NULL) {
-    if (status_.ok() && !large_->status.ok()) {
-      status_ = large_->status;
+void DBIter::Next() {
+  assert(valid_);
+  ForgetLargeValue();
+
+  if (direction_ == kReverse) {  // Switch directions?
+    direction_ = kForward;
+    // iter_ is pointing just before the entries for this->key(),
+    // so advance into the range of entries for this->key() and then
+    // use the normal skipping code below.
+    if (!iter_->Valid()) {
+      iter_->SeekToFirst();
+    } else {
+      iter_->Next();
     }
-    delete large_;
-    large_ = NULL;
+    if (!iter_->Valid()) {
+      valid_ = false;
+      saved_key_.clear();
+      return;
     }
-  while (iter_->Valid()) {
-    ParsedInternalKey ikey;
-    if (!ParseKey(&ikey)) {
-      // Skip past corrupted entry
-      iter_->Next();
-      continue;
   }
-    if (ikey.sequence > sequence_) {
-      // Ignore entries newer than the snapshot
-      iter_->Next();
-      continue;
+
+  // Temporarily use saved_key_ as storage for key to skip.
+  std::string* skip = &saved_key_;
+  SaveKey(ExtractUserKey(iter_->key()), skip);
+  FindNextUserEntry(true, skip);
 }
 
+void DBIter::FindNextUserEntry(bool skipping, std::string* skip) {
+  // Loop until we hit an acceptable entry to yield
+  assert(iter_->Valid());
+  assert(direction_ == kForward);
+  assert(large_ == NULL);
+  do {
+    ParsedInternalKey ikey;
+    if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
       switch (ikey.type) {
         case kTypeDeletion:
-        SaveKey(ikey.user_key);  // Make local copy for use by SkipPast()
-        iter_->Next();
-        SkipPast(key_);
-        // Do not return deleted entries.  Instead keep looping.
+          // Arrange to skip all upcoming entries for this key since
+          // they are hidden by this deletion.
+          SaveKey(ikey.user_key, skip);
+          skipping = true;
           break;
-
         case kTypeValue:
-        SaveKey(ikey.user_key);
-        SaveValue(iter_->value());
-        iter_->Next();
-        SkipPast(key_);
-        // Yield the value we just found.
-        valid_ = true;
-        return;
-
         case kTypeLargeValueRef:
-        SaveKey(ikey.user_key);
-        // Save the large value ref as value_, and read it lazily on a call
-        // to value()
-        SaveValue(iter_->value());
+          if (skipping &&
+              user_comparator_->Compare(ikey.user_key, *skip) <= 0) {
+            // Entry hidden
+          } else {
+            valid_ = true;
+            saved_key_.clear();
+            if (ikey.type == kTypeLargeValueRef) {
               large_ = new Large;
               large_->produced = false;
-        iter_->Next();
-        SkipPast(key_);
-        // Yield the value we just found.
-        valid_ = true;
+            }
             return;
           }
+          break;
+      }
     }
+    iter_->Next();
+  } while (iter_->Valid());
+  saved_key_.clear();
   valid_ = false;
-  key_.clear();
-  value_.clear();
-  assert(large_ == NULL);
 }
 
-void DBIter::SkipPast(const Slice& k) {
-  while (iter_->Valid()) {
-    ParsedInternalKey ikey;
-    // Note that if we cannot parse an internal key, we keep looping
-    // so that if we have a run like the following:
-    //     <x,100,v> => value100
-    //     <corrupted entry for user key x>
-    //     <x,50,v> => value50
-    // we will skip over the corrupted entry as well as value50.
-    if (ParseKey(&ikey) && user_comparator_->Compare(ikey.user_key, k) != 0) {
+void DBIter::Prev() {
+  assert(valid_);
+  ForgetLargeValue();
+
+  if (direction_ == kForward) {  // Switch directions?
+    // iter_ is pointing at the current entry.  Scan backwards until
+    // the key changes so we can use the normal reverse scanning code.
+    assert(iter_->Valid());  // Otherwise valid_ would have been false
+    SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
+    while (true) {
+      iter_->Prev();
+      if (!iter_->Valid()) {
+        valid_ = false;
+        saved_key_.clear();
+        ClearSavedValue();
+        return;
+      }
+      if (user_comparator_->Compare(ExtractUserKey(iter_->key()),
+                                    saved_key_) < 0) {
         break;
       }
-    iter_->Next();
     }
+    direction_ = kReverse;
   }
 
-void DBIter::SeekToLast() {
-  // Position iter_ at the last uncorrupted user key and then
-  // let FindPrevUserEntry() do the heavy lifting to find
-  // a user key that is live.
-  iter_->SeekToLast();
-  ParsedInternalKey current;
-  while (iter_->Valid() && !ParseKey(&current)) {
-    iter_->Prev();
-  }
-  if (iter_->Valid()) {
-    SaveKey(current.user_key);
-  }
   FindPrevUserEntry();
 }
 
-// Let X be the user key at which iter_ is currently positioned.
-// Adjust DBIter to point at the last entry with a key <= X that
-// has a live value.
 void DBIter::FindPrevUserEntry() {
-  // Consider the following example:
-  //
-  //     A@540
-  //     A@400
-  //
-  //     B@300
-  //     B@200
-  //     B@100        <- iter_
-  //
-  //     C@301
-  //     C@201
-  //
-  // The comments marked "(first iteration)" below relate what happens
-  // for the preceding example in the first iteration of the while loop
-  // below.  There may be more than one iteration either if there are
-  // no live values for B, or if there is a corruption.
-  while (iter_->Valid()) {
-    std::string saved = key_;
-    bool found_live;
-    ScanUntilBeforeCurrentKey(&found_live);
-    // (first iteration) iter_ at A@400
-    if (found_live) {
-      // Step forward into range of entries with user key >= saved
-      if (!iter_->Valid()) {
-        iter_->SeekToFirst();
+  assert(direction_ == kReverse);
+  assert(large_ == NULL);
+
+  ValueType value_type = kTypeDeletion;
+  if (iter_->Valid()) {
+    SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
+    do {
+      ParsedInternalKey ikey;
+      if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
+        if ((value_type != kTypeDeletion) &&
+            user_comparator_->Compare(ikey.user_key, saved_key_) < 0) {
+          // We encountered a non-deleted value in entries for previous keys,
+          break;
+        }
+        value_type = ikey.type;
+        if (value_type == kTypeDeletion) {
+          ClearSavedValue();
         } else {
-        iter_->Next();
+          Slice raw_value = iter_->value();
+          if (saved_value_.capacity() > raw_value.size() + 1048576) {
+            std::string empty;
+            swap(empty, saved_value_);
           }
-      // (first iteration) iter_ at B@300
-
-      FindNextUserEntry();  // Sets key_ to the key of the next value it found
-      if (valid_ && user_comparator_->Compare(key_, saved) == 0) {
-        // (first iteration) iter_ at C@301
-        return;
+          saved_value_.assign(raw_value.data(), raw_value.size());
         }
-
-      // FindNextUserEntry() could not find any entries under the
-      // user key "saved".  This is probably a corruption since
-      // ScanUntilBefore(saved) found a live value.  So we skip
-      // backwards to an earlier key and ignore the corrupted
-      // entries for "saved".
-      //
-      // (first iteration) iter_ at C@301 and saved == "B"
-      key_ = saved;
-      bool ignored;
-      ScanUntilBeforeCurrentKey(&ignored);
-      // (first iteration) iter_ at A@400
       }
+      iter_->Prev();
+    } while (iter_->Valid());
   }
+
+  if (value_type == kTypeDeletion) {
+    // End
     valid_ = false;
-  key_.clear();
-  value_.clear();
+    saved_key_.clear();
+    ClearSavedValue();
+    direction_ = kForward;
+  } else {
+    valid_ = true;
+    if (value_type == kTypeLargeValueRef) {
+      large_ = new Large;
+      large_->produced = false;
     }
-
-void DBIter::ScanUntilBeforeCurrentKey(bool* found_live) {
-  *found_live = false;
-  if (!iter_->Valid()) {
-    iter_->SeekToLast();
   }
-
-  while (iter_->Valid()) {
-    ParsedInternalKey current;
-    if (!ParseKey(&current)) {
-      iter_->Prev();
-      continue;
 }
 
-    if (current.sequence > sequence_) {
-      // Ignore entries that are serialized after this read
-      iter_->Prev();
-      continue;
+void DBIter::Seek(const Slice& target) {
+  direction_ = kForward;
+  ForgetLargeValue();
+  ClearSavedValue();
+  saved_key_.clear();
+  AppendInternalKey(
+      &saved_key_, ParsedInternalKey(target, sequence_, kValueTypeForSeek));
+  iter_->Seek(saved_key_);
+  if (iter_->Valid()) {
+    FindNextUserEntry(false, &saved_key_ /* temporary storage */);
+  } else {
+    valid_ = false;
+  }
 }
 
-    const int cmp = user_comparator_->Compare(current.user_key, key_);
-    if (cmp < 0) {
-      SaveKey(current.user_key);
-      return;
-    } else if (cmp == 0) {
-      switch (current.type) {
-        case kTypeDeletion:
-          *found_live = false;
-          break;
-
-        case kTypeValue:
-        case kTypeLargeValueRef:
-          *found_live = true;
-          break;
+void DBIter::SeekToFirst() {
+  direction_ = kForward;
+  ForgetLargeValue();
+  ClearSavedValue();
+  iter_->SeekToFirst();
+  if (iter_->Valid()) {
+    FindNextUserEntry(false, &saved_key_ /* temporary storage */);
+  } else {
+    valid_ = false;
   }
-    } else {  // cmp > 0
-      *found_live = false;
 }
 
-    iter_->Prev();
-  }
+void DBIter::SeekToLast() {
+  direction_ = kReverse;
+  ForgetLargeValue();
+  ClearSavedValue();
+  iter_->SeekToLast();
+  FindPrevUserEntry();
 }
 
-void DBIter::ReadIndirectValue() const {
+void DBIter::ReadIndirectValue(Slice ref) const {
   assert(!large_->produced);
   large_->produced = true;
   LargeValueRef large_ref;
-  if (value_.size() != LargeValueRef::ByteSize()) {
+  if (ref.size() != LargeValueRef::ByteSize()) {
     large_->status = Status::Corruption("malformed large value reference");
     return;
   }
-  memcpy(large_ref.data, value_.data(), LargeValueRef::ByteSize());
+  memcpy(large_ref.data, ref.data(), LargeValueRef::ByteSize());
   std::string fname = LargeValueFileName(*dbname_, large_ref);
   RandomAccessFile* file;
   Status s = env_->NewRandomAccessFile(fname, &file);

db/db_test.cc

@@ -209,6 +209,16 @@ class DBTest {
       }
     }
   }
+
+  std::string IterStatus(Iterator* iter) {
+    std::string result;
+    if (iter->Valid()) {
+      result = iter->key().ToString() + "->" + iter->value().ToString();
+    } else {
+      result = "(invalid)";
+    }
+    return result;
+  }
 };
 
 TEST(DBTest, Empty) {
@@ -234,6 +244,180 @@ TEST(DBTest, PutDeleteGet) {
   ASSERT_EQ("NOT_FOUND", Get("foo"));
 }
 
+TEST(DBTest, IterEmpty) {
+  Iterator* iter = db_->NewIterator(ReadOptions());
+
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->Seek("foo");
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  delete iter;
+}
+
+TEST(DBTest, IterSingle) {
+  ASSERT_OK(Put("a", "va"));
+  Iterator* iter = db_->NewIterator(ReadOptions());
+
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->Seek("");
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->Seek("a");
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->Seek("b");
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  delete iter;
+}
+
+TEST(DBTest, IterMulti) {
+  ASSERT_OK(Put("a", "va"));
+  ASSERT_OK(Put("b", "vb"));
+  ASSERT_OK(Put("c", "vc"));
+  Iterator* iter = db_->NewIterator(ReadOptions());
+
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->Seek("");
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Seek("a");
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Seek("ax");
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Seek("b");
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Seek("z");
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  // Switch from reverse to forward
+  iter->SeekToLast();
+  iter->Prev();
+  iter->Prev();
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+
+  // Switch from forward to reverse
+  iter->SeekToFirst();
+  iter->Next();
+  iter->Next();
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+
+  // Make sure iter stays at snapshot
+  ASSERT_OK(Put("a",  "va2"));
+  ASSERT_OK(Put("a2", "va3"));
+  ASSERT_OK(Put("b",  "vb2"));
+  ASSERT_OK(Put("c",  "vc2"));
+  ASSERT_OK(Delete("b"));
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "b->vb");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  delete iter;
+}
+
+TEST(DBTest, IterSmallAndLargeMix) {
+  ASSERT_OK(Put("a", "va"));
+  ASSERT_OK(Put("b", std::string(100000, 'b')));
+  ASSERT_OK(Put("c", "vc"));
+  ASSERT_OK(Put("d", std::string(100000, 'd')));
+  ASSERT_OK(Put("e", std::string(100000, 'e')));
+
+  Iterator* iter = db_->NewIterator(ReadOptions());
+
+  iter->SeekToFirst();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "b->" + std::string(100000, 'b'));
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "d->" + std::string(100000, 'd'));
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "e->" + std::string(100000, 'e'));
+  iter->Next();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  iter->SeekToLast();
+  ASSERT_EQ(IterStatus(iter), "e->" + std::string(100000, 'e'));
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "d->" + std::string(100000, 'd'));
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "c->vc");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "b->" + std::string(100000, 'b'));
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "a->va");
+  iter->Prev();
+  ASSERT_EQ(IterStatus(iter), "(invalid)");
+
+  delete iter;
+}
+
 TEST(DBTest, Recover) {
   ASSERT_OK(Put("foo", "v1"));
   ASSERT_OK(Put("baz", "v5"));

doc/index.html

@@ -132,8 +132,7 @@ range <code>[start,limit)</code>:
   }
 </pre>
 You can also process entries in reverse order.  (Caveat: reverse
-iteration is currently a factor of two or three slower than forward
-iteration.)
+iteration may be somewhat slower than forward iteration.)
 <p>
 <pre>
   for (it-&gt;SeekToLast(); it-&gt;Valid(); it-&gt;Prev()) {

port/sha1_test.cc

@@ -31,22 +31,6 @@ TEST(SHA1, Simple) {
             TestSHA1(x.data(), x.size()));
 }
 
-TEST(SHA1, Benchmark) {
-  std::string data(1048576 * 100, 'x');
-  double start = Env::Default()->NowMicros() * 1e-6;
-  static const int kIters = 10;
-  uint32_t sha1 = 0;
-  for (int i = 0; i < kIters; i++) {
-    char hash_val[20];
-    SHA1_Hash(data.data(), data.size(), hash_val);
-    sha1 |= hash_val[0];
-  }
-  double finish = Env::Default()->NowMicros() * 1e-6;
-  double mb = (static_cast<long long int>(data.size()) * kIters) / 1048576.0;
-  fprintf(stderr, "SHA1 %0.0f MB: %.3f secs; %.1f MB/s, dummy=0x%02x\n",
-          mb, (finish - start), mb / (finish - start), sha1);
-}
-
 }
 }
 

util/crc32c_test.cc

@@ -64,20 +64,6 @@ TEST(CRC, Mask) {
   ASSERT_EQ(crc, Unmask(Unmask(Mask(Mask(crc)))));
 }
 
-TEST(CRC, Benchmark) {
-  std::string data(1048576 * 100, 'x');
-  double start = Env::Default()->NowMicros() * 1e-6;
-  static const int kIters = 10;
-  uint32_t crc = 0;
-  for (int i = 0; i < kIters; i++) {
-    crc |= Value(data.data(), data.size());
-  }
-  double finish = Env::Default()->NowMicros() * 1e-6;
-  double mb = (static_cast<long long int>(data.size()) * kIters) / 1048576.0;
-  fprintf(stderr, "CRC %0.0f MB: %.3f secs; %.1f MB/s, crc=0x%08x\n",
-          mb, (finish - start), mb / (finish - start), crc);
-}
-
 }
 }